Early Mars hydrology:
Hydrological evolution in the Noachian and Hesperian epochs
Jeffrey C. Andrews-Hanna1
Kevin W. Lewis2
1
Department of Geophysics and Center for Space Resources
Colorado School of Mines
1500 Illinois St.
Golden, CO 80401
2
Department of Geosciences
Princeton University
Princeton NJ 08544
*e-mail jcahanna@mines.edu
62 pages
10 Figures
Submitted to the Journal of Geophysical Research-Planets on August 5th, 2010
Submitted in revised form on November 13th, 2010
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Abstract.
Mars was warmer and wetter during the early to middle Noachian, before a hydrologic and
climatic transition in the late Noachian led to a decrease in erosion rates, a change in valley
network morphology, and a geochemical shift from phyllosilicate to sulfate formation that
culminated in the formation of widespread sulfate-rich sedimentary deposits in Meridiani
Planum and the surrounding Arabia Terra region. This secular evolution was overprinted by
episodic and periodic variability, as recorded in the fluvial record, sedimentary layering, and
erosional discontinuities. We investigate the temporal evolution of martian groundwater
hydrology during the Noachian and early Hesperian epochs using global-scale hydrological
models. The results suggest that the more active hydrological cycle in the Noachian was a result
of a greater total water inventory, causing a saturated near-surface and high precipitation rates.
The late Noachian hydrologic, climatic, and geochemical transition can be explained by a
fundamental shift in the hydrological regime driven by a net loss of water due to impact and
solar wind erosion of the atmosphere. Following this transition, the water table retreated deep
beneath the surface, except in isolated regions of focused groundwater upwelling and
evaporation, producing the playa evaporites in Meridiani Planum and Arabia Terra. This longterm evolution was modulated by shorter-term climate forcing in the form of periodic and
chaotic variations in the orbital parameters of Mars, resulting in changes in the volume of water
sequestered in the polar caps and cryosphere. This shorter-term forcing can explain the observed
periodic and bundled sedimentary layering, erosional unconformities, and evidence for a
fluctuating water table at Meridiani Planum.
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1. Introduction
The ancient surfaces of Mars preserve a record of warmer and wetter conditions in which
liquid water played an important role in shaping the surface. Multiple lines of evidence are
converging towards a consensus picture of the phenomenological history of water on early Mars.
In the early Noachian, conditions were generally warmer and wetter than today, though likely
arid by terrestrial standards [Howard et al., 2005; Stepinski and Stepinski, 2005; Barnhart et al.,
2009]. These conditions led to the formation of dendritic valley networks [Carr and Malin,
2000; Craddock and Howard, 2002; Hynek and Phillips, 2003] and resulted in the alteration of
some of the near-surface materials to phyllosilicates [Poulet et al., 2005; Bibring et al., 2006]. A
significant shift in the ambient environment in the late Noachian led to drier conditions, as
recorded in a transition from dense runoff valleys to more sparsely dissected networks [Baker
and Partridge, 1986; Harrison and Grimm, 2005], the cessation of valley network formation
[Fassett and Head, 2008], a decrease in erosion rates [Golombek et al., 2006], and a change from
widespread phyllosilicate alteration [Poulet et al., 2005] to the formation of localized evaporitic
sulfate deposits [Bibring et al., 2006; Squyres et al., 2006].
The late Noachian to early
Hesperian epochs were characterized by the formation of widespread playa evaporites in
Meridiani Planum and related sedimentary deposits throughout the surrounding Arabia Terra
region [Andrews-Hanna et al., 2010]. This secular evolution was overprinted by temporal
variability on shorter timescales, expressed in the geologic record in evidence for a pulse of
enhanced valley network formation in the Late Noachian [Irwin et al., 2005], periodic layering
and bundling of layers within sedimentary deposits [Lewis et al., 2008], and erosional
unconformities within the Meridiani sulfate deposits [Wiseman et al., 2010].
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This evidence for hydrologic and climatic variability over multiple timescales motivates a
more detailed treatment of the time evolution of the hydrology of early Mars. We here use
models of the global scale groundwater hydrology to investigate the distribution and behavior of
water on Mars during the Noachian and early Hesperian epochs, and the temporal variability of
the hydrological cycle. In a companion paper, we focused on the hydrology in the late Noachian
to early Hesperian, at the time that the Meridiani Planum playa deposits and other sulfate
deposits were forming in response to sustained groundwater upwelling [Andrews-Hanna et al.,
2010]. That study investigated the hydrology under stable surface environmental conditions
without any external forcing.
In this study, we focus on the temporal variability of the
hydrologic cycle through the Noachian and Hesperian epochs. The current work incorporates the
effects of secular changes in the hydrologically available water inventory driven by solar wind
stripping and impact erosion as well as short-term variability induced by ice sequestration in the
polar caps and high latitude permafrost in response to periodic and chaotic changes in obliquity.
This study considers only the effects of the changing water inventory on the hydrology, and does
not consider the effects of likely contemporaneous changes in temperature.
The model results are shown to be consistent with the evidence for both the long- and
short-term hydrologic and climatic evolution of Mars. Early in Mars history, a large total water
inventory fueled high precipitation rates and a saturated near-surface zone, consistent with the
widespread formation of phyllosilicates and valley networks in the early to middle Noachian. A
net loss of water then drove a hydrologic and climatic transition in the late Noachian from wet
conditions with a high level of surface and near-surface hydrologic activity, to arid conditions
with a more sluggish hydrologic cycle and a surface that is desiccated across much of the planet.
Following this transition, predicted regions of groundwater upwelling and evaporation match the
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observed distribution of sulfate-rich sedimentary deposits.
Overprinting this long-term
evolution, short-term changes in the available water inventory in response to periodic and chaotic
changes in obliquity resulted in significant short-term variations in the precipitation and
groundwater upwelling rates and the depth to the water table. These variations are shown to be
consistent with the evidence for layer periodicity and bundling, and erosional discontinuities in
the sedimentary record.
2. Observational constraints on the temporal evolution of martian hydrology
2.1. Secular evolution and the late Noachian transition
The widespread dendritic valley networks found throughout the low latitude Noachianaged terrains provide compelling evidence for more Earth-like conditions on early Mars [Carr
and Clow, 1981; Baker, 1982; Carr and Chuang, 1997]. On the basis of the low drainage
densities [Carr and Chuang, 1997] and morphologies similar to terrestrial groundwater sapping
valleys on the Earth, it has been suggested that liquid precipitation and surface runoff may not
have been required [Goldspiel and Squyres, 2000]. However, groundwater sapping mechanisms
still require aquifer recharge, which must be brought about through either liquid precipitation or
the accumulation and melt of snow, both of which would require warmer and wetter conditions
than the current hyper-arid cold desert. More recent high-resolution imaging and topographic
data (Figure 1a) revealed that the drainage densities across much of Mars were significantly
higher than previously thought [Irwin and Howard, 2002; Hynek and Phillips, 2003; Hynek et
al., 2010], strengthening the argument for liquid precipitation.
Quantitative geomorphic analyses of the valley networks and comparisons to terrestrial
fluvial systems suggest that conditions on early Mars were comparable to those on the Earth in
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arid environments today [Stepinski and Stepinski, 2005; Barnhart et al., 2009], consistent with
the low erosion rates calculated for early Mars [Golombek et al., 2006]. A progression of valley
network morphology is generally observed, from early formation of densely dissected, V-shaped,
degraded valley networks suggestive of precipitation-induced runoff, to later formation of more
sparsely dissected, U-shaped, pristine valley networks [Baker and Partridge, 1986; Williams and
Phillips, 2001; Harrison and Grimm, 2005]. This transition has been interpreted as a result of
either an increased contribution from groundwater sapping [Baker and Partridge, 1986; Williams
and Phillips, 2001; Harrison and Grimm, 2005] or occasional flash-flooding under arid
conditions [Lamb et al., 2008].
Either interpretation of the transition in valley network
morphologies suggests a drying of the climate with time, with a decrease in the precipitation and
erosion rates and an increase in the depth to the water table below the surface [Harrison and
Grimm, 2005].
This transition in the fluvial geomorphology was approximately
contemporaneous with a decrease in the average surface erosion rates by several orders of
magnitude in the late Noachian to early Hesperian [Golombek et al., 2006]. Similarly, landscape
evolution models argue for a transition from both diffusive and advective erosion by rain splash
and runoff, to primarily diffusive erosion by rain splash and mass wasting, arguing for increased
infiltration and decreased runoff on an increasingly arid Mars [Craddock and Howard, 2002].
The record of both fluvial and non-fluvial erosion thus suggests that conditions in the Early
Noachian were at least transiently similar to arid or semi-arid environments on the Earth, but the
surface became increasingly desiccated with time.
These geomorphic interpretations of a climatic and hydrologic transition are corroborated
by spectral observations of the Martian surface indicating a concomitant mineralogical transition.
Spectral signatures indicative of the presence of phyllosilicates, including smectite,
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montmorillonite, and kaolinite, have been detected within ancient Noachian terrains across much
of Mars (Figure 1b) [Poulet et al., 2005; Bibring et al., 2006; Mustard et al., 2008b].
Stratigraphic relationships suggest that phyllosilicate alteration preceded the formation of the
fluvial channels in at least some portions of the planet [Mustard et al., 2008a]. This is supported
by improved estimates of valley network ages that place the termination of valley network
formation at the Noachian-Hesperian boundary [Fassett and Head, 2008], after the termination
of phyllosilicate formation prior to the end of the late Noachian [Bibring et al., 2006]. The early
era of phyllosilicate formation was followed by an era of sulfate deposition in the late Noachian
to early Hesperian [Bibring et al., 2006].
Unlike the widespread phyllosilicate deposits
interspersed within the crust, the sulfates are generally stratigraphically above the ancient
Noachian surfaces [e.g., Wiseman et al., 2008], and are localized primarily within the Meridiani
Planum region in western Arabia Terra, as well as within the Valles Marineris canyons and chaos
regions at the heads of the outflow channels [Gendrin et al., 2005; Murchie et al., 2009; Roach et
al., 2010b]. The hydrated sulfate deposits are commonly associated with layered outcrops
interpreted as sedimentary rocks (Figure 1c) [Malin and Edgett, 2000].
In situ observations by the Mars Exploration Rover Opportunity at Meridiani Planum led
to the interpretation of these deposits as evaporitic sulfate salts that have been extensively
reworked by fluvial and aeolian processes in a playa-like environment, followed by multiple
episodes of groundwater-mediated diagenesis [Grotzinger et al., 2005; McLennan et al., 2005;
Squyres and Knoll, 2005; Arvidson et al., 2006; Squyres et al., 2006]. A similar origin has been
suggested for the deposits in the canyons and chaos regions to the west, based on the
stratigraphic similarities and the co-occurrence of sulfates and hematite observed in both locales
[Glotch and Rogers, 2007; Murchie et al., 2009; Roach et al., 2010a], as well as similarities in
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the hydrological environment [Murchie et al., 2009]. Sulfate deposits outside of Arabia Terra,
Valles Marineris, and the chaos regions appear to be restricted to isolated crater lakes such as
Columbus crater to the west of Tharsis [Wray et al., 2009].
The transition from global
phyllosilicate alteration to local and regional sulfate deposition has been suggested to signal a
distinct change in the surface geochemical environment to more acidic and sulfate-rich
conditions [Bibring et al., 2006], the cause of which is investigated in this work.
The phyllosilicate-sulfate mineralogical and geochemical transition approximately
coincides with the transitions in erosion rates and valley network morphology, suggesting a
significant global hydrological, geochemical, and climatic change in the Late Noachian. This
transition resulted in an increasingly arid surface, an increase in the depth to the water table, a
decrease in the precipitation rates, and a transition from phyllosilicate to sulfate deposition.
Arid, yet not fully desiccated, conditions then persisted in the Late Noachian and Early
Hesperian, allowing the growth of local evaporite deposits while other evidence for water on the
surface waned. Eventually, Mars transitioned into a colder climate, and further hydrological
activity was limited to occasional outburst floods escaping from pressurized aquifers beneath a
thick cryosphere to carve the outflow channels [Hanna and Phillips, 2006; Andrews-Hanna and
Phillips, 2007].
2.2. Short-term periodic and episodic evolution
The long-term secular drying of the surface and near-surface environment during the
Noachian and Early Hesperian was overprinted by shorter-term temporal variability. Layering at
the mm- to cm-scale observed by the Mars Exploration Rover Opportunity [Grotzinger et al.,
2005] records the shortest timescale of variability. This finest scale layering may correspond to
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annual cycles, individual sand avalanches down the slip faces of dunes, or other short timescale
phenomena, but likely tells us little about the long-term climate evolution. A regular periodicity
in the thickness of meter-scale layers deduced from HiRISE images and stereotopography for
deposits across much of Mars argues for a periodic forcing mechanism (Figure 2a), likely
supplied by orbital-driven periodicity in the climate evolution [Lewis et al., 2010] (also K. W.
