Chapter 10: Mars
A Near Miss
Life?
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Orbital Properties
Physical Properties
Seasons
Surface Features
Atmosphere
Satellites
Comparison to
Earth and Venus
for
Objectives
• After completing this chapter, you should be able to:
• compare the general physical properties of Mars, Earth, Venus,
Mercury, and the Moon.
• compare the orbital and rotational properties of Mars, Earth,
Venus Mercury, and the Moon.
• describe the atmosphere, hydrosphere, lithosphere,
magnetosphere, and biosphere of Mars and
• compare to the terrestrial planets and explain their differences.
• describe Mars' cycle of visibility as seen from the Earth.
• describe the physical properties and origin of the Martian
moons.
• describe the "geologic" history of Mars and compare it to the
other terrestrial planets.
Planetary Configurations
• In their orbital cycles, planets assume various
configurations relative to the Sun-Earth line.
• For a planet farther from the Sun than Earth:
–opposition - planet is closest to Earth and
appears to be opposite the Sun
(from Earth).
–conjunction - planet is farthest from the Earth
and the Sun lies between the
planet and Earth.
–quadrature - planet is 90o from the Sun-Earth
line.
Superior Planet
Configurations
Earth-Sun line
Conjunction
Quadrature
Opposition
Mars from Earth
• Mars appears largest and brightest when it is at
opposition.
• If also at perihelion, Mars
– is within 0.38 AU (56 million miles) of Earth,
– has an angular size of 25”,
– has surface features as small as 100 km across that can be
resolved by Earth-based telescopes (about the same size as
objects on the Moon resolved by unaided eye).
– Will occur again in August 2003.
• Mars appears less bright than Venus.
– Twice as far from the Sun
– surface area about 30% that of Venus
– less reflective surface - only 15% of incident light reflected
Distance from Mars to Earth
• Mars becomes easily visible about once every two years
(780 days OR the period between oppositions), when it is
– closest to the Earth,
– visible all night long, and
– highest in the sky at midnight.
• At maximum brightness, it is the second brightest planet.
Earth-based Studies of Mars
• First telescopic observations by Galileo.
• Small angular size of Mars, Earth’s atmospheric
turbulence limit observations
– show daily changes in surface due to rotation
– seasonal changes in colors of regions
– length of day
– tilt of rotation axis
• 19th century observations by Schiaparelli interpreted
surface as criss-crossed by straight lines, called canali.
• U.S. astronomer Percival Lowell also observed the
features in 1896; others did not.
• Debate continued over half a century.
Mars in Two Views
Early Exploration from Space
• In 1965, Mariner 4 passed near Mars and sent
back 22 photographs of the surface.
First picture of Mars
from Mariner 4
First picture of craters
on surface of Mars
Early Exploration from Space
• In 1971, Mariner 9 was the first spacecraft to
orbit another planet and sent back a series of
photographs showing volcanoes (Olympus Mons),
valleys (Valles Marineris), craters, and channels.
Early Exploration from Space
• The Viking missions each had 2 spacecraft,
orbiter and lander, to obtain high resolution
images of the surface, examine the surface
geology, and search for evidence of life.
Recent Missions to Mars
• Pathfinder w/ Sojourner explored the Martian surface in 1997.
• Mars Global Surveyor: arrived in Martian orbit Sept. 12, 1997.
• Mars Polar Explorer: Lost contact December, 1999
Mars Global Surveyor
Mars Global Surveyor: arrived in Martian orbit Sept. 12, 1997.
Chasm in
Valles Marineris
Possible
evidence of
ponding in
Martian crater
Plateau in Valles Marineres
Current Mission: Mars Odyssey
http://www.jpl.nasa.gov/odyssey/
•
Mars Odyssey carries three scientific instruments
designed to tell us what the Martian surface is made
of and about its radiation environment:
– a thermal-emission imaging system,
– a gamma ray spectrometer and
– a Martian radiation environment experiment.
•
Odyssey arrived at Mars on October 24, 2001, when it fired its main engine
and was captured into Mars' orbit.
Odyssey
Current Mission: Mars Odyssey
Current Mission: Mars Odyssey
http://www.jpl.nasa.gov/odyssey/
This thermal infrared image
was the first acquired by Mars
Odyssey's thermal emission
imaging system on October 30,
2001. It is late spring in the
Martian southern hemisphere.
The extremely cold, circular
feature shown in blue is the
Martian south polar carbon
dioxide ice cap at a temperature
of about -120 °C (-184 ° F).
