Chapter 10: Mars A Near Miss for Life?

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Chapter 10 Mars A Near Miss for Life?

• Orbital Properties
• Physical Properties
• Seasons
• Surface Features
• Atmosphere
• Satellites
• Comparison to Earth and Venus

2
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.

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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.

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Superior Planet Configurations
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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

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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.

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Earth-based Studies of Mars

• First telescopic observations by Galileo.
• Small angular size of Mars, Earths 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.

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Mars in Two Views
9
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
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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.

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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.

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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

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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
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Current Mission Mars Odysseyhttp//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.

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Odyssey
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Current Mission Mars Odyssey
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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)
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Mars Statistics

• Satellites 2
• Diameter 6,785 km (0.52x Earth)
• Mass 0.11 x Earth
• Density 3.9 g/cm3 (Moon3.3,Earth5.5)
• 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

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Seasons on Mars

• Mars axial tilt only slightly greater than
  Earths.
• expect seasons similar to Earth.
• Mars orbital eccentricity greater than Earths.
• 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?

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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).

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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 Earths.
• may vary by 30 throughout Mars year because of
  variations in solar heating.
• No recorded lightning or thunder.

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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 (gt100mph)
• At noon in the summertime, surface temperatures
  may reach gt300 K.
• At night,
• temperatures drop up to 100 K,
• convection ceases, and
• troposphere vanishes.

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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.

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Martian Dust Storms
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Martian Dust Devil
animation file///H/phys1050-fall2001/pictures/du
stdevil.gif
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Comparing Terrestrial Atmospheres
PLANET COMPOSITION PRESSURE
Earth Nitrogen/Oxygen 1 atmosphere
Venus Carbon dioxide 100 atmosphere
Mars Carbon dioxide 0.01 atmosphere
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Goldilocks and the 3 PlanetsA story about the
Greenhouse Effect
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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.

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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 9 m 3 km 30 m
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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 9 m
Earth 100 mm 3000 m
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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.

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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.

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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 long-term, repetitive
  climate changes.

N-pole cap
Mariner 9 images
S-pole cap
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Evidence of Water on Mars?
Runoff channels resemble Earths river systems,
4 billion years old
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Water Erosion?
Outflow channel relic of catastrophic flooding
3 billion years ago.
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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)

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Evidence of Water in the Past
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.

• Sedimentary rock layers like these in Mars's
  Holden Crater suggest that the Red Planet was
  once home to ancient lakes.

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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

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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.

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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.

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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.

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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.

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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.

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Crustal Thickness
Red - thin Blue - thick

• Crustal thickness may be inferred from gravity
  observations made by Mars Global Surveyor.

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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.

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Martian Lithosphere
Viking 1 view from surface of Mars
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Surface FeaturesA view from HST
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Terrains on Mars

• Highlands - 60
• 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

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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

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Maps from Mars Global Surveyor Hellas
region
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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)

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Craters on Mars
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Maps from Mars Global Surveyor Utopia region
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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).

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Maps from Mars Global Surveyor Tharsis
region
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Olympus Mons
Largest known volcano in our solar system,
shield volcano with 3 x elevation of Mt.
Everest on Earth
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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
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Alba Patera

• Two views of Alba Patera with topography draped
  over a Viking image mosaic. The vertical
  exaggeration is 101. (Credit MOLA Science Team)

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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 101. (Credit MOLA
  Science Team)

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Valles Marineris

• Discovered by Mariner 9
• On Earth, would stretch from Los Angeles to New
  York

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Valles Marineris The Grand Canyon of Mars
Cause tectonic fracture of crust Length 4000
km Depth to 7 km
Width to 120 km
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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)

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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.

64
NASAs 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

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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.

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Viking 12 ExperimentsA 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.
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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.
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Geologic History

1. Condensation from the solar nebula.
2. Accretion of planetesimals into the planet.
3. Short period of completely molten state.
4. Partial differentiation.
5. Formation of thick rigid crust.
6. Impact cratering.
7. Volcanic and tectonic activity, but no plate
   tectonics.
8. Interior cools.
9. Relatively inactive today, but some
   geologic processes exist.

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Moons of Mars
Irregular shape, pitted with craters, density 2
g/cm3, circular orbits in equatorial plane.
70
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.

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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
Magnetosphere Very Active Very Weak None Very weak None
Lithosphere Very Active Active Active Very inactive Very inactive
Biosphere Very Active None None? None None
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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.

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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.

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Overview of Mars from Space (continued)

• Evidence for liquid water at surface in past
• surface features that resemble Earths 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

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Properties of Earth, Venus, and Mars
76
Atmospheric Compositions (in ) of Earth, Venus,
and Mars