Lewis, Geologic setting of rhythmic sedimentary rocks on Mars, manuscript in preparation,
2010). Orbital control of the sedimentation is most clearly manifest in the cyclical bundling of
layers into packets of 10 at Becquerel crater (Figure 2b), which correlates with the 1.2 Myr cycle
that modulates the maximum obliquity achieved during the shorter 120 kyr obliquity cycles
[Laskar et al., 2004; Lewis et al., 2008].
Variability of a more episodic, rather than periodic, nature is also observed in the
geomorphic and sedimentary record.
Erosional unconformities are observed in outcrops
observed by Opportunity (such as the Wellington contact; Figure 2c) [Grotzinger et al., 2005] as
well as in sedimentary layering in HiRISE images (Figure 2d, e), suggesting temporary hiatuses
in deposition accompanied by erosion of the deposits that could result from a change in the
hydrologic or climatic environment. While angular unconformities such as these are observed
relatively rarely from remotely sensed data, other depositional hiatuses may not have led to
actual erosion of underlying strata before deposition resumed.
The resulting parallel
stratification would make detection of such an unconformity nearly impossible from orbit.
Smaller scale truncation surfaces in homogeneous lithologies such as the example from
Meridiani Planum may be common, but would be indiscernible to orbital instruments. On a
larger scale, geomorphic and mineralogical mapping of the Meridiani deposits revealed a lateral
facies change caused by erosion into preexisting layered deposits followed by deposition of
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relatively late stage sulfates, also suggestive of a hiatus in deposition leading to net erosion of the
deposits, followed by continued sulfate deposition [Wiseman et al., 2010]. A similar erosional
unconformity has been documented within the interior layered deposits in western Candor
Chasma [Fueten et al., 2008].
Evidence also suggests temporal variability in the rate of valley network formation.
Globally, valley network formation appears to have peaked towards the end of the Noachian
[Howard et al., 2005; Irwin et al., 2005; Fassett and Head, 2008], reflecting a late increase in
fluvial activity. Smaller-scale spatio-temporal variability in valley network activity is observed
on the scale of individual drainage basins [Hoke and Hynek, 2009]. Combined with the evidence
for a drying of the climate and a mineralogical transition in the late Noachian to early Hesperian,
this late stage pulse of fluvial activity suggests that the transition from wet to dry conditions may
have been both rapid and complex, possibly involving some overlap or inter-fingering of the
periods of fluvial erosion and sulfate deposition.
Taken together, these various lines of evidence point towards short- and long-term
variability in the hydrologic and climatic cycle of early Mars. This variability includes both
periodic variations on timescales of 120 kyr to 1.2 Myr expressed in sedimentary layering, as
well as episodic shifts in the hydrologic-climatic conditions expressed in erosional
unconformities and changes in the rate and style of fluvial modification of the surface. While the
concept of a transition from warm and wet to cold and dry conditions still holds to first order,
this secular evolution was overprinted by the more complex behavior expected of a real climate
system. While previous models of the hydrologic evolution of Mars have been successful in
reproducing the observed equatorial sulfate deposits in Meridiani Planum and Arabia Terra
[Andrews-Hanna et al., 2007; Andrews-Hanna et al., 2010], it is necessary to consider a more
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realistic representation of the temporal evolution of the hydrologic-climatic system. In the
following sections, we investigate the temporal evolution of the hydrological cycle on early Mars
from a groundwater perspective, focusing on the distributions of valley networks and
sedimentary deposits, the underlying mechanisms controlling the Late Noachian hydrologic,
climatic and geochemical transition, and the short-term variability in the hydrological cycle.
3. Groundwater model description
We model the groundwater hydrology of early Mars using a fully-explicit finite
difference code representing unconfined groundwater flow in a spherical shell grid [AndrewsHanna et al., 2007; Andrews-Hanna et al., 2010]. The models were run at a spatial resolution of
2.5 degrees per pixel. The aquifer properties are taken from the megaregolith model of Hanna
and Phillips [2005]. Groundwater flow is driven by gradients in the hydraulic head, which are
established as a result of precipitation-induced recharge in the low-latitudes and evaporative loss
of groundwater in regions where the water table reaches the surface. Full details and benchmarking of the hydrological model can be found in the companion paper [Andrews-Hanna et al.,
2010].
Conditions on early Mars are assumed to be arid by terrestrial standards, even during the
period of valley network formation, as suggested by the low drainage densities and immature
state of the fluvial landscape [Howard et al., 2005; Stepinski and Stepinski, 2005; Barnhart et al.,
2009]. Groundwater is assumed to evaporate upon reaching the surface, thereby limiting the
water table to remain at or beneath the surface. The presence of small-scale lakes and seas
would not greatly affect the large-scale patterns of groundwater flow, since they would exist
below the model resolution and would only change the local hydraulic head by a small amount.
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Large oceans in the northern lowlands [e.g., Di Achille and Hynek, 2010] or the Hellas and
Argyre impact basins [Moore and Wilhelms, 2001] would have a more significant effect on the
patterns of groundwater flow, though the existence of such water bodies is controversial. The
model does not include such possible ancient oceans or seas, though their possible effect is
discussed in section 4.
The globally integrated evaporative loss of water in each time step is redistributed over
the surface in a low-latitude precipitation belt, following a half-cosine distribution between ±45°
latitude to match the first-order distribution of valley networks. This implicitly assumes that the
conditions that prevented high latitude valley network formation would have inhibited aquifer
recharge as well. The lack of high latitude valley networks may be a result of either a lack of
precipitation, or persistently cold temperatures that would have prevented both runoff and
infiltration of precipitation.
The companion paper [Andrews-Hanna et al., 2010] demonstrated the importance of the
dynamic interaction between the hydrology and the surface topography. Groundwater-mediated
sedimentation alters the surface topography, which in turn alters the distribution and flow paths
of groundwater. The formation of evaporites and evaporite cemented sedimentary deposits is
represented in the models by assuming a groundwater salinity upon reaching the surface equal to
80% that of seawater [e.g., Handford, 1991], and that the deposits incorporate 50% by volume of
clastic sediments based on mini-TES observations at Meridiani [Glotch et al., 2006] and similar
to other dirty evaporites in playa settings, such that evaporation of 100 m of groundwater
produces 2 m of sediments.
Assuming either different fluid salinities or different aquifer
permeabilities results in a simple scaling of the rate of fluid flow and deposition. While there are
great uncertainties in both of these parameters, the previous study found that the predicted rates
12
of sedimentary deposition in Becquerel crater closely match the rates inferred from a correlation
of the layer periodicity with the timescale of obliquity variations [Lewis et al., 2008; AndrewsHanna et al., 2010].
4. Long-term hydrological evolution during the Noachian and Hesperian
4.1. Hydrological controls on sulfate deposition
We first briefly review the results of the earlier work on the groundwater-mediated
formation of evaporitic sulfates in the Late Noachian to Early Hesperian [Andrews-Hanna et al.,
2007; Andrews-Hanna et al., 2010]. Previous groundwater hydrology models found that
Meridiani Planum and the surrounding Arabia Terra region were areas of focused groundwater
upwelling to the surface, driven by the regional topography of Arabia Terra [Andrews-Hanna et
al., 2007]. In short, the breaks in slope on the northern and southern edges of Arabia Terra
separating it from the lowlands and highlands, together with its location in the low-latitudes
where precipitation-induced recharge of aquifers was likely, led to a net flux of groundwater to
the surface resulting in the formation of evaporites and evaporite cemented sediments.
Subsequent high-resolution global and regional groundwater models that explicitly
included the growth of sedimentary deposits through evaporite deposition and cementation of
aeolian debris strengthened this prediction [Andrews-Hanna et al., 2010].
These models
successfully predicted the approximate thickness and spatial extent of the Meridiani deposits, but
also predicted that they should be part of a more extensive set of deposits covering much of the
Arabia Terra region. These predictions were borne out by observations of layered deposits, large
intra-crater deposits, and pedestal craters that preserve the remnant of this once more extensive
set of deposits [Fassett and Head, 2007; Fergason and Christensen, 2008; Andrews-Hanna et
13
al., 2010; Zabrusky and Andrews-Hanna, 2010]. The model results were found to successfully
explain the measured dip [Hynek and Phillips, 2008] and inferred deposition rate [Lewis et al.,
2008] of the deposits. Deposits are also predicted within the Valles Marineris canyons, where
large sulfate-rich interior layered deposits are observed [Murchie et al., 2009].
Predicted
deposits in topographic lows in the northern lowlands and large impact basins may be obscured
beneath younger volcanic, sedimentary, and aeolian cover.
Some support for ancient
hydrological activity in the lowlands comes from recent observations of hydrated phyllosilicate
outcrops exposed by craters in the northern lowlands [Carter et al., 2010], and evidence for mud
volcanism possibly arising from a buried volatile-rich layer in Acidalia Planitia [Oehler and
Allen, 2010].
While the previous groundwater models considered the time evolution of the
hydrological cycle for a fixed set of environmental conditions, they did not address the
hydrological evolution in the face of an evolving climate on early Mars. Building on the success
of the earlier work in explaining the salient features of the late Noachian to early Hesperian
sedimentary record, we now investigate the temporal evolution of the hydrological cycle
throughout early Mars history.
4.2. Effect of the total water inventory: Wet and arid hydrological regimes
From a groundwater hydrology perspective, the hydrological state of the planet is
determined primarily by the total water inventory available to the hydrologic system relative to
the storage capacity of the global aquifer system, which is established in the models by the
assumed initial mean water table depth below the surface (initialized at a constant depth prior to
hydrological equilibration). This hydrologically available water inventory represents only that
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portion of the total water inventory that directly takes part in the hydrological cycle at any one
time. The previous study [Andrews-Hanna et al., 2010] assumed a single constant value for the
water inventory, for which the model predictions were found to be in agreement with the
observed distribution of sulfate deposits. However, the hydrologically available water inventory
of Mars is poorly constrained, and likely experienced significant periodic and secular changes
over Mars history. A suite of global hydrological models were run with different assumed initial
mean water table depths, ranging from 200 m to 1000 m. The models were run for 100 Myr to
achieve hydrological equilibrium without any sedimentary deposition, and then run for an
additional 50 Myr while tracking the evolving groundwater flux to the surface and sedimentary
deposit thickness (Figure 3). This set of models assumed arid conditions leading to evaporite
formation over the full range of initial mean water table depths and precipitation rates, an
assumption we will break with in section 5.
Models initialized with different initial mean water table depths produce substantially
different outcomes. The strongest constraint on the nature of the hydrological cycle comes from
the observed distribution and thickness of sulfate deposits formed in the Late Noachian to Early
Hesperian. These deposits are localized primarily within Meridiani Planum and the surrounding
Arabia Terra region, the Valles Marineris canyons, and the chaos regions at the sources of the
outflow channels. The predicted extent of the deposits agrees best with the observed distribution
for models with an initial mean water table depth of ~600 m (Figure 3g-i).
For an initial mean water table depth of 200 m, corresponding to a greater hydrologically
available water inventory, the water table intersects the surface throughout the low latitude
precipitation belt as well as within the northern lowlands and large impact basins (Figure 3a-c).
If all groundwater is assumed to evaporate immediately upon reaching the surface, this leads to
15
the prediction of widespread evaporite-cemented deposits covering much of the surface, in
conflict with their observed extent.
The shallow water table and short path lengths of
groundwater flow result in rapid cycling of water between the subsurface and the atmosphere,
driving high precipitation rates.
The predicted equatorial precipitation rate in hydrologic
equilibrium prior to the initiation of sedimentation is 12.1 mm/year, compared to 0.13 mm/year
for an initial mean water table depth of 600 m (Figure 4). In contrast, models with a lower
hydrologically available water inventory (e.g., initial mean water table depth of 1000 m) predict
the water table to lie deep beneath the surface throughout both the southern highlands and most
of Arabia Terra, resulting in minimal sedimentary deposition in Meridiani Planum and its
surroundings (Figure 3m-o). Groundwater reaches the surface and evaporates primarily within
the large impact basins and in the northern lowlands, and the precipitation rate is only 0.021
mm/year (Figure 4).
These models reveal two end-member regimes of global-scale water cycling. For lower
total water inventories, Mars is in the “arid hydrological regime”, in which the water table lies
deep beneath the surface over most of the planet and the precipitation rate is limited by the rate at
which deep groundwater flow supplies water to the surface. As the total water inventory is
increased, the system enters the “wet hydrological regime” in which the water table reaches the
surface throughout most of the low latitude precipitation belt, and the precipitation rate increases
asymptotically. In the wet regime models, the equilibrium storage capacity of the low latitude
aquifers is exceeded, so that the precipitation falls primarily on a saturated surface and the excess
water continues to circulate through the climate system. While there is a dramatic difference
between the hydrological behavior of Mars under wet and arid conditions, the transition between
the two regimes is gradational rather than discrete (Figure 4).