Clouds of cooler air blowing off
the cap can be seen in orange
extending across the image to
the left of the cap. The thin blue
crescent along the upper limb of
the planet is the Martian
atmosphere. (NASA/JPL)
Mars Statistics
•Satellites: 2
•Diameter: 6,785 km (0.52x Earth)
•Mass: 0.11 x Earth
•Density: 3.9 g/cm3 (Moon=3.3,Earth=5.5)
•Surface Gravity: 0.38 x Earth
•Escape Speed: 5.0 km/sec
•Length of Solar Day: 24 hrs 37 min
•Length of year: 687 Earth days
•Orbital semi-major axis: 1.52 AU
•Tilt of Axis: 23o59”
•Orbital eccentricity: 0.093
•Minimum Distance from Sun: 205 million km (128 million miles)
•Maximum Distance from Sun: 249 million km (155 million miles)
•Temperature: 150K to 310K ( -116oF to 34oF), 218K average
•Surface magnetic field: 1/800 X Earth
Seasons on Mars
•Mars’ axial tilt only slightly greater than Earth’s.
– expect seasons similar to Earth.
•Mars’ orbital eccentricity greater than Earth’s.
– S-hemisphere closest to Sun during summer,
and farthest from the Sun during winter.
•Summers warmer in S-hemisphere
than N-hemisphere.
•Winters colder in S-hemisphere than N-hemisphere.
•Prediction for polar ice caps and
variations with season?
Martian Sunset
Picture taken by Mars Pathfinder mission.
The color of the Sun is not correct since it is overexposed
(should appear white or bluish-white).
Atmospheric Composition of Mars
• Composition
– 95.3% carbon dioxide
– 2.7% nitrogen
– 1.6 % argon
– 0.13 % oxygen
– 0.07% carbon monoxide
– 0.03 % water vapor
• Atmospheric pressure at the surface of Mars is ~
1/100 x Earth’s.
– may vary by 30% throughout Mars year because of
variations in solar heating.
• No recorded lightning or thunder.
Atmosphere of Mars
•Troposphere where convection
and "weather" occur.
– Two types clouds:
• water vapor w/ carbon dioxide;
– white
– appear in low-lying areas in morning
– near poles in late summer/early fall
• dust
– yellowish
– high speed surface winds (>100mph)
•At noon in the summertime,
surface temperatures may reach
>300 K.
•At night,
– temperatures drop up to 100 K,
– convection ceases, and
– troposphere vanishes.
Atmosphere: Pressure and Temperature
• Atmospheric pressure changes seasonally as carbon
dioxide freezes and then evaporates from polar caps.
• During southern hemisphere winters,
the global air pressure drops by 30%.
• Seasonal changes are also affected by Mars' distance
from the Sun, and are also the cause of planet-wide
dust storms that can obscure the planet's surface.
• Diurnal temperature changes are quite extreme
ranging from -225 F at night to 63 F during the day.
– The greatest extremes occur in the southern hemisphere.
– Occasionally carbon dioxide and water vapor clouds form
because of the low temperature in the atmosphere.
– Also frost can form on the ground.
Martian Dust Storms
Martian
Dust Devil
animation file:///H|/phys1050-fall2001/pictures/dustdevil.gif
Comparing Terrestrial
Atmospheres
PLANET
COMPOSITION
PRESSURE
Earth
Nitrogen/Oxygen
1 atmosphere
Venus
Carbon dioxide
100 atmosphere
Mars
Carbon dioxide
0.01 atmosphere
Goldilocks
and the
3 Planets:
A story about
the
Greenhouse
Effect
Atmospheric History
1. Primary and secondary atmospheres similar to
Earth and Venus.
2. Moderate greenhouse effect warms surface and
allows liquid water to form.
3. Water dissolves carbon dioxide to form carbonate
rocks.
4. Reduced carbon dioxide content diminishes
greenhouse effect, so planet cools.
5. The surface atmospheric pressure decreases so
that most of the liquid water is frozen.
6. Steps #4 & 5 propagate a runaway ice age effect.
Assuming no weathering, no life, and no gases escaping,
atmospheres of the terrestrial planets would be:
VENUS
EARTH
MARS
Nitrogen
3.4%
1.9%
1.7%
Oxygen
Trace
Trace
Trace
Argon
40 ppm
190 ppm
850 ppm
Carbon dioxide
96.5%
98%
98%
Pressure
0.88 atm
0.7 atm
0.02 atm
Water depth
9m
3 km
30 m
Martian Hydrosphere
• Liquid water is not expected on surface of Mars today.
• The pressure and temperature combination is too low
for liquid water to be stable, except possibly at the
bottom of a deep canyon.
