Revised Table of Goals, Objectives and Investigations (12 February 2013)
In outline form, the Goals are the top level roman numerals (I, II, & III). The three goals are all of equal
priority. Within each Goal, Objectives are listed in priority order (A, B, C, & D). Within each Objective,
Investigations are also listed in priority order (1, 2, 3, etc.).
I. Origin and Evolution
A. How did Venus form and initially evolve?
1. Characterize elemental composition and isotopic ratios of noble gases in the Venus
atmosphere, especially Xe, Kr, 40Ar, 36Ar, Ne, 4He, 3He, to constrain origin and sources and
sinks driving evolution of the atmosphere.
2. Determine isotopic ratios of H/D, 15N/14N, 17O/16O, 18O/16O, 34S/32S and 13C/12C in the
atmosphere to constrain paleochemical disequilibria, atmospheric loss rates, the history of
water, and paleobiosignatures.
B. Were interior dynamics different in the past?
1. Combine geophysical (gravity, seismology, etc) and surface observations to characterize the
structure, dynamics, and history of the interior of Venus, including possible evolution from
plate tectonics to stagnant-lid tectonics.
2. Through high-resolution imaging and topography, characterize the nature of surface
deformation over the planet's history, particularly with respect to evidence for significant
horizontal surface movement, in order to understand past coupling of the surface to interior
convective flow.
3. Characterize radiogenic 4He, 40Ar & Xe isotopic mixing ratios generated through radioactive
decay to determine the mean rate of interior outgassing over Venus’s history.
C. Was the Venus surface environment different in the past?
1. At the surface, identify major and minor element (including H) chemical compositions,
petrology, and minerals in which those elements are sited (for example, hydrous minerals to
place constraints on past habitable environments).
2. Characterize gases trapped in rocks for evidence of past atmospheric conditions.
II. Venus as a Terrestrial Planet
A. What is the chemistry and mineralogy of the crust and what does it tell us about the
history of Venus?
1. Determine elemental composition and mineralogy of surface samples at key geologic sites,
particularly in terrains that have never been sampled, such as the highlands (tesserae), in
order to address questions about atmosphere-surface-interior interactions.
2. Determine compositional information for rocks at regional scales using remote sensing to
gain a global scale picture of geochemical processes.
3. Assess the petrography (shapes, sizes, & mineral grain relationships) & petrology (formation
characteristics) of surface rocks in locations that are key to understanding magmatic,
tectonic, and weathering processes.
4. Evaluate the characteristics of weathering rinds, and characterize the chemical compositions
of near-surface rocks beneath any weathering rind in order to constrain rates of resurfacing
and past weathering processes, and the composition of un-weathered rocks.
5. Determine absolute ages for rocks at locations that are key to providing constraints on
global resurfacing rates.
B. What is the nature and rate of current and past volcanic and tectonic activity?
1. Characterize stratigraphy of surface units through detailed imaging and topography to learn
the overall sequence of events in Venusian surface history.
2. Assess geomorphological, geochemical, and geophysical evidence of evolution in volcanic
styles in order to evaluate surface-interior evolution scenarios such as catastrophic
resurfacing.
3. Characterize active volcanic processes such as ground deformation, flow emplacement, or
thermal signatures to constrain the current rate of resurfacing.
4. Characterize active tectonic processes observed through, for example, image analysis,
measurements of ground deformation, and seismic activity to constrain the current level of
tectonic activity.
5. Characterize the materials emitted from volcanoes, including lava and gases, in terms of
chemical compositions, chemical species, and mass flux over time in order to evaluate the
nature of recent and current volcanism.
C. What is the planet’s current interior like?
1. Determine the structure of the crust, as it varies both spatially and with depth, through high
resolution measurements of topography and gravity in order to constrain lithospheric
structure and processes.
2. Measure heat flow and surface temperature to constrain the thermal structure of the
interior.