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The high precipitation rates and the saturation of the surface in the wet hydrological
regime violate the arid assumption in the models, and the precipitation would lead to runoff and
ponding. With abundant water available at the surface, the rates of evaporation and precipitation
would be dictated by the climate system [e.g., Richardson et al., 2007; Soto et al., 2010] rather
than the groundwater system. The water table would lie at or near the surface over most of the
planet, causing the groundwater hydrology to be dominated by short wavelength flow in local
topographic basins [Grimm and Harrison, 2003]. The widespread evaporites predicted by the
models as a consequence of the arid assumption (Figure 3b) would be replaced by fluvial erosion
and ponding, dictated by the combination of the climatically-controlled distribution of
precipitation and the groundwater flow patterns.
As the total water inventory is increased further, the wet hydrological regime would
approach the present-day terrestrial hydrological cycle. The total water inventory on the Earth
greatly exceeds the storage capacity of the crustal aquifers. The largest reservoir of terrestrial
water is in the oceans, with less than 1% contained within aquifers [Demming, 2002]. As a
result, there is at all times a large supply of water in direct communication with the Earth’s
atmosphere, and the rates of precipitation and evaporation are dictated by the climate system
rather than being limited by the rate of groundwater flow. Whether early Mars ever possessed
oceans or a truly Earth-like hydrological system remains an open question.
The model-predicted precipitation rates are likely lower bounds. These models assume
that all of the precipitation infiltrates the surface (where it is not saturated) and contributes to
recharging the deep aquifers. Thus, the precipitation rate in the models reflects only that part of
the hydrological cycle involving exchange with the deep subsurface, with no explicit
representation of runoff and ponding followed by evaporation prior to infiltration. Inclusion of a
17
surface hydrological cycle would increase the actual precipitation rates significantly.
In
particular, the high precipitation rates in the wet regime would lead to runoff and ponding of a
significant fraction of the precipitation. This surface reservoir of water would drive higher rates
of precipitation [Soto et al., 2010] and a more vigorous hydrological cycle than can be
represented in these groundwater hydrology models without an explicit representation of the
atmospheric component of the hydrological cycle. The actual precipitation rates in the wet
regime would be determined by the climate system rather than the groundwater hydrology.
Similarly, during the arid regime a significant fraction of the precipitation may evaporate prior to
infiltration, increasing the actual precipitation rate relative to the model value. For example, if
only 20% of the precipitation infiltrated the surface to reach the deep aquifers, the actual
precipitation rates would be a factor of 5 higher than predicted by the models.
4.3. Hydrological controls on the distribution of valley networks
Just as the predicted regions of groundwater upwelling in the arid regime match the
observed distribution of sulfates, the predicted distribution of near-surface groundwater during
the wet regime with a greater available water inventory shows some correlation with the
observed distribution of valley networks. The models predict a shallow water table in the low
latitude precipitation belt, with a much deeper water table in high southern latitudes resulting
from the lack of precipitation-induced recharge at high latitudes and the presence of the Hellas
basin acting as a hydrological sink. While this contrast between low and high latitudes is
imposed in the models by the assumed precipitation distribution, the models also predict
significant longitudinal differences in the mid-latitudes, breaking with the longitudinal symmetry
of the imposed zonal precipitation belt.
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In the southern mid-latitudes, the water table lies much deeper beneath the surface
surrounding the Hellas impact basin, while lying closer to the surface in the vicinity of Tharsis
(e.g., Figure 3d). As a result of its great depth, Hellas acts as a large hydrological sink, drawing
down the water table in the surroundings. The imposed low-latitude recharge belt over the
northern half of the basin results in an asymmetric drawdown cone towards the south. In
contrast, the high topography of Tharsis drives groundwater flow southwards into the
surrounding highlands, pushing the water table closer to the surface south of Tharsis. This largescale pattern in the distribution of shallow groundwater is in first order agreement with the
observed distribution of valley networks (Figure 1a) [Carr, 1995; Hynek and Phillips, 2003;
Stepinski and Collier, 2004; Hynek et al., 2010]. While the northern edge of the valley network
distribution is imposed by the dichotomy boundary and the resurfacing of the northern lowlands,
the southern edge follows an approximate great-circle path dipping southwards near Tharsis and
northwards near Hellas [Mutch et al., 1976].
The southern edge of the valley network
distribution approximately coincides with the transition from a shallow water table in the low
latitudes to a deep water table in the mid- to high-latitudes.
This similarity suggests that the distribution of groundwater may exert some control over
the formation of the valley networks, as might be expected given the importance of base flow
from groundwater to rivers and streams on the Earth [Demming, 2002]. However, the specific fit
of the valley networks from recent high resolution mapping [Hynek et al., 2010] to the predicted
regions of shallow water table is only approximate, suggesting that other processes likely also
exerted a significant control over valley network formation, including spatial variations in the
rate of precipitation on the surface [Soto et al., 2010].
19
4.4. Implications for the long-term hydrologic and climatic evolution of Mars
We suggest that the wet and arid hydrological regimes map approximately onto the
Noachian and late Noachian-early Hesperian periods, respectively. Throughout much of the
Noachian, the widespread valley networks, high erosion rates, and evidence for phyllosilicate
formation suggests abundant near-surface water and elevated precipitation rates throughout the
low latitudes. The decrease in erosion rates [Golombek et al., 2006], transition in valley network
morphology [Baker and Partridge, 1986; Harrison and Grimm, 2005], and ultimate cessation of
widespread valley network formation [Fassett and Head, 2008] in the Late Noachian is
consistent with the dramatic decrease in precipitation rates and the drop in the water table
predicted for a wet to arid hydrological transition (Figures 3 and 4).
Similarly, the geochemical change from widespread phyllosilicate formation to localized
sulfate deposition [Bibring et al., 2006] would have been a natural outcome of the wet to arid
hydrological transition. During much of the Noachian, the abundance of low salinity, nearneutral pH, meteoric rainwater and shallow groundwater would encourage widespread alteration
of the primary igneous mineralogy to phyllosilicates. After the hydrological transition, the
precipitation would rapidly infiltrate the arid surface over most of the planet, recharging aquifers
deep beneath the surface without prolonged interaction with the near-surface crust. However, in
a few regions, that coincide with the locations of observed sulfate deposits, this deep
groundwater would reach the surface after flowing long distances in the subsurface.
This
upwelling groundwater would have had ample time to equilibrate with the aquifer host rocks and
acquire a high solute concentration. Upon reaching the photochemically oxidized shallow
subsurface, the fluids would develop a low pH and high concentration of sulfates [Burns, 1993;
Burns and Fisher, 1993; Hurowitz et al., 2010]. Oxidation of the near-surface materials and
20
fluids would have been encouraged by physical mixing of the playa deposits within dunes which
would have enabled atmospheric and photolytic oxidation to penetrate to greater depths, and
fluctuations in the height of the water table which would have allowed alternating oxidation of
the near-surface sediments and fluid-sediment interaction. Laboratory experiments and
geochemical models in which basaltic weathering fluids are evaporated under oxidizing
conditions successfully predict the observed mineralogy at Meridiani, and further show a
decreasing pH with evaporitic concentration [Tosca et al., 2005]. The surface geochemistry in
regions of groundwater upwelling would be dominated by the chemistry of the upwelling brines,
with evaporation leading to localized precipitation of sulfate minerals, including jarosite [Burns,
1993].
Previous studies suggested that the geochemical transition from phyllosilicate to sulfate
deposition may have been triggered by an increase in Tharsis outgassing in the Late Noachian
[Bibring et al., 2006]. However, Tharsis outgassing alone fails to explain the change from
broadly distributed phyllosilicates to locally concentrated sulfates within a few isolated regions
[Bibring et al., 2006; Mustard et al., 2008b]. Layered deposits that appear to be genetically
related to the Meridiani sulfate deposits extend to the eastern edge of Arabia Terra [AndrewsHanna et al., 2010; Zabrusky and Andrews-Hanna, 2010], a distance of more than 5000 km from
the edge of Tharsis. More than half of the planet lies within this distance from Tharsis, and yet
sulfate deposits outside of Tharsis are largely isolated to locations in Meridiani Planum and
Arabia Terra.
Tharsis outgassing also fails to explain the timing of the sulfate formation. Tharsisinduced tectonism peaked during the Noachian [Anderson et al., 2001]. Tharsis outgassing
would thus have been active throughout the Noachian, much of which was dominated by
21
phyllosilicate rather than sulfate formation. Volcanic outgassing would have also been a
significant source of CO2 and H2O to the early martian atmosphere [Phillips et al., 2001], and the
release of sulfur and other greenhouse gasses has been invoked to explain the warm and wet
conditions on early Mars during the period of phyllosilicate formation [Halevy et al., 2007;
Johnson et al., 2008]. Tharsis outgassing cannot simultaneously explain both the warm and wet
conditions during the era of phyllosilicate alteration and valley network formation, and the later
transition to arid conditions and sulfate deposition. While Tharsis outgassing was likely an
important contributor of sulfur to the atmosphere and hydrosphere of early Mars, we suggest that
the transition between phyllosilicate alteration and sulfate deposition in the Late Noachian and
the specific distribution of sulfates are the results of a hydrologic and climatic transition driven
by a decrease in the hydrologically available global water inventory relative to the storage
capacity of the crustal aquifers.
4.5. Water loss mechanisms and the hydrological transition
The wet to arid hydrological transition corresponds to a change in the initial mean water
table depth from approximately 200 to 600 m, resulting in a transition from a saturated nearsurface throughout the low latitudes to a focusing of hydrological activity at Meridiani Planum
and Arabia Terra. This corresponds to a net loss of a global equivalent layer (GEL) of ~60 m of
water, assuming a mean near-surface porosity of 0.15 [Hanna and Phillips, 2005]. Such a
change could be brought about by either decreasing the total water inventory, or by increasing
the storage capacity of the crustal aquifers or other storage reservoirs.
Evidence for a decrease in the total water inventory of Mars is found in the elevated D/H
ratios in the martian atmosphere, interpreted as resulting from the erosion of atmospheric water
22
by solar wind sputtering [Yung et al., 1988; Donahue, 1995; Jakosky and Jones, 1997]. Impact
erosion of the atmosphere would have also contributed significantly to the loss of water [Melosh
and Vickery, 1989]. The combined effects of solar wind sputtering and impact erosion may have
eroded 95-99% of the early Martian atmosphere since the onset of the geologic record, with the
vast majority occurring during the early Noachian [Brain and Jakosky, 1998]. Lesser amounts of
atmospheric water loss are possible if the elevated deuterium concentration in Martian water
were due in part to a greater cometary contribution to the primordial water inventory of Mars
relative to the Earth [Lunine et al., 2003]. In section 5.1, we show that the loss rates due to solar
wind stripping and impact erosion combined with estimates of the present day water inventory
predict the loss of a GEL of ~80 m of water during the late Noachian and early Hesperian
epochs, which is sufficient to trigger a wet to arid hydrological transition.
Alternatively, a number of mechanisms exist for increasing the total storage capacity of
martian water reservoirs, which would be accompanied by a drop in the water table and could
trigger a wet-arid hydrological transition.
The storage capacity of the aquifers could be
increased by an increase in porosity due to continued impact-induced brecciation of the surface.
An increase in the porosity of the top 5 km by only 0.01 could trigger a wet to arid hydrological
transition. Water can also be removed from the active hydrological system by sequestration
within the polar caps and the high latitude ground ice as the climate cooled. It is not known
whether the polar caps on early Mars under different pressure, temperature, and humidity
conditions would have been larger or smaller than their present size, but they nevertheless
constitute a possible reservoir for increased storage of water as ice. The present-day south polar
cap and layered deposits are volumetrically dominated by water ice [Zuber et al., 2007] and are
estimated to contain a GEL of 11 m of water [Plaut et al., 2007].
23
Assuming flat basal
topography beneath the north polar layered deposits [Phillips et al., 2008], this repository
contains a GEL of ~5 m of water. The near-surface high latitude regions today contain also a
significant fraction of ground ice [Feldman et al., 2004]. The top 1 km of the crust pole-ward of
60° S latitude could contain a GEL of ~6.5 m of water, assuming a mean fractional ice content of
10%. Freezing or melting of north polar permafrost will not significantly change the total water
storage, since its location at low elevation would result in this region being water saturated under
warm conditions, and the replacement of water with ice does not significantly change the total
storage. These cryosphere reservoirs add up to the potential to change the total storage of water
as ice by a 22 m GEL of water, which falls short of the volume required to induce a wet to arid
transition but may have played a prominent role in short-term forcing of the hydrological cycle
as discussed in section 5.