– Only Earth in the inner Solar System has
large amounts of liquid water.
• Very little water vapor in the Martian atmosphere.
– Less than Earth or Venus, but the relative humidity is 100%!
• A comparison of atmospheric and ground water shows:
PLANET
ATMOSPHERE
GROUND
Mars
0.01 mm
10-160 m
Venus
30 mm
9m
Earth
100 mm
3000 m
Evidence for Recent Water at Surface
Images from Surveyor suggest geologically recent seeps of
water to the Martian surface in gully landforms observed
from latitudes of 300 - 700 in both hemispheres.
Martian Climate Changes
• Mars is currently locked in a global ice age.
It may not have always been that way in the past.
• Changes in the tilt of its axis, orbital eccentricity,
and/or precession of its rotation axis caused by
the gravitational influence Jupiter could have
greatly altered the Martian climate.
• It may have been possible for liquid water to
exist on the surface or Mars in the past.
Polar Regions of Mars
• Polar ice caps composed of
– water ice
– carbon dioxide ice.
• In summer, dry ice in N-cap
sublimates and leaves water
ice remnant.
• S-cap retains some dry ice
year round.
• Layering observed in polar
deposits implies periodic
sedimentation from longterm, repetitive climate
changes.
Mariner 9 images
N-pole cap
S-pole cap
Evidence of Water on Mars?
Runoff channels: resemble Earth’s river systems, ~4 billion years old
Water Erosion?
Outflow channel: relic of catastrophic flooding ~3 billion years ago.
Run-off Channels
Observations suggest that this water may have melted in the past causing huge floods.
Other evidence points to runoff channels that might have formed under rainy conditions.
(Photo from MOLA, Mars Global Surveyor)
Evidence of Water in the Past
Sedimentary rock layers like these in
Mars's Holden Crater suggest that the Red
Planet was once home to ancient lakes.
Martian gullies in Newton Crater. Scientists
hypothesize that liquid water burst out from
underground, eroded the gullies, and pooled at the
bottom of this crater as it froze and evaporated.
New Information from
Mars Global Surveyor
•Wide-spread presence of olivine at surface suggests drier and colder
throughout history than previously theorized.
•green (yellow/green) - sulfates
red - sulfate-free
blue - olivine and pyroxenes (both volcanic)
magenta - coarse-grained hematite
Seismic Activity on Mars
• Each Viking lander carried a
seismometer;
only one worked.
• Showed that Mars does have some seismic
activity, but that the activity per unit area on
Mars is less than on Earth.
• Mars quakes that were recorded lasted about a
minute.
– Earthquakes last seconds
– moonquakes last hours
• Internal structure of Mars more similar to Earth
than Moon.
The Surface of Mars
• Mars Viking landers answered
“why is Mars red?”
• Viking soil analysis showed surface to consist of
– mostly silicate rocks
– large fraction (20%) as iron oxide
• Soil is magnetic.
• High surface abundance of iron combined with
the overall density implies that Mars should not
have much of an iron core. That is, Mars should
show little differentiation.
Mars: Internal Structure
• No direct measurements to
constrain models of interior.
• Average density and volcanic
history imply some interior
melting and differentiation.
– thin crust (65-80 km)
– rocky mantle more dense
than Earth
– small iron-rich core,
possibly w/ sulfur
• Lack of detectable magnetic field
implies core is non-metallic
and/or non-liquid.
• No widespread geological activity
in last ~2 billion years.
Martian Interior and Tectonics
• There are no seismic data from Mars,
because this equipment failed on one of the
Viking landers.
• Other indirect evidence suggests that Mars
probably has no large iron core, and that
the interior is not well differentiated.
• The mantle must have been hot to cause
volcanoes and rift valleys, but the crust may
be too thick to allow plate tectonics to begin.
• The planet probably froze solid before plate
tectonics could begin.
Plate Tectonics
• The mantle must have been hot to cause
volcanoes and rift valleys, but the crust
may be too thick to allow plate tectonics
to begin.
• The planet probably froze solid before
plate tectonics could begin.
Crustal Thickness
North
Red - thin
Blue - thick
Crustal thickness may be inferred from gravity observations
made by Mars Global Surveyor.
Martian Magnetosphere
• No magnetic field has been detected, so
the solar wind can interact directly with
the Martian atmosphere.
• No magnetic field suggests Mars has no
or a very small liquid metallic core.
