Life on Mars
George Lebo
24 October 2012
AST 2037
1
Life on Mars??
Mars has long been a
“favorite” location
for extra-terrestrial
life
2
Why Mars?
• Mass ~0.1 Earth-mass (0.38 g)
• Radius ~0.6 Earth radius
• Axis tilt
3
Why Mars?
• Seasonal variations and polar
caps
4
Water on Mars
• Polar caps seem to indicate
water (??)
• Schiaparelli finds “canals” (!)
• Percival Lowell, founder of the
Lowell observatory, also
“sees” canals. No one else can.
• Apparently, not just plant life
on Mars, but intelligent beings
with large-scale irrigation for
agriculture !!
• C.S. Lewis wrote “Out of the
Silent Planet” based on this
premise.
• In 1965 the Mariner IV
Spacecraft photos erased all
doubt. The “canals” on Mars
don’t exist.
5
Hold on a second …
• Other people see similar shapes
on Mars … but no “canals”!
6
Mars Atmosphere
• Mostly CO2 (OK …)
• About 0.6% of the atmospheric pressure of Earth (!)
(We knew this from the occultation of stars long before
we sent spacecraft.)
• Temperatures can reach about 65 F
• But, mostly more like -150 F
• At those temps, CO2 freezes (dry ice)
7
Polar Caps: Redux
• So … could polar caps be dry ice instead of H20?
• YES!!
• In fact, the albedo (reflectivity) of the caps is too high for
water ice, but matches dry ice nicely
• Also, we can measure temps when caps recede/grow 
too cold for water, but matches dry ice
• Now … there IS water ice on the caps too, under the
layer of CO2 ice
• But … most of the seasonal variation is in dry ice
8
Seasons: Redux
• The “darkening” spread from
poles to equator is probably due to
dry ice “melting” (reducing the
albedo of that region)
• But … dry ice doesn’t melt – it
sublimes (goes straight from solid
to vapor form)
• Still disappears and changes
albedo
• What else … ?
9
Canals: Redux
• Closer inspection (with photographs!): no evidence for
canals
• In fact, at this low pressure, water sublimes as well  no
liquid water on the surface of Mars!
10
Mars Overview
•Slightly smaller than Earth
•Rotation period is 24.6 hours close to Earth
•Equator inclined at 24 degrees close to Earth
•Very little atmosphere - 1/150
the pressure of Earth
•CO2 (95.3%),nitrogen (2.7%),
argon, oxygen, CO, water vapor
•Two very small moons
11
History of Mars Missions
• The U.S. NASA Mars
• Of 38 launches from
exploration program
Earth in an attempt to
has had a somewhat
reach the planet, only
better record of
19 succeeded, a
success in Mars
success rate of 50%.
exploration, achieving
Twelve of the
success in 13 out of 20
missions included
missions launched (a
attempts to land on the
65% success rate), and
surface, but only seven
succeeding in six out
transmitted data after
of seven (an 86%
landing.
success rate) lander
missions.
Mars – Space Craft Exploration
•1965 – Mariner 4, 6 and 7 “fly
by” Mars
•1971 – Mariner 9 orbits and maps
Mars in detail
•1976 – Viking 1 lands on Mars
•1997 – The Mars Pathfinder places a small
rover called “Sojourner” on Mars
•2004- Spirit (now stuck) and Opportunity
•2009- Curiosity
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Pathfinder Lander
Mars Pathfinder, Twin Peaks
Mars Pathfinder, Large
Crater
Mars Pathfinder, Matterhorn
Mars Pathfinder, Barnacle Bill
Mars Pathfinder, Yogi
Mars Pathfinder, Rover
Foreground
Mars’ Surface
•Polar ice caps – frozen CO2
•Northern hemisphere is rolling
volcanic planes (a)
•Like lunar maria but larger
•Few craters – young (3
billion yrs old)
•Southern hemisphere is heavily
cratered highlands (b)
•Older (4 billion yrs old)
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The Tharsis Bulge is
the major
geographically feature
on Mars
•Roughly the size of
North America
•Lies on the equator
•10 km high
•Less heavily cratered
•Young (2-3 billion yrs)
•Wide depressions
(valleys) lie to east and
22
west
Valles Marineris
• runs for almost 4000 km along
the Martian equator (one-fifth of
the way around the planet!)