While it is difficult to place firm bounds on the loss of water or increase in storage
capacity that can be attributed to any one mechanism, it is clear that the sum total of all
mechanisms is more than sufficient to account for the 60 m GEL loss or storage of water
necessary to induce the wet-arid hydrological transition in the late Noachian. The net loss of
water from Mars over time is supported by both geomorphic evidence for a wetter surface on
early Mars and isotopic evidence for water loss from the atmosphere. The model results and
interpretations above suggest that the observed geomorphic and geochemical evidence for the
hydrologic and climatic evolution of Mars can be understood in terms of a wet to arid
hydrological transition in the late Noachian driven by this net loss of water. While the specific
loss history is poorly constrained, one scenario for the evolving water inventory and its
hydrological ramifications is explored in detail in section 5.
24
5. Secular, episodic, and periodic variability of the hydrologic cycle
5.1. Short and long-term evolution of the available water inventory
Based on the evidence for both the secular evolution and shorter-term perturbations to the
hydrologic and climatic cycle described in section 2, and the sensitivity of the hydrological cycle
to variations in the available water inventory demonstrated in section 4, we now investigate in
more detail a specific scenario for the temporal evolution of the hydrology of early Mars. We
first generate a simplified scenario for the evolution of the hydrologically available water
inventory that reproduces qualitatively and at least semi-quantitatively the magnitudes and
timescales of the key processes at work. At present, there are no firm quantitative constraints on
the temporal evolution of the martian water inventory, though numerous studies have
investigated the various processes thought to have played a role. We synthesize the results of
these studies into a quantitative representation of the evolving water inventory, including secular
loss to solar wind stripping and impact erosion, and the changing storage of water in the
cryosphere in response to orbital forcing. This scenario is not meant to be a unique predictor of
the changes in water inventory, but rather to serve as a physically plausible proxy in order to
enable an investigation of the hydrological ramifications.
We first consider the secular evolution of the total water inventory, driven by loss over
time to solar wind stripping and impact erosion of the atmosphere. These processes both act in a
fractional sense on the amount of water in direct contact with the atmosphere at any one time. In
order to construct a time series of the change in water inventory, we take the present-day
inventory of an estimated 29 m GEL of water within the polar caps and near-surface ground ice
from the previous section (including the ground ice in the northern high latitudes) as
representative of the volume in contact with the atmosphere in the present epoch. The present-
25
day deep water inventory is unknown, but may be small due to the gradual desiccation of the
subsurface [Grimm and Painter, 2009] and is not currently in direct communication with the
atmosphere. We then reverse the loss rate to calculate the change in water inventory with time in
the past, assuming that any increase in the water inventory in the past relative to the present
remained in direct communication with the atmosphere.
While this approach is an
oversimplification, it allows the generation of an evolutionary scenario for the total water
inventory that is both quantitative and consistent with hypothesized loss mechanisms.
Water is lost to solar wind stripping at a constant fractional rate of 90% [Brain and
Jakosky, 1998].
This neglects the possible shielding effect of an early actively generated
magnetic field. Demagnetization of the giant impact basins suggests that the dynamo ceased by
the early to middle Noachian [Mohit and Arkani-Hamed, 2004; Lillis et al., 2008], prior to the
formation of much of the observed population of valley networks. Water is also lost to impact
erosion of the atmosphere at a rate that varies with time in proportion to the impact flux [Melosh
and Vickery, 1989]. Combining the impact and solar wind erosion of the atmosphere, the
resulting evolution in the total water inventory yields a loss of 109.1 m GEL between 4.0 and 3.0
Ga, representing the middle Noachian through late Hesperian (Figure 5). During this time, an
80.4 m GEL is lost between 4.0 and 3.7 Ga, representing the middle and late Noachian and
bracketing the time of the hydrologic and climatic transition. This loss history is consistent with
the loss of a ~60 m GEL required between the onset of the geologic record and the late Noachian
in order to induce the hydrologic and climatic transition from wet to arid conditions.
Over shorter timescales, the evolution of the hydrologically available water inventory
was likely driven primarily by changes in the storage of water in the polar caps and high latitude
permafrost induced by the orbital evolution of Mars. Short-term climate change is driven
26
primarily by the 120 kyr obliquity cycle, with the maximum obliquity within this cycle
modulated on a longer 1.2 Myr timescale [Laskar et al., 2004].
This regular behavior is
overprinted by significant shifts in mean obliquity, commonly reaching mean values as high as
50° or as low as 10°. The evolution of the orbital parameters of Mars are reasonably well
constrained for the past ~20 Myr, but over longer timescales the behavior is chaotic and
unpredictable [Laskar et al., 2004]. It is impossible to uniquely determine the evolution of Mars’
obliquity and other orbital parameters over the past 4.5 Ga. However, the fundamental nature of
the periodic and chaotic variations in the orbital parameters is similar in multiple simulations of
the past 250 Ma. The 120 kyr obliquity cycle and its 1.2 Myr modulation persist through all
simulations, while chaotic shifts in mean obliquity lead to periods of sustained high and low
obliquity of variable duration. There is no indication that this general behavior would have
changed appreciably since the orbits of the giant planets were stabilized after the Late Heavy
Bombardment at 3.9 Ga [Gomes et al., 2005]. We adopt a single 250 Myr orbital simulation
from Laskar et al. [2004] (solution 301003BIN_A.P001, available on the web at
http://www.imcce.fr/Equipes/ASD/insola/mars/mars.html), as representative of the periodic and
chaotic changes in orbital parameters. This simulation includes long periods of stability at both
high and low obliquity, as well significant shorter obliquity excursions.
We next relate this orbital evolution to the changing storage of water as ice in the
cryosphere. Conditions on early Mars may have been similar to those on the Earth today, in
which the total volume of water stored as ice in the polar caps, glaciers, and permafrost of the
Earth is highly sensitive to changes in climate driven by orbital Milankovitch cycles [Crowley
and Kim, 1994; Huybers and Wunsch, 2005]. The specific climatic conditions that prevailed on
Mars in the Noachian and Hesperian are unknown, as are the conditions that governed the
27
stability of the polar caps and cryosphere at that time. Nevertheless, the stability of the presentday polar caps and cryosphere have been shown to be highly sensitive to changes in the
latitudinal distribution of insolation driven by the orbital evolution [Mellon and Jakosky, 1995;
Levrard et al., 2007]. The stability of the north polar layered deposits has been parameterized as
a function of the orbital parameters for present day Mars [Levrard et al., 2007]. The polar ice
loss is primarily a function of the insolation at the summer solstice, while the polar ice gain is
primarily a function of obliquity [Levrard et al., 2007]. The south polar layered deposits appear
to be more stable than the north, though the specific dependence of the cap stability on the orbital
evolution has not been investigated. As a first order approximation, we use the stability
conditions for the present-day north polar layered deposits as a function of obliquity and summer
solstice insolation as a proxy for the stability of both polar caps and the permafrost on early
Mars. While this approach is not strictly valid for the higher atmospheric pressure, temperature,
and humidity likely on early Mars, it provides us with a simple means of representing the
sensitivity of the storage of ice within the cryosphere on the orbital evolution and must suffice
until future climate models provide more firm constraints on the early cryosphere and
hydrosphere evolution.
This approach neglects the possibility of the redeposition of ice in the low latitudes.
Under the present cold climatic conditions, ground ice becomes more stable in the low to mid
latitudes during periods of high obliquity while liquid water is everywhere unstable, and
obliquity cycles primarily redistribute ice between the polar caps and ground ice [Mellon and
Jakosky, 1995]. Under warmer climate conditions, we expect a significant fraction of the ice
released from the poles at high obliquity to enter into the hydrological cycle, as occurs on Earth.
Periods of high obliquity decrease the temperature contrast between the equator and poles. If the
28
global mean temperature was at or above the freezing point, then polar warming at high obliquity
would likely lead to release of water to the hydrosphere rather than ice deposition in the low to
mid latitudes, analogous to the sea level rise during interglacial periods triggered in part by high
obliquity on the Earth [Crowley and Kim, 1994]. The polar cap stability models implemented
here [Levrard et al., 2007] are specifically for the case of exchange with the atmosphere, and do
not include the effects of polar basal melting [Clifford, 1993; Clifford and Parker, 2001]. Polar
basal melting associated with changes in obliquity would lead to short-lived groundwater
mounds beneath the polar caps following excursions to high obliquity and would diminish the
hydrological response to short-term forcing, but would not alter the long-term behavior of the
system.
The parameterization of polar cap stability from Levrard et al. [2007] is applied to the
orbital evolution scenario from Laskar [2004] to construct a representative 250 Myr time series
of the obliquity, insolation at summer solstice, and the resulting change in water storage in the
polar caps and cryosphere (∆w; Figure 6). The maximum polar cap volumes were set equal to
those of the present-day caps, though larger polar caps may have been possible. The imposition
of this upper bound is necessary to keep the polar caps from reaching arbitrarily large sizes at
low obliquity, which would likely be unstable to outwards viscous flow. This 250 Myr time
series is then reflected and repeated to generate a 1 Gyr continuous time series. This short-term
periodic and episodic forcing is superimposed over the secular loss of water due to solar wind
stripping and impact erosion of the atmosphere for the period of interest between 4.0 and 3.0 Ga
(model P001a; Figure 7a), spanning the middle Noachian through the late Hesperian epochs
[Hartmann and Neukum, 2001]. A second representation of the variation in the available water
inventory was generated by shifting the time series representing the orbital forcing of the
29
cryosphere storage by 250 Myr relative to the secular loss time series (model P001b; Figure 8a),
such that the shifts in mean obliquity and resulting changes in cryosphere storage occur at
different times relative to the evolution of the total water inventory.
The resulting representations of the change in hydrologically available water in Figures
7a and 8a provide reasonable representations of the possible effects of atmospheric loss and
orbital forcing on early Mars. We emphasize that these are not intended to be unique solutions
of the evolution of the water inventory, as such is beyond the reach of our current understanding
of early Mars. Rather, these are intended only to be plausible and self-consistent scenarios to
enable a hydrological study of the implications of the time evolution of the water inventory.
5.2. Modeling the Noachian-Hesperian hydrological evolution
The secular evolution and short-term perturbations to the hydrologically available water
inventory generated above were input into the hydrological model as forcing functions. As water
is cycled between the subsurface and atmosphere in the models through groundwater evaporation
and precipitation, some fraction is added or removed in each time step to match the requirements
of the applied changes in total water inventory due to the combined effects of atmospheric loss
and either cold-trapping of water in the cryosphere or release of water to the atmosphere and
hydrosphere from melting or sublimation of the cryosphere ice.
In addition to the relative change in total water inventory, it is necessary to establish a
reference point at which the total water inventory can be constrained. The initial mean water
table depth at the beginning of the simulation (representing Mars at 4.0 Ga) is set such that
Meridiani Planum and Arabia Terra are regions of localized groundwater upwelling at the
Noachian-Hesperian boundary at ~3.7 Ga. This is achieved for an initial mean water table depth
30
of approximately 200 m. Substantially greater or lesser values for the initial mean water table
depth would result in models in which groundwater does not ever reach the surface in Meridiani,
or the low latitude surfaces are saturated throughout the simulation, respectively.
The
hydrological model is run for 100 Myr until equilibrium is achieved, and then the 1 Gyr time
series representing the hydrological forcing function is applied to perturb the hydrologically
available water inventory beginning at a model time of 0 Myr.
The models include a simple representation of the different behavior of the system in the
wet and dry hydrological regimes. In the wet regime, runoff and ponding of water is likely, and
substantial evaporite deposits are not expected to form in the comparatively wet climate. In the
arid regime, low precipitation rates and groundwater fluxes are expected to lead to evaporation
of the groundwater upon reaching the surface, leading to the formation of evaporites and
evaporite-cemented sediments. While the results of section 4.2 reveal the transition between the
wet and arid hydrological regimes to be gradational rather than discrete, in order to simply
represent these two behaviors in this model we specify a threshold precipitation rate to define a
discrete boundary between the two regimes. Based on the results of the equilibrium models
(Figures 3 and 4), this threshold precipitation flux is set to 2×10-4 m/year, which corresponds to a
focusing of hydrological activity at locations of observed sulfate deposits. Higher precipitation
rates are assumed to result in fluvial activity and alteration of the surface to phyllosilicates, and
lower precipitation rates are assumed to result in arid conditions with evaporite formation at loci
of groundwater upwelling. While this threshold precipitation rate is lower than would typically
be expected to result in significant runoff and fluvial modification of the surface, the model
precipitation rates are lower bounds and only reflect that portion of the precipitation that leads to
direct infiltration, as discussed in section 4.2.