Martian Lithosphere
Viking 1 view from surface of Mars
Surface
Features:
A view
from
HST
• Highlands - 60%
Terrains on Mars
–ancient
–heavily cratered terrain
–southern hemisphere
• Northern Lowlands - 20%
–younger, lightly cratered
–resemble lunar maria
–average elevation 4 km below highlands
–dune fields, rift valleys, dry riverbeds, water flow patterns
• Volcanic Highlands - 20%
–Tharsis volcanic province
–immense bulge the size of North America
–volcanic plains, 10 km above surroundings
–crowned by 4 volcanoes that rise another 15 km
–few impact craters
The Surface of Mars
• Mars Global Surveyor has been recording thermal
emission spectra from the surface of Mars.
• Analysis of the data suggests
– low albedo regions composed of
• volcanic basalts in the S-hemisphere
• andesitic volcanics in N-hemisphere
– high albedo regions show anomalous spectra
consistent with atmospheric dust
Maps from Mars Global Surveyor:
Hellas region
Craters on Mars Highlands
•
This mosaic of Viking images shows a portion of a cratered highland
region on Mars (U.S. Geological Survey; data from NASA)
Craters on Mars
Copernicus: typical impact crater
on the Moon, ejecta appears as
dry, powdery material
Yuty: impact crater on Mars,
ejecta appears liquid,
“splosh” crater
Maps from Mars Global Surveyor:
Utopia region
Northern Lowlands
• The northern hemisphere lowlands have a
number of very interesting landscapes.
• Large dune fields have been detected from
orbiting spacecraft.
– The largest of these fields is about the size of
Colorado or Nebraska with combined groups the
size of Texas.
– The amount of sand in these dunes is comparable to
the volume of Mars' smallest moon (Deimos).
Maps from Mars Global Surveyor:
Tharsis region
Olympus Mons
Largest known volcano in our solar system,
shield volcano with 3 x elevation of Mt. Everest on Earth
Olympus Mons -Perspective
Base:
700 km diameter
Caldera: 80 km across
Height: 25 km higher than surrounding plains
and surrounded by a 6 km high cliff
Alba Patera
Two views of Alba Patera with topography draped over a Viking image
mosaic. The vertical exaggeration is 10:1. (Credit: MOLA Science Team)
Arisa Mons
Two views of Arsia Mons, the southern most of the Tharsis montes, shown as
topography draped over a Viking image mosaic. MOLA topography clearly shows the
caldera structure and the flank massive breakout that produced a major side lobe.
The vertical exaggeration is 10:1. (Credit: MOLA Science Team)
Valles
Marineris
• Discovered
by Mariner 9
• On Earth,
would
stretch from
Los Angeles
to New York
Valles Marineris: The Grand Canyon of Mars
Cause: tectonic fracture of crust
Length: ~4000 km
Depth: to 7 km
Width: to 120 km
Flow from Highlands to Lowland Plain
Ancient riverbeds on Mars. At the lower center are several river channels showing
northward flow (upward in the figure) from the edge of a highland scarp to a lowland
plains region called Amazonis Planitia. (U.S. Geological Survey; data from NASA)
Martian Biosphere
• MARTIAN SCIENCE FICTION
– Percival Lowell
– War of the Worlds
• THE VIKING LANDER RESULTS
– All data gathering can be explained by non-biological
processes.
– No organic compounds found.
– Soil appears to have the properties of peroxide (antiseptic!).
– It is possible that life formed but is now extinct.
• MARTIAN METEORITES
– Martian meteorites appear to have structures
that resemble microfossils.
– No definitive conclusion has been reached yet.
NASA’s Plan to Look for Life on Mars
• Options for Search
– Look for life
• fossils
• extant organisms
– Look for evidence of life
• chemical processes
• biological/chemical signatures
– Search for environments which might have
sustained life
• ancient groundwater environments
• surface water environments
• modern groundwater environments
Life Sustaining Environments
• Ancient groundwater environments
– possible warm groundwater circulation in highlands
– deposits exposed at surface in ejecta from recent
impact craters
• Surface water environments
– liquid water flowed and pooled in low-lying regions
– solar heating provided energy for biology
– evidence in water lain sediments in valley systems
and basins in highlands
• Modern groundwater environments
– life survived from early epoch in places beneath the
surface where liquid water is present today.
Viking 1&2
Experiments
A Search for
Earth-like Life on Mars
Four basic experiments.
Samples were isolated in chambers and exposed to a variety of gases,
radioactive isotopes and nutrients to look for evidence of
respiration by living animals,
absorption of nutrients offered to any organisms present, and
an exchange of gases between the soil and its surroundings.
Another sample was pulverized and analyzed for
organic (carbon-bearing) materials.