3. Characterize subsurface layering and geologic contacts to depths up to several km to
enhance understanding of crustal processes.
4. Use measurements of seismic layering and of rotational dynamics, such as the moment of
inertia, to determine the structure of the interior, including the crust, lithosphere, mantle,
and core, through.
5. Characterize the magnetic field below the ionosphere and magnetic signatures of rocks in
multiple locations to constrain the evolutionary history of the core.
D. How does Venus’s atmosphere work?
1. Characterize the sulfur cycle through measurements of abundances within the Venus clouds
of relevant gaseous and liquid/solid aerosol components such as SO2, H2O, OCS, CO, and
sulfuric acid aerosols (H2SO4).
2. Characterize Venus’s global superrotation and meridional circulation through
measurements of:
a) global-horizontal winds over the full range of longitudes for mid and high latitude
bands at a constant altitude to determine the role of semi-diurnal and diurnal tides
and to constrain meridional Hadley-like cells,
3.
4.
5.
6.
7.
b) energy deposition in the cloud layers, including the microphysical characteristics
(size, shape, albedo, phase function) of the mysterious UV absorber and H2SO4 cloud
particles, to determine the role of cloud heating in powering super-rotation, and
c) vertical motions in the clouds, to constrain the roles of high-altitude gravity waves
and convection in the vertical transport of thermal and mass fluxes.
Characterize local dynamical meteorology in the middle cloud layer through the
measurement of vertical winds and temperatures associated with convection, turbulence,
and concurrent measurements of cloud particle densities , sizes, and the local abundances
of their parent vapors, all cloud-formation processes (including both day and night
conditions) to understand the coupled dynamical/chemical processes involved in the
meteorology of sulfur-driven, CO2-based terrestrial planet.
Determine the mechanisms behind atmospheric loss to space, the current rate, and its
variability with solar activity to provide important constraints on the on-going evolution of
Venus’s atmosphere.
Investigate the chemical mechanisms for stability of the atmosphere against photochemical
destruction of CO2 to constrain the evolution of the dominant material in Venus’s
atmosphere.
Measure the frequencies and strengths of lightning and determine the role of lightning in
generating chemically-active species (e.g., NOx) that could uniquely influence Venus’s
environment.
Search for and characterize biogenic elements, especially in the clouds, to provide insight
into the prevalence of biologically-important chemistry in non-Earthlike environments.
III. Habitability and Climate Evolution
A. What is the Role of the Venus Greenhouse in producing the planet’s current climate?
1. Determine the radiative balance as a function of latitude, and longitude, including
measurements of (a) deposition of solar energy over altitude, especially within the clouds
(b) outgoing thermal flux, to understand the fundamental driving “engine” of the
atmosphere,
2. Determine microphysical properties and particle densities of aerosols, including their size,
distribution, shapes, composition, and UV, visible, and IR spectral character to elucidate the
role of aerosols in determining Venus’s climate.
3. Determine the vertical-atmospheric temperature profile and characterize variability to
refine our understanding of Venus’s thermal climate.
B. Did Venus ever have surface water?
1. Determine the isotopic ratios of H/D, 15N/14N, 17O/16O, 18O/16O, 34S/32S 13C/12C in solid
samples to place constraints on past habitable environments (including possible oceans).
2. Identify and characterize any areas that reflect formation in a geological or climatological
environment significantly different from present day in order to evaluate whether (and
when) geologic processes consistent with habitable environments existed.
C. Characterize how the interior, surface, and atmosphere interact
1. Determine the abundances and altitude profiles of reactive atmospheric species (OCS, H2S,
SO2, SO3, H2SO4, Sn, HCl, HF, SO3, ClO2 and Cl2), greenhouse gases, H2O, and other
condensables, in order to characterize sources of chemical disequilibrium in the
atmosphere.
2. Determine rates of gas exchange between the interior, surface and atmosphere to place
constraints on the coupling of chemical processes between the surface and near-surface
atmosphere.