31
The hydrological model was run for 1 Gyr using the two scenarios for the changing water
inventory, representing the time period between 4.0 and 3.0 Ga (Figures 7a and 8a). Evaporitemediated deposition was allowed only at precipitation rates below the specified threshold. The
time evolution of the precipitation rate and growth of sedimentary deposits were tracked (Figures
7b and 8b). The mean rate of groundwater upwelling to the surface and the mean depth to the
water table as a function of time were calculated both over Meridiani Planum and the associated
etched terrain [Hynek, 2004], as well as over the entire Arabia Terra region, defined here as the
region bounded by the 0 and -2500 m elevation contours centered on 0°N 0°E (Figures 7b, c and
8b, c).
Global maps of the depth to the water table, deposit thickness, and groundwater
upwelling rate are presented at key times for model P001b (Figure 9).
5.3. Model results: Long-term evolution
Mars starts out in the wet hydrological regime in the beginning of the simulations, with a
saturated near-surface and maximum precipitation rates of 60 cm/year (model P001a; Figure 7b)
and 1 cm/yr (model P001b; Figure 8b). The difference in early precipitation rates is due to the
fact that model P001a transitions into a high obliquity phase with the resulting release of water
from the cryosphere into the hydrosphere early in the simulation. The water table is close to the
surface throughout the low to mid latitudes early in these simulations (e.g., model P001b at 50
Myr; Figure 9a), but evaporite formation and induration of sedimentary deposits is inhibited by
the wet climate conditions. In both models, fluvial erosion and phyllosilicate formation would be
expected to dominate throughout the first 100 to 200 Myr of model time. As water is lost due to
solar wind stripping and impact erosion of the atmosphere, the water table drops deeper beneath
the surface in many regions of the planet, and the precipitation rate drops (Figures 7b, c and 8b,
32
c). The secular loss of water alone would drive a permanent transition from wet to arid
conditions. However, the superimposed effects of orbital forcing result in a more complicated
transition.
A shift from either wet to arid or arid to wet conditions can be brought about by a
perturbation to the hydrologically available water inventory in response to a shift in mean
obliquity.
Mars is most susceptible to these chaotic obliquity shifts when the total water
inventory and precipitation rate are close to the threshold level. In model P001a (Figure 7), after
~110 Myr the total water inventory has dropped to the point at which changes in the mean
obliquity can drive temporary shifts from the wet to arid hydrological regime. In this simulation,
three short excursions from high to low obliquity result in wet-arid transitions, each lasting 2-4
Myr. These brief excursions in mean obliquity would have caused alternating periods of valley
network erosion and sulfate deposition, possibly leading to fluvial erosion of the sulfate deposits.
At 137 Myr elapsed model time, model P001a transitions into a state of low mean obliquity that
persists for 226 Myr, forcing an abrupt and stable hydrological transition from wet to arid
conditions. At this point the increased aridity would allow significant evaporite deposits to form
in loci of groundwater upwelling. The subsequent transition to high obliquity at 363 Myr in this
model is insufficient to cause a shift back to the wet regime as a result of the cumulative effect of
the continued secular loss of water to impact and solar wind erosion of the atmosphere.
In model P001b (Figure 8) a shift from low to high obliquity at 113 Myr reinforces the
prevailing wet hydrological regime, causing an increase in the precipitation rate and a rise of the
water table. The hydrological response to this release of water into the hydrosphere in this
scenario provides a possible explanation for the evidence that valley network formation may
have peaked in the Late Noachian [Howard et al., 2005; Irwin et al., 2005; Fassett and Head,
33
2008]. Later in this simulation, short excursions to low obliquity are sufficient to drive brief
episodes of arid conditions beginning at 140 Myr model time. These arid regime episodes
become more frequent as the total water inventory declines, until the model transitions
permanently to the arid regime at 212 Myr elapsed model time.
Sedimentary deposition commences when the models transition into the arid regime,
leading to the growth of evaporite-cemented sedimentary deposits in Meridiani Planum and
much of Arabia Terra (e.g., model P001b at 240 Myr; Figure 9d-f). The mean groundwater
upwelling rates in Meridiani Planum are higher than in the broader Arabia Terra region, since
much of the surface of Arabia Terra is unsaturated. Similarly, the mean depth to the water table
over Meridiani is less than that over all of Arabia Terra. Shortly after the transition to arid
regime conditions, the water table gradually rises to shallower depths beneath the surface in
Meridiani and Arabia Terra despite the continued secular loss of water. This is observed in
model P001a at 137-175 Myr (Figure 7c), and in model P001b at 212-248 Myr (Figure 8c). This
rise of the water table is a result of the gradual sedimentary infilling of the deepest craters and
other depressions within Meridiani and Arabia Terra, which allows the rise of the water table
throughout the region [Andrews-Hanna et al., 2010]. However, the water table later resumes its
drop to deeper levels below the surface as a result of the declining total water inventory.
The sedimentary deposition and diagenetic alteration of the deposits in Meridiani Planum
and Arabia Terra are related to the rate of groundwater upwelling and the depth to the water
table. Active upwelling of deep fluids to the surface under arid regime conditions will result in
the formation of evaporites and evaporite cemented sedimentary deposits. Fluctuations in the
depth to the water table may result in diagenesis of the deposits at depth, with periods of stability
at a particular water table depth leading to formation of a discrete diagenetic front (e.g., the
34
Whatanga contact observed by Opportunity [Grotzinger et al., 2005]). A significant drop of the
water table would leave the deposits exposed to aeolian erosion and deflation, possibly
explaining the observed unconformities in HiRISE images (Figure 2) as well as in the large
valley within the Meridiani deposits [Wiseman et al., 2010]. Alternatively, a significant increase
in the precipitation rate during the period of sulfate deposition may result in fluvial erosion of the
deposits.
Transitions to high mean obliquity and the associated release of water from the
cryosphere result in an abrupt shallowing of the water table and increase in the precipitation rate
during arid regime conditions (e.g., at ~370 Myr in model P001a; Figure 7c).
Similarly,
transitions to low mean obliquity result in an abrupt deepening of the water table.
Short
excursions in mean obliquity drive oscillations in the water table height with amplitudes of 100200 m. These chaotic changes in mean obliquity generate disequilibrium hydrologic responses
that can be observed in the mean depth to the water table if the obliquity stabilizes at its new
value after the transition. Each decrease in mean obliquity results in an abrupt increase in the
depth to the water table as more water is placed into storage in the cryosphere. This is followed
by a gradual shallowing of the water table to an intermediate depth over the next ~50 Myr (e.g.,
from 630-680 Myr in model P001a; Figure 7c) as the planet comes into hydrological equilibrium
with the lower available water inventory. This provides a measure of the mean hydrological
response time of the planet of ~50 Myr. While the hydrological cycle responds to forcing on
much shorter timescales than this, as will be seen in the next section, it only comes into
equilibrium with an applied forcing on this timescale.
The loss of water and gradual drop in the water table eventually brings to an end the
groundwater upwelling and sedimentary deposition in Meridiani and Arabia Terra after 190 Myr
35
and 200 Myr, respectively, in model P001a. In model P001b, hydrological activity in Meridiani
and Arabia Terra ceases after 180 and 400 Myr, respectively, following a general pattern of a
northwards shift in the loci of hydrological activity in this region (Figure 9d-f and g-i). In both
models, Arabia Terra experiences renewed activity during periods of high obliquity, as
deposition in the bordering northern lowlands allows the water table to rise further towards the
surface (e.g., after ~500 Myr in model P001a, and 750 Myr in model P001b). However, the water
table remains below the surface throughout Meridiani Planum in the latter parts of both
simulations.
Even during periods of low obliquity late in the simulation, hydrological activity in the
Valles Marineris canyons persists, due to their great depth relative to the surroundings (e.g.,
model P001b at 600 Myr; Figure 9m-o). This is consistent with the generally younger age of the
interior layered deposits within the canyons and chaos regions [Glotch and Christensen, 2005;
Flahaut et al., 2010] and their greater thickness in comparison with the Meridiani deposits.
Sedimentary deposition in the models is allowed to continue throughout the simulations
wherever there is a flux of groundwater to the surface. In actuality, a transition to cold climate
conditions sometime during the Hesperian likely brought an end to both the precipitationinduced aquifer recharge and the groundwater upwelling to the surface, setting the stage for
outflow channel formation during the Hesperian. However, the presence of sulfate deposits that
lie stratigraphically above chaos regions at the sources of outflow channels [Glotch and
Christensen, 2005] suggests that this transition to cold temperatures was not a simple abrupt and
irreversible change.
5.4. Model results: Short-term periodicity
36
In both simulations, the model behavior over 10-100 Myr timescales is characterized by
abrupt changes in the depth to the water table and the rate of groundwater upwelling, driven by
perturbations to the hydrologically available total water inventory in response to chaotic changes
in the mean obliquity. Over shorter timescales, the hydrology is dominated by the effects of the
120 kyr obliquity cycle and the modulation of the maximum obliquity with a 1.2 Myr period.
This short-term periodicity is observed in both the precipitation rate and the groundwater flux at
Meridiani (Figure 10). This hydrological periodicity could be expressed in the sedimentary
record through modulation of the layer thickness or strength due to either variations in the
precipitation rate, which would affect the supply of clastic material incorporated into the
deposits, or variations in the groundwater flux, which would affect the supply of solutes and the
degree of induration of the deposits.
The response of the aquifers to this short-term periodicity is limited by the hydrologic
diffusion timescale for subsurface flow. The timescale for regional hydrological equilibration
observed in the response to changes in mean obliquity in the previous section was ~50 Myr. On
a regional scale, much of the groundwater flows at depths of up to a km or more for distances of
100’s to 1000’s of km before reaching the surface in Meridiani Planum and Arabia Terra. For
the aquifer model of Hanna and Phillips [2005], the hydraulic diffusion timescale for subsurface
flow with a water table at 1 km depth over horizontal length scales of 100-1000 km is ~0.3-30
Myr. For a water table located 100 m below the surface over the same range of length scales, the
hydraulic diffusion timescale ranges from 0.04-4 Myr. This simple scaling analysis would
suggest that the large scale hydrology in regions with a particularly deep water table should be
unperturbed by the 120 kyr obliquity cycle, while regions with a shallow water table will be
more strongly influenced. However, while the water table remains at depth below the surface for
37
great distances, the aquifers experience precipitation-induced recharge throughout the low
latitudes, including Arabia Terra. As a result, the groundwater upwelling at Meridiani is sourced
from precipitation-induced recharge from all points between Meridiani and the hydraulic divide
between Arabia Terra and the Hellas impact basin. Due to the shallow aquifers in the vicinity of
the deposits and the range of flow path lengths that contribute to the groundwater upwelling,
even the short 120 kyr obliquity cycle is strongly expressed in the rate of groundwater upwelling.
During some portions of the orbitally driven hydrological evolution, a relatively constant
120 kyr periodicity is observed in both the precipitation and groundwater upwelling rates at
Meridiani (Figure 10g). During other periods, the 1.2 Myr modulation of the obliquity cycle is
strongly expressed in the hydrologic response (Figure 10h, i). These two hydrological behaviors
provide a possible explanation for the observation that some sedimentary deposits show a
uniform layering periodicity at HiRISE scale while others show layers bundled into packets of 10
[Lewis et al., 2008; Lewis et al., 2010]. The bundled layer packets have been correlated to the
120 kyr obliquity cycle and its 1.2 Myr modulation [Lewis et al., 2008], suggesting that the
individual layers in similar deposits with uniform periodicity may reflect forcing by the 120 kyr
obliquity cycle without substantial 1.2 Myr modulation.
Within the framework of this model, the pronounced 1.2 Myr modulation of the
hydrologic response arises primarily during periods of stable low (Figure 10b) or high (Figure
10c) mean obliquity. This appears to be in part an effect of the imposition of a maximum polar
cap size at low obliquity, and a minimum (zero) polar cap size at high obliquity. In times of
sustained low mean obliquity at values of ~20° (Figure 10b), the polar caps reach their maximum
size, and only experience significant loss during the periods of highest obliquity over the 1.2 Myr
modulation of the obliquity cycle. Similarly, in times of sustained high mean obliquity at values
38
of ~35° (Figure 10c), the polar caps disappear entirely and only experience regrowth at periods
of lowest obliquity during the 1.2 Myr modulation of the obliquity cycle. The more pronounced
1.2 Myr modulation of the precipitation and evaporation rates in Figure 10i is also attributable to
the more pronounced 1.2 Myr modulation of the obliquity cycle at this time (Figure 10c).
In actuality, the hydrologic and climatic cycle was likely much more complicated than
the simplified representation in this model, leaving open the possibility of other mechanisms for
modulating the layer periodicity.
Other factors related to climatic variability, including
variations in the supply of aeolian dust and sand [Lewis et al., 2010], may have contributed to the
observed layering periodicity as well. Nevertheless, these model results provide one possible
mechanism by which perturbations to the hydrologically available water inventory due to orbital
forcing can explain the observed periodicity and bundling of layers in sedimentary deposits on
Mars. Significantly, this work demonstrates that hydrologic and climatic forcing over 120 kyr
timescales would be expected to significantly affect the groundwater hydrology at the locations
of sedimentary deposition in Meridiani Planum and Arabia Terra as suggested by the
sedimentary record.