These experiments were built around the hypothesis that if there
were life on Mars it would have a similar metabolism to life on
Earth, and it would have a similar biochemistry based on the same
organic compounds important to life on Earth.
Results of the Viking Expeditions
The results of these experiments were complex. The first
three gave positive results, but the complete absence of any organic
compounds in the Martian soil according to the mass spectrometer
experiment suggests that the positive results for the first three were
not evidence for life, but rather evidence for a complex inorganic
chemistry in the Martian soil. Thus, the Viking verdict was that
there was no evidence for present or past life on Mars.
Geologic History
1.
2.
3.
4.
5.
6.
7.
8.
9.
Condensation from the solar nebula.
Accretion of planetesimals into the planet.
Short period of completely molten state.
Partial differentiation.
Formation of thick rigid crust.
Impact cratering.
Volcanic and tectonic activity, but no plate tectonics.
Interior cools.
Relatively inactive today,
but some geologic processes exist.
Moons of Mars
Phobos
Deimos
27 km diameter,
Stickney crater,
7.5 hour orbital period
15 km diameter,
smoother, less cratered,
30 hour orbital period
Irregular shape, pitted with craters, density = 2 g/cm3,
circular orbits in equatorial plane.
Martian Moons
• Phobos and Deimos are both extremely small
(about 20 miles across).
• They may be captured asteroids, because Mars
lies on the inner edge of the asteroid belt.
• They appear to be rich in carbon compounds
and show some evidence of volcanic vents.
• Phobos revolves around Mars in just 7.5 hours,
so it rises in the west and sets in the east.
• Both moons exhibit synchronous rotation with
the same side of the moon always facing Mars.
• The motions of these moons were used to
determine the mass of Mars in 1877.
Spheres: Earth, Venus, Mercury,
Mars and the Moon
REALM
EARTH
VENUS
MARS
MERCURY
MOON
Atmosphere
Very Active
Active
Active
Very thin
None
Hydrosphere
Very Active
None
Active
Very
inactive
Very
inactive
Very Weak
None
Very weak
None
Magnetosphere Very Active
Lithosphere
Very Active
Active
Active
Very
inactive
Very
inactive
Biosphere
Very Active
None
None?
None
None
Overview of Mars from Earth
• Fourth planet from the Sun.
• Half the size and 1/10 the mass of Earth.
• Characteristic reddish color with light
and dark areas that appear to change
appearance throughout the Martian year
as winds cover and uncover various
surfaces.
• Polar ice caps fade in Martian summer
and grow during the winter.
• Clouds are observed in the atmosphere.
Overview of Mars from Space
• Surface
– Northern hemisphere
• lava-covered plains with volcanoes as large as USA states.
• size possibly evidence against continental drift.
– Southern hemisphere
• strongly cratered, older basalt highlands
– Equatorial region
• gigantic valley near equator: Valles Marineris
• volcanic plateau: Tharsis complex
• Red color from relatively large amount of iron in
surface rocks.
– implies Mars not as differentiated as other terrestrial planets,
has smaller core, no magnetic field.
Overview of Mars from Space
(continued)
• Evidence for liquid water at surface in past
– surface features that resemble Earth’s riverbeds,
sandbars, and floodplains
– permafrost suggested in layering of surface deposits
of sand and ice, as well as in landslides
– polar ice caps contain frozen carbon dioxide and
water ice
– new images suggest recent water at surface in crater
rims near poles.
• Evidence against liquid water at surface in past
– wide-spread deposits of olivine on surface
Properties of Earth, Venus, and Mars
Earth
Venus
Semi-major axis (AU)
1.00
0.72
1.52
Period (Earth yrs)
1.00
0.61
1.88
Mass (Earth=1)
1.00
0.82
0.11
Diameter (Earth=1)
1.00
0.95
0.52
12,756 km
12,140 km
Density (g/cm3)
5.5
5.2
3.9
Surface gravity(Earth=1)
1.00
0.91
0.38
Rotation period
23.9 hrs
Mars
6788 km
-243 days 24.6 hrs
Surface area (Earth=1)
1.00
0.94
0.28
Atmos. pressure(bar)
1.00
90
0.007
Surface magnetic field
(Earth=1)
1.00
1/1000
1/800
Atmospheric Compositions (in %)
of Earth, Venus, and Mars
Venus Mars Earth
Carbon dioxide (CO2)
96.5
95.3
0.03
Nitrogen (N2)
3.5
2.7
78.1
Argon (Ar)
0.006
1.6
0.93
Oxygen (O2)
0.003
0.15
21.0
Neon (Ne)
0.001 0.003 0.002