7. Conclusions and Discussion
There is abundant evidence for the presence of water on the surface of Mars early in the
planet’s history, and for the importance of groundwater in the hydrological cycle. We have used
groundwater hydrology models to provide a theoretical framework in which to understand and
interpret the observed record of water-related activity throughout the Noachian and early
Hesperian epochs, and to integrate the different lines of evidence into a coherent picture of the
global hydrologic and climatic evolution. The model results provide a mechanism for causing the
39
inferred geomorphic and geochemical transition in the late Noachian to early Hesperian, and
shed light on the factors controlling the distribution and timing of the formation of sulfates,
phyllosilicates, and valley networks. While there is significant uncertainty in many of the model
inputs, the resulting hydrological behavior is driven primarily by the large-scale topography of
Mars and the effects of short- and long-term changes in the hydrologically available water
inventory. The model results are not intended to provide a specific prediction of the actual time
evolution of the hydrologic cycle, but rather to provide a qualitative and semi-quantitative
representation of a possible hydrologic and climatic history that is built on our current
understanding of the key processes involved. In the context of this work, we suggest the
following scenario for the hydrologic and climatic evolution of Mars during the Noachian and
early Hesperian.
Early Mars possessed an active hydrological cycle, with deep groundwater flow driven
by a combination of low latitude precipitation, groundwater evaporation, and the long
wavelength topography. The nature of the hydrological cycle at any given time was determined
primarily by the hydrologically available total water inventory, which underwent long- and
short-term variations driven by the secular loss of water to impact and solar wind stripping, and
periodic and episodic changes in the volume of water stored as ice in the polar caps and
subsurface cryosphere induced by orbital forcing.
During the Noachian, a greater total water inventory fueled a more vigorous hydrological
cycle in what we term the wet hydrological regime. Mean precipitation rates were controlled by
the climatic redistribution of water, with significant surface and shallow subsurface reservoirs of
water in direct communication with the atmosphere. The high precipitation rates and shallow
water table throughout the low latitudes resulted in phyllosilicate weathering reactions in the
40
near-surface and erosion rates comparable to those in arid and semi-arid regions of the Earth
today. Wet conditions favored surface runoff and ponding over evaporite deposition, though
these were not explicitly included in the models. The first-order correlation of the distribution of
valley networks with regions predicted to be underlain by a shallow water table suggests that
groundwater may have played a role in controlling valley network formation.
The steady loss of water to impact and solar wind erosion triggered a shift in the
hydrological regime to arid conditions in the late Noachian. This transition required a loss of a
GEL of only ~60 m of water, which can be easily accounted for by estimated atmospheric loss
rates on early Mars. In the arid hydrological regime, the water table remained deep beneath the
surface throughout much of the low latitudes, with groundwater only intersecting the surface in a
few isolated locations, including the large impact basins and the northern lowlands. In this arid
hydrological regime, the precipitation rate was dictated by the rate of deep groundwater flow,
leading to a dramatic drop in precipitation and erosion rates.
At some point intermediate between the extreme wet and arid hydrological regimes,
Meridiani Planum and the surrounding Arabia Terra region emerged as one of the few regions of
presently exposed Noachian-aged crust in which the water table reached the surface. The long
path lengths of groundwater flow allowed ample time for equilibration of the fluids with the
basaltic aquifers, resulting in high salinity, sulfate-rich fluids that became acidic upon interacting
with the oxidized surface environment [Hurowitz et al., 2010]. The high ratio of deeply sourced
groundwater to meteoric water in regions of groundwater upwelling within a few key regions
resulted in evaporite deposition and cementation of aeolian sediments.
A steady flux of
groundwater to the surface in Arabia Terra sustained regional playa development in the absence
of a topographic basin, driven by the combination of the general low topography of Arabia Terra
41
relative to the highlands and the distinct breaks in slope separating Arabia Terra from the
southern highlands and northern lowlands [Andrews-Hanna et al., 2007]. As Mars transitioned
into this arid hydrological regime in the Late Noachian, higher resolution hydrological models
predict a sequence in which large craters within Arabia Terra first filled with evaporites and
evaporite-cemented sediments, which allowed the regional water table to rise towards the surface
resulting in broad regions of groundwater upwelling to fuel the playa formation at Meridiani
[Andrews-Hanna et al., 2010]. Continued loss of water eventually terminated hydrological
activity within Arabia Terra. Hydrological activity and groundwater-mediated cementation of
sedimentary deposits would have continued in Valles Marineris long after the water table had
dropped below the surface in Arabia Terra.
Superimposed over this secular evolution, episodic perturbations to the hydrologically
available total water inventory would have resulted from the change in storage of water as ice in
the polar caps and high latitude ground ice in response to chaotic changes in mean obliquity
[Laskar et al., 2004; Levrard et al., 2007]. This change in available water volume would have
resulted in episodic changes in the precipitation rates, water table depths, and flux of
groundwater to the surface. These episodic changes may explain the terminal epoch of enhanced
fluvial activity in the Late Noachian [Irwin et al., 2005] and the rapid cessation of valley network
activity at the end of the Noachian [Fassett and Head, 2008]. In this scenario, valley network
activity in the Middle Noachian was waning due to the secular loss of water with time, under low
obliquity conditions with increased storage of water as ice in the cryosphere. A shift to high
obliquity in the Late Noachian then triggered melting and sublimation of the high latitude ice
deposits, driving a sudden increase in the hydrologically available water inventory and a shift to
42
renewed wet conditions. A shift back to low obliquity could then have driven an equally abrupt
shift to arid conditions and sulfate formation.
Similar changes in mean obliquity in the Late Noachian to Early Hesperian would have
caused abrupt changes in the rate of groundwater upwelling and the depth to the water table in
Meridiani Planum and Arabia Terra, leading to sequences of groundwater upwelling and
sedimentation, water table retreat and erosion, and water table rise causing diagenetic
modification and renewed deposition. Alternately, an increase in precipitation during the period
of sulfate deposition may have led to fluvial erosion of the forming sedimentary deposits. Such
episodic changes may explain erosional unconformities expressed in HiRISE images of layered
sedimentary deposits, a large-scale erosional unconformity in northern Sinus Meridiani
[Wiseman et al., 2010], and evidence for a fluctuating water table and diagenetic episodes
expressed in the Meridiani deposits [Grotzinger et al., 2005; McLennan et al., 2005].
On shorter timescales, perturbations to the hydrological cycle driven by the 120 kyr
obliquity cycle and the 1.2 Myr modulation of that cycle resulted in similar periodicities in the
precipitation and groundwater upwelling rates in Meridiani and Arabia Terra, equivalent to
Milankovitch forcing of the Earth’s climate. Model results at different times show both a regular
120 kyr periodicity, as well as a 120 kyr periodicity that is modulated strongly by the 1.2 Myr
cycle. These model behaviors correlate with the observation of both sedimentary deposits with a
uniform periodicity at HiRISE scale [Lewis et al., 2010], as well as deposits in which the layer
periodicity is bundled into packets of 10 [Lewis et al., 2008].
Previous work has focused largely on the role of temperature changes in the climate
evolution of Mars.
The scenario developed here highlights instead the importance of the
changing availability of water in both the hydrological and climatic evolution. The decline in
43
valley network formation, the decrease in erosion rates, and the shift from phyllosilicate to
sulfate deposition can all be explained by a change in the available water inventory under warm
climate conditions. Changes in the mean surface temperature would have also exerted a
significant control on the rate of water cycling and the nature of hydrological activity on the
surface. Ultimately, the onset of cold climate conditions in the Late Hesperian trapped the
aquifers beneath a thick cryosphere, essentially halting the hydrologic cycle. Rather than a
simple transition from warm and wet to cold and dry conditions, we suggest that Mars underwent
a transition from warm and arid, to warm and hyper-arid conditions in the Late Noachian,
followed by a transition to cold and hyper-arid conditions in the Hesperian. Both the geologic
record and these model results show that these transitions would have been gradual and complex
rather than discrete and simple, but the decoupling of the temperature and moisture conditions is
an essential aspect of the hydrologic and climatic history of Mars.
Acknowledgements. We are grateful to Sandra Wiseman for comments on an early draft of the
manuscript, and to Tim Glotch for a thorough and thoughtful review. This work was supported
by a grant from the NASA Mars Data Analysis Program to J.C.A.-H.
44
Figures
Figure 1. Evidence for the global hydrological evolution of Mars from the distribution of (a)
valley networks [adapted from Hynek et al., 2010], (b) hydrated minerals, with phyllosilicates in
red, sulfates in blue, and other hydrated minerals in yellow [adapted from Bibring et al., 2006],
and (c) layered sedimentary deposits [adapted from Malin and Edgett, 2000].
45
Figure 2. Evidence in the sedimentary record for temporal variability in the hydrological cycle,
including rhythmic strata and stratigraphic unconformities. (a) Uniformly spaced rhythmic
bedding exposed on the floor of Danielson crater (8N, 353E; HiRISE image PSP_002733_1880).
(b) Multiple scales of cyclicity preserved within a sedimentary mound in Becquerel crater (22N,
352E; HiRISE image PSP_001546_2015).
Rhythmic beds several meters in thickness are
bundled into larger stratigraphic units at the scale of tens of meters. Roughly 10 beds comprise
each of the larger bundles, which may be linked to a similar ratio of frequencies in the martian
obliquity signal. (c) Truncation surface within cross-bedded eolianites at Meridiani Planum, as
seen
from
the
Opportunity
Rover
(Sol
278
Pancam
image
mosaic
from
http://pancam.astro.cornell.edu/). In this example, it is difficult to determine whether the exposed
truncation surface is evidence of a widespread deflationary episode in the Meridiani stratigraphy,
or simply a local scour surface. The exposed outcrop is roughly 7 meters thick in the vertical
direction. (d) Prominent angular unconformity within cyclically bedded sediments in a crater on
the north rim of the Schiaparelli basin (HiRISE image PSP_002508_1800).
(e) Angular
unconformity in Gale crater (HiRISE image PSP_009149_1750). The relatively large impact
46
crater preserved at this stratigraphic horizon is good evidence of a long depositional hiatus before
emplacement of the overlying strata.
47
Figure 3. Hydrological model outputs for different initial mean water table depths (wt),
representing different values of the hydrologically available water inventory. Panels show the
depth to the water table (left), predicted sedimentary deposit thickness after 50 Myr (center), and
distribution and rate of groundwater upwelling and evaporation after 50 Myr (right), for initial
mean water table depths ranging from 200 m (top) to 1000 m (bottom).
48
Figure 4. Predicted equatorial precipitation rate in balance with the rate of deep groundwater
flow prior to sedimentation for initial mean water table depths ranging from 200 m to 900 m.
The shaded bar at top schematically represents the transition from wet to arid conditions. The
arrow represents the initial mean water table depth for which the model results most closely
match the observed distribution of deposits in Meridiani and Arabia Terra.
49
Figure 5. Model scenario for the evolution of the change in total water inventory (∆w) in
contact with the atmosphere due to solar wind stripping and impact erosion over 4.5 Ga,
calculated by extrapolating the present water inventory backwards with time.
50
Figure 6. (a) Obliquity, (b) insolation at southern summer solstice (iss), and (c) change in
volume of water stored in the polar caps and subsurface cryosphere (∆w) over 250 Myr based on
the orbital evolution model P001 of Laskar et al. [2004] and the parameterization of the stability
of the north polar layered deposits of Levrard et al. [2007].
51
Figure 7. Results from a 1 Gyr simulation representing the effects of orbital forcing and secular
loss of water between 4.0 and 3.0 Ga for model P001a.
Panels show (a) change in
hydrologically-available total water inventory (∆w), (b) the evolving precipitation flux in
comparison with the mean groundwater upwelling rate within Meridiani Planum and all of
Arabia Terra, and (c) the mean depth to the water table within Meridiani Planum and Arabia
Terra.
52
Figure 8. Results from a 1 Gyr simulation representing the effects of orbital forcing and secular
loss of water between 4.0 and 3.0 Ga for model P001b, with the orbital component of the
hydrological forcing shifted by 500 Myr relative to model P001a in Figure 6. Panels show (a)
change in hydrologically-available total water inventory (∆w), (b) the evolving precipitation flux
in comparison with the mean groundwater upwelling rate within Meridiani Planum and all of
Arabia Terra, and (c) the mean depth to the water table within Meridiani Planum and Arabia
Terra. The vertical dashed lines mark the times at which the results are presented in map view in
Figure 9.
53
Figure 9. Predicted depth to the water table (left), deposit thickness (center), and groundwater
upwelling rate (right) during simulation P001b at 50, 240, 350, 390, and 600 Myr (see Figure 8).
54
Figure 10. Plots of the hydrological model results over 10 Myr intervals showing regular
periodic behavior due to the obliquity cycle (left) and a bundled periodicity due to the
modulation of the obliquity cycle on a 1.2 Myr timescale (center and right). The obliquity
models assumed to be driving the short term climatic forcing (top) and result in a perturbation to
the hydrologically available water inventory (middle). The perturbation to the water inventory
results in temporal variations in the equatorial precipitation rates, and the mean rates of
groundwater upwelling and evaporation in Meridiani Planum and Arabia Terra (bottom).
55
References.
Anderson, R. C., J. M. Dohm, M. P. Golombek, A. F. C. Haldemann, B. J. Franklin, K. L.
Tanaka, J. Lias, and B. Peer (2001), Primary centers and secondary concentrations of
tectonic activity through time in the western hemisphere of Mars, J. Geophys. Res.,
106(E9), 20563-20585.
Andrews-Hanna, J. C., and R. J. Phillips (2007), Hydrological modeling of outflow channels and
chaos regions, J. Geophys. Res., 112, E08001, doi:08010,01029/02006JE002881.
Andrews-Hanna, J. C., R. J. Phillips, and M. T. Zuber (2007), Meridiani Planum and the global
hydrology of Mars, Nature, 446, 163-166.
Andrews-Hanna, J. C., M. T. Zuber, R. E. Arvidson, and S. M. Wiseman (2010), Early Mars
hydrology: Meridiani playa deposits and the sedimentary record of Arabia Terra, J.
Geophys. Res., 115, E06002, doi:06010.01029/02009JE003485.
Arvidson, R. E., F. Poulet, R. V. Morris, J. F. Bell, S. W. Squyres, P. R. Christensen, G.
Bellucci, B. Gondet, B. L. Ehlmann, W. H. Farrand, R. L. Fergason, M. Golombek, J. L.
Griffes, J. Grotzinger, E. A. Guiness, K. E. Herkenhoff, J. R. Johnson, G. Klingelhofer,
Y. Langevin, D. Ming, K. Seelos, R. J. Sullivan, J. G. Ward, S. M. Wiseman, and M.
Wolff (2006), Nature and origin of the hematite-bearing plains of Terra Meridiani based
on analyses of orbital and Mars Exploration Rover data sets, J. Geophys. Res., 111,
E12S08, doi:10.1029/2006JE002728.
Baker, V. R. (1982), The Channels of Mars, 198 pp., University of Texas Press, Austin.
Baker, V. R., and J. B. Partridge (1986), Small martian valleys: Pristine and degraded
morphology, J. Geophys. Res., 84, 3561-3572.
Barnhart, C. J., A. D. Howard, and J. M. Moore (2009), Long-term precipitation and late-stage
valley network formation: Landform simulations of the Parana Basin, Mars, J. Geophys.
Res., 114, E01003, doi:01010.01029/02008JE003122.
Bibring, J.-P., Y. Langevin, J. F. Mustard, F. Poulet, R. Arvidson, A. Gendrin, B. Gondet, N.
Mangold, P. Pinet, F. Forget, and t. O. team (2006), Global mineralogical and aqueous
Mars history derived from OMEGA/Mars Express data, Science, 312, 400-404.
Brain, D. A., and B. M. Jakosky (1998), Atmospheric loss since the onset of the martian geologic
record: Combined role of impact erosion and sputtering, J. Geophys. Res., 103(E10),
22689-22694.
Burns, R. G. (1993), Rates and mechanisms of chemical weathering of ferromagnesium silicate
minerals on Mars, Geochim. Cosmochim. Acta, 57, 4555-4574.
Burns, R. G., and D. S. Fisher (1993), Rates of oxidative weathering on the surface of Mars, J.
Geophys. Res., 98(E2), 3365-3372.
Carr, M. H., and G. D. Clow (1981), Martian channels and valleys: Their characteristics,
distribution, and age, Icarus, 48, 91-117.
Carr, M. H. (1995), The martian drainage system and the origin of valley networks and fretted
channels, J. Geophys. Res., 100(E4), 7479-7507.
Carr, M. H., and F. C. Chuang (1997), Martian drainage densities, J. Geophys. Res., 102(E4),
9145-9152.
Carr, M. H., and M. C. Malin (2000), Meter-scale characteristics of martian channels and
valleys, Icarus, 146, 366-386.
Carter, J., F. Poulet, J.-P. Bibring, and S. L. Murchie (2010), Detection of hydrated silicated in
crustal outcrops in the northern plains of Mars, Science, 328, 1682-1686.
56
Clifford, S. M. (1993), A model for the hydrologic and climatic behavior of water on Mars, J.
Geophys. Res., 98(E6), 10973-11016.
Clifford, S. M., and T. J. Parker (2001), The evolution of the martian hydrosphere: Implications
for the fate of a primordial ocean and the current state of the northern plains, Icarus, 154,
40-79.
Craddock, R. A., and A. D. Howard (2002), The case for rainfall on a warm, wet early Mars, J.
Geophys. Res., 107(E11), 5111, doi:5110.1029/2001JE001505.
Crowley, T. J., and K.-Y. Kim (1994), Milankovitch forcing of the last interglacial sea level,
Science, 265, 1566-1568.
Demming (2002), Introduction to Hydrology, 468 pp., McGraw Hill, New York.
Di Achille, G., and B. M. Hynek (2010), Ancient ocean on Mars supported by global distribution
of deltas and valleys, Nature Geoscience, 3, 459-463.
Donahue, T. M. (1995), Evolution of water reservoirs on Mars from D/H ratios in the
atmosphere and crust, Nature, 374, 432-434.
Fassett, C. I., and J. W. Head (2007), Layered mantling deposits in northeast Arabia Terra, Mars:
Noachian-Hesperian sedimentation, erosion, and terrain inversion, J. Geophys. Res., 112,
E08002, doi:08010.01029/02006JE002875.
Fassett, C. I., and J. W. Head (2008), The timing of martian valley network activity: Constraints
from buffered crater counting, Icarus, 195, 61-89.
Feldman, W. C., T. H. Prettyman, S. Maurice, J. J. Plaut, D. L. Bish, D. T. Vaniman, M. T.
Mellon, A. E. Metzger, S. W. Squyres, S. Karunatillake, W. V. Boynton, R. C. Elphic, H.
O. Funsten, D. J. Lawrence, and R. L. Tokar (2004), Global distribution of near-surface
hydrogen on Mars, J. Geophys. Res., 109, E09006, doi:09010.01029/02003JE002160.
Fergason, R. L., and P. R. Christensen (2008), Formation and erosion of layered materials:
Geologic and dust cycle history of eastern Arabia Terra, Mars, J. Geophys. Res., 113,
E12001, doi:12010.11029/12007JE002973.
Flahaut, J., C. Quantin, P. Allemand, and P. Thomas (2010), Morphology and geology of the
ILD in Capri/Eos Chasma (Mars) from visible and infrared data, Icarus, 207, 175-185.
Fueten, F., R. Stesky, P. MacKinnon, E. Hauber, T. Zegers, K. Gwinner, F. Scholten, and G.
Neukum (2008), Stratigraphy and structure of interior layered deposits in west Candor
Chasma, Mars, from High Resolution Stereo Camera (HRSC) stereo imagery and derived
elevations, J. Geophys. Res., 113, E10008, doi:10010.11029/12007JE003053.
Gendrin, A., N. Mangold, J.-P. Bibring, Y. Langevin, B. Gondet, F. Poulet, G. Bonello, C.
Quantin, J. Mustard, R. Arvidson, and S. LeMouelic (2005), Sulfates in martian layered
terrains: The OMEGA/Mars Express view, Science, 307, 1587-1591.
Glotch, T. D., and P. R. Christensen (2005), Geologic and mineralogic mapping of Aram Chaos:
Evidence for a water-rich history, J. Geophys. Res., 110, E09006,
doi:09010.01029/02004JE002389.
Glotch, T. D., J. L. Bandfield, P. R. Christensen, W. M. Calvin, S. M. McLennan, B. C. Clark, A.
D. Rogers, and S. W. Squyres (2006), Mineralogy of the light-toned outcrop at Meridiani
Planum as seen by the Miniature Thermal Emission Spectrometer and implications for its
formation, J. Geophys. Res., 111, E12S03, doi:10.1029/2005JE002672.
Glotch, T. D., and A. D. Rogers (2007), Evidence for aqueous deposition of hematite- and
sufate-rich light-toned layered deposits in Aureum and Iani Chaos, Mars, J. Geophys.
Res., 112, E06001, doi:06010.01029/02006JE002863.
57
Goldspiel, J. M., and S. W. Squyres (2000), Groundwater sapping and valley formation on Mars,
Icarus, 148, 176-192.
Golombek, M. P., J. A. Grant, L. S. Crumpler, R. E. Arvidson, J. F. Bell, C. M. Weitz, R. J.
Sullivan, P. R. Christensen, L. A. Soderblom, and S. W. Squyres (2006), Erosion rates at
the Mars Exploration Rover landing sites and long-term climate change on Mars, J.
Geophys. Res., 111, E12S10, doi:10.1029/2006JE002754.
Gomes, R., H. F. Levison, K. Tsiganis, and A. Morbidelli (2005), Origin of the cataclysmic Late
Heavy Bombardment period of the terrestrial planets, Nature, 435, 466-469.
Grimm, R. E., and K. H. Harrison (2003), A parochial view of groundwater flow on Mars, Lun.
Plan. Sci., 34, Abstract 2053.
Grimm, R. E., and S. L. Painter (2009), On the secular evolution of groundwater on Mars,
Geophys. Res. Lett., 36, L24803, doi:24810.21029/22009GL041018.
Grotzinger, J. P., R. E. Arvidson, J. F. Bell, W. Calvin, B. C. Clark, D. A. Fike, M. Golombek,
R. Greeley, A. Haldemann, K. E. Herkenhoff, B. L. Jolliff, A. H. Knoll, M. Malin, S. M.
McLennan, T. Parker, L. Soderblom, J. N. Sohl-Dickstein, S. W. Squyres, N. J. Tosca,
and W. A. Watters (2005), Stratigraphy and sedimentology of a dry to wet eolian
depositional system, Burns formation, Meridiani Planum, Mars, Earth Planet. Sci. Lett.,
240, 11-72.
Halevy, I., M. T. Zuber, and D. P. Schrag (2007), A sulfur dioxide climate feedback on early
Mars, submitted to Science.
Handford, C. R. (1991), Marginal marine halite: Sabkhas and salinas, in Evaporites, Petroleum,
and Mineral Resources, edited by J. L. Melvin, Elsevier, New York.
Hanna, J. C., and R. J. Phillips (2005), Hydrological modeling of the Martian crust with
application to the pressurization of aquifers, J. Geophys. Res., 110, E01004,
doi:01010.01029/02004JE002330.
Hanna, J. C., and R. J. Phillips (2006), Tectonic pressurization of aquifers in the formation of
Mangala and Athabasca Valles, Mars, J. Geophys. Res., 111, E03003,
doi:03010.01029/02005JE002546.
Harrison, K. P., and R. E. Grimm (2005), Groundwater-controlled valley networks and the
decline of runoff on early Mars, J. Geophys. Res., 110(E12), E12S16,
doi:10.1029/2005JE002455.
Hartmann, W. K., and G. Neukum (2001), Cratering chronology and the evolution of Mars,
Space Science Reviews, 96, 165-194.
Hoke, M. R., and B. M. Hynek (2009), Roaming zones of precipitation on ancient Mars as
recorded in valley networks.
Howard, A. D., J. M. Moore, and R. P. Irwin (2005), An intense terminal epoch of widespread
fluvial activity on early Mars: Valley network incision and associate deposits, J.
Geophys. Res., 110, E12S14, doi:10.1029/2005JE002459.
Hurowitz, J. A., W. W. Fischer, N. J. Tosca, and R. E. Milliken (2010), Origin of acidic surface
waters and the evolution of atmospheric chemistry on early Mars, Nature Geoscience,
published online 4 April 2010, doi:2010/1038/ngeo2831.
Huybers, P., and C. Wunsch (2005), Obliquity pacing of the late Pleistocene glacial terminations,
Nature, 434, 491-494.
Hynek, B. M., and R. J. Phillips (2003), New data reveal mature, integrated drainage systems on
Mars indicative of past precipitation, Geology, 31(9), 757-760.
58
Hynek, B. M. (2004), Implications for hydrologic processes on Mars from extensive bedrock
outcrops throughout Terra Meridiani, Nature, 431, 156-159.
Hynek, B. M., and R. J. Phillips (2008), The stratigraphy of Meridiani Planum, Mars, and
implications for the layered deposits' origin, Earth Planet. Sci. Lett., 274, 214-220.
Hynek, B. M., M. Beach, and M. R. T. Hoke (2010), Updated global map of martian valley
networks and implications for climate and hydrological processes, J. Geophys. Res.,
doi:10.1029/2009JE003548, in press.
Irwin, R. P., and A. D. Howard (2002), Drainage basin evolution in Noachian Terra Cimmeria,
Mars, J. Geophys. Res., 107, 5056, doi:5010.1029/2001JE001818.
Irwin, R. P., A. D. Howard, R. A. Craddock, and J. M. Moore (2005), An intense terminal epoch
of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake
development, J. Geophys. Res., 110, E12S15, doi:10.1029/2005JE002460.
Jakosky, B. M., and J. H. Jones (1997), The history of Martian volatiles, Rev. Geophys., 35, 116.
Johnson, S. S., M. A. Mischna, T. L. Grove, and M. T. Zuber (2008), Sulfur-induced greenhouse
warming
on
early
Mars,
J.
Geophys.
Res.,
113,
E08005,
doi:08010.01029/02007JE002962.
Lamb, M. P., W. E. Dietrich, S. M. Aciego, D. J. DePaolo, and M. Manga (2008), Formation of
Box Canyon, Idaho, by MegaFlood: Implications for seepage erosion on Earth and Mars,
Science, 320, 1067-1070.
Laskar, J., A. C. M. Correia, M. Gastineau, F. Joutel, B. Levrard, and P. Robutel (2004), Long
term evolution and chaotic diffusion of the insolation quantities of Mars, Icarus, 170,
343-364.
Levrard, B., F. Forget, F. Montmessin, and J. Laskar (2007), Recent formation and evolution of
northern Martian polar layered deposits as inferred from a Global Climate Model, J.
Geophys. Res., 112, E06012, doi:06010.01029/02006JE002772.
Lewis, K. W., O. Aharonson, J. P. Grotzinger, R. L. Kirk, A. S. McEwen, and T.-A. Suer (2008),
Quasi-periodic bedding in the sedimentary rock record of Mars, Science, 322, 1532-1535.
Lewis, K. W., O. Aharonson, J. P. Grotzinger, A. S. McEwen, and R. L. Kirk (2010), Global
significance of cyclic sedimentary deposits on Mars, Lun. Plan. Sci., 41, abstract 2648.
Lillis, R. J., H. V. Frey, M. Manga, D. L. Mitchell, R. P. Lin, M. H. Acuna, and S. W. Bougher
(2008), An improved crustal magnetic field map of Mars from electron reflectometry:
Highland volcano magmatic history and the end of the martian dynamo, Icarus, 194, 575596.
Lunine, J. I., J. Chambers, A. Morbidelli, and L. A. Leshin (2003), The origin of water on Mars,
Icarus, 165, 1-8.
Malin, M. C., and K. S. Edgett (2000), Sedimentary rocks of early Mars, Science, 290, 19271936.
McLennan, S. M., J. F. Bell, W. Calvin, P. R. Christensen, B. C. Clark, P. A. de Souza, J.
Farmer, W. H. Farrand, D. A. Fike, R. Gellert, A. Ghosh, T. D. Glotch, J. P. Grotzinger,
B. Hahn, K. E. Herkenhoff, J. A. Hurowitz, J. R. Johnson, S. S. Johnson, B. L. Jolliff, G.
Klingenhofer, A. H. Knoll, Z. Learner, M. C. Malin, H. Y. McSween, J. Pocock, S. W.
Ruff, L. Soderblom, S. W. Squyres, N. J. Tosca, W. A. Watters, M. B. Wyatt, and A. Yen
(2005), Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani
Planum, Mars, Earth Planet. Sci. Lett., 240, 95-121.
59
Mellon, M. T., and B. M. Jakosky (1995), The distribution and behavior of Martian ground ice
during past and present epochs, J. Geophys. Res., 100(E6), 11,781-711,799.
Melosh, H. J., and A. M. Vickery (1989), Impact erosion of the primordial atmosphere of Mars,
Nature, 338, 487-489.
Mohit, P. S., and J. Arkani-Hamed (2004), Impact demagnetization of the martian crust, Icarus,
168(2), 305-317.
Moore, J. M., and D. E. Wilhelms (2001), Hellas as a possible site of ancient ice-covered lakes
on Mars, Icarus, 154, 258-276.
Murchie, S. L., L. Roach, F. Seelos, R. E. Milliken, J. Mustard, R. Arvidson, S. M. Wiseman, K.
A. Lichtenberg, J. C. Andrews-Hanna, J. Bishop, J.-P. Bibring, M. Parente, and R. V.
Morris (2009), Evidence for the origin of layered deposits in Candor Chasma, Mars, from
mineral
composition
and
hydrologic
modeling,
J.
Geophys.
Res.,
doi:10.1029/2009JE003343, in press.
Mustard, J. F., S. L. Murchie, B. L. Ehlmann, R. E. Milliken, J.-P. Bibring, F. Poulet, L. Roach,
and F. Seelos (2008a), Regional geology and stratigraphy of the Nili Fossae-Syrtis-Isidis
region: New insights from CRISM and MRO data, Lun. Plan. Sci., XXXIX, abstract 1701.
Mustard, J. F., S. L. Murchie, S. M. Pelkey, B. L. Ehlmann, R. E. Milliken, J. A. Grant, J.-P.
Bibring, F. Poulet, J. Bishop, E. Z. Noe Dobrea, L. Roach, F. Seelos, R. E. Arvidson, S.
M. Wiseman, R. Green, C. Hash, D. Humm, E. R. Malaret, J. A. McGovern, K. Seelos,
T. Clancy, R. Clark, D. Des Marais, N. Izenberg, A. Knudson, Y. Langevin, T. Z. Martin,
P. C. McGuire, R. V. Morris, M. S. Robinson, T. L. Roush, M. Smith, G. A. Swayze, H.
Taylor, T. N. Titus, and M. Wolff (2008b), Hydrated silicate minerals on Mars observed
by the Mars Reconnaissance Orbiter CRISM instrument, Nature, 454, 305-309.
Mutch, T. A., R. E. Arvidson, and J. W. Head (1976), The geology of Mars, Princeton University
Press, Princeton, NJ.
Oehler, D. Z., and C. C. Allen (2010), Evidence for pervasive mud volcanism in Acidalia
Planitia, Mars, Icarus, 208, 636-657.
Phillips, R. J., M. T. Zuber, S. C. Solomon, M. P. Golombek, B. M. Jakosky, W. B. Banerdt, D.
E. Smith, R. Williams, B. Hynek, O. Aharonson, and S. A. I. Hauck (2001), Ancient
geodynamics and global-scale hydrology on Mars, Science, 291, 2587-2591.
Phillips, R. J., M. T. Zuber, S. E. Smrekar, M. T. Mellon, J. W. Head, K. L. Tanaka, N. E.
Putzig, S. M. Milkovich, B. A. Campbell, J. J. Plaut, A. Safaeinili, R. Seu, D. Biccari, L.
M. Carter, G. Picardi, R. Orosei, P. S. Mohit, E. Heggy, R. W. Zurek, A. F. Egan, E.
Giacomoni, M. Cutigni, E. Pettinelli, J. W. Holt, C. J. Leuschen, and L. Marinangeli
(2008), Mars north polar deposits: Stratigraphy, age, and geodynamical response,
Science, 320, 1182-1185.
Plaut, J. J., G. Picardi, A. Safaeinili, A. B. Ivanov, S. M. Milkovich, A. Cicchetti, W. Kofman, J.
Mouginot, W. M. Ferrell, R. J. Phillips, S. M. Clifford, A. Frigeri, R. Orosei, C.
Frederico, I. P. Williams, D. A. Gurnett, E. Nielsen, T. Hagfors, E. Heggy, E. R. Stofan,
D. Plettemeier, T. R. Watters, C. J. Leuschen, and P. Edenhofer (2007), Subsurface radar
sounding of the south polar layered deposits of Mars, Science, 316, 92-95.
Poulet, F., J.-P. Bibring, J. F. Mustard, A. Gendrin, N. Mangold, Y. Langevin, R. E. Arvidson, B.
Gondet, and C. Gomez (2005), Phyllosilicates on Mars and implications for early martian
climate, Nature, 438(7068), 623-627.
60
Richardson, M. I., A. D. Toigo, and C. E. Newman (2007), PlanetWRF: A general purpose, local
to global numerical model for planetary atmospheric and climate dynamics, J. Geophys.
Res., 112, E09001, doi:09010.01029/02006JE002825.
Roach, L. H., J. F. Mustard, M. D. Lane, J. L. Bishop, and S. L. Murchie (2010a), Diagenetic
haematite and sulfate assemblages in Valles Marineris, Icarus, 207, 659-674.
Roach, L. H., J. F. Mustard, G. A. Swayze, R. E. Milliken, J. L. Bishop, S. L. Murchie, and K. A.
Lichtenberg (2010b), Hydrated mineral stratigraphy of Ius Chasma, Valles Marineris,
Icarus, 206, 253-268.
Soto, A., M. I. Richardson, and C. E. Newman (2010), Global Constraints on Rainfall on Ancient
Mars: Oceans, Lakes, and Valley Networks, Lun. Plan. Sci., 41, abstract 2397.
Squyres, S. W., and A. H. Knoll (2005), Sedimentary rocks at Meridiani Planum: Origin,
diagenesis, and implications for life on Mars, Earth Planet. Sci. Lett., 240, 1-10.
Squyres, S. W., A. H. Knoll, R. E. Arvidson, B. C. Clark, J. P. Grotzinger, B. L. Jolliff, S. M.
McLennan, N. J. Tosca, J. F. Bell, W. M. Calvin, W. H. Farrand, T. D. Glotch, M. P.
Golombek, K. E. Herkenhoff, J. R. Johnson, G. Klingelhofer, H. Y. McSween, and A. S.
Yen (2006), Two years at Meridiani Planum: Results from the Opportunity rover,
Science, 313, 1403-1407.
Stepinski, T. F., and M. L. Collier (2004), Extraction of Martian valley networks from digital
topography, J. Geophys. Res., 109(E11), E1105, doi:1110.1029/2004JE002269.
Stepinski, T. F., and A. P. Stepinski (2005), Morphology of drainage basins as an indicator of
climate on early Mars, J. Geophys. Res., 110, E12S12, doi:10.1029/2005JE002448.
Tosca, N. J., S. M. McLennan, B. C. Clark, J. P. Grotzinger, J. A. Hurowitz, A. H. Knoll, C.
Schroder, and S. W. Squyres (2005), Geochemical modeling of the evaporation processes
on Mars: Insight from the sedimentary record at Meridiani Planum, Earth Planet. Sci.
Lett., 240, 122-148.
Williams, R. M. E., and R. J. Phillips (2001), Morphometric measurements of martian valley
networks from Mars Orbiter Laser Altimeter (MOLA) data, J. Geophys. Res., 106(E10),
23737-23751.
Wiseman, S. M., R. E. Arvidson, J. C. Andrews-Hanna, R. N. Clark, N. Lanza, D. Des Marais,
G. A. Marzo, R. V. Morris, S. L. Murchie, H. E. Newsom, E. Z. Noe Dobrea, A. M.
Ollila, F. Poulet, T. L. Roush, F. P. Seelos, and G. A. Swayze (2008), Phyllosilicate and
sulfate-hematite deposits within Miyamoto crater in southern Sinus Meridiani, Geophys.
Res. Lett., 35, L19204, doi:19210/11029/12008GL035363.
Wiseman, S. M., R. E. Arvidson, R. V. Morris, F. Poulet, J. C. Andrews-Hanna, J. L. Bishop, S.
L. Murchie, F. P. Seelos, D. Des Marais, and J. L. Griffes (2010), Spectral and
stratigraphic mapping of hydrated sulfate and phyllosilicate-bearing deposits in northern
Sinus Meridiani, Mars, J. Geophys. Res., 115, E00D18, doi:10.1029/2009JE003354.
Wray, J. J., R. E. Milliken, G. A. Swayze, C. M. Dundas, J. L. Bishop, S. L. Murchie, F. P.
Seelos, and S. W. Squyres (2009), Colombus crater and other possible paleolakes in
Terra Sirenum, Mars, Lun. Plan. Sci., 40, abstract 1896.
Yung, Y. L., J.-S. Wen, J. P. Pinto, M. Allen, K. K. Pierce, and S. Paulsen (1988), HDO in the
Martian atmosphere: Implications for the abundance of crustal water, Icarus, 76, 146159.
Zabrusky, K. J., and J. C. Andrews-Hanna (2010), Reconstructing the original volume and extent
of the sedimentary deposits of Meridiani Planum and Arabia Terra, Lun. Plan. Sci., 41,
abstract 2529.
61
Zuber, M. T., R. J. Phillips, J. C. Andrews-Hanna, S. W. Asmar, A. S. Konopliv, F. G. Lemoine,
J. J. Plaut, D. E. Smith, and S. E. Smrekar (2007), Density of Mars' south polar layered
deposits, Science, 317, 1718-1719.
62