• 120 km across at its widest
• 7 km deep in places
• our Grand Canyon would
easily fit into one of its side
"tributary" cracks
•NOT caused by water - due to
stretching and cracking when
Tharsis bulge formed
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VALLES MARINARIS
Analysis of rocks on Mars show they are iron rich
- iron in the soil and oxygen in the atmosphere produce
iron oxide
RUST
•Mars Pathfinder robot
Sojourner
•Highly successful mission
which sent back lots of
pictures of the Martian
landscape
•1999 Mars Polar Lander
failed to make contact
25
Volcanism on Mars
•Largest volcanoes in the solar system are here
•Shield volcanoes (gently sloping edges formed by low
viscosity lava
•None are known to be currently active but eruptions
occurred 100 million years ago
Mars has a surface gravity only
40 percent that of Earth, and its
volcanoes rise roughly 2.5
times as high because of this.
Olympus Mons on Tharsis slope26
Olympus Mons
370 miles diameter, 14 miles high, 5 mile high
cliff at base
AVALANCHE ON MARS
Water on Mars?
Yes – but long ago
About 4 billions years ago Mars had a thicker
atmosphere, warmer surface, and liquid water.
Runoff channels
•Found in southern highlands
•Extensive river systems (like Earth)
•Carried water from highland to valleys
Outflow channels
•Caused by flooding
•Found at the equator
•Formed about 3 billions year ago
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What happened to the water?
• 4 billion years ago - Martian climate begins to change
• Running water (that formed runoff channels) freezes into
permafrost (water ice just below surface) and polar caps
• Remains frozen for a billion years
• Volcanic activity heats large
regions of the surface
• Melts the permafrost
• Flash floods create outflow
channels
• Volcanic activity slows down and
water refreezes
30
The Moons of Mars
Mars has two very small moons discovered in 1877
•Phobos – 28 x 20 km
•Deimos – 16 x 10 km
•Less dense than our Moon or other terrestrial world
•Probably not made of the same material as Mars
Origin – captured asteroids
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Modern Search for Life on Mars
• What could we see from Earth?
• Radio signals (communication)
• But only present on Earth itself for <100 years
• Look for O2
• O2 aggressively combines with rocks on a short
timescale
• So … do not expect free O2 in large amounts (unless
life replenishes it in atmosphere)
• Not much seen on Mars
• Look for methane
• UV solar radiation breaks it down on short timescale
• So … do not expect free CH4 in large amounts (unless
life replenishes it in atmosphere)
• Not much seen on Mars
32
Viking & Life on Mars
• Two Viking landers arrived
at Mars in 1976
• Identical landers, both
stationary (no rover)
• Cameras and various
sensors
• Included several exobiology experiments to look
for life
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Viking: Atmosphere/Soil Tests
• Atmosphere analysis showed no evidence for methane or
silane (SiH4)
• Soil tests
• Take a Martian soil sample and bake it
• Look for amino acids, or other carbon compounds
• Did not find ANY (!)
• So little carbon, scientists struggled to explain why
(less than the Murchison meteorite)
• Theory: UV rays plus CO2 produce oxygen
temporarily; this oxygen breaks down organic
compounds at the surface of Mars, so none left
34
Viking: Gas Exchange
• Take Martian soil, add
“chicken soup” (broth of
yummy nutrients)
• Wait a few days and check to
see if the composition of the
gas changes due to
respiration/metabolism
• Cool result: found evidence
of oxygen enhancement after
nutrient exposure!!
• But: repeat experiment after
“cooking” soil to sterilize it
 same result  !
35
Viking: Labeled Release
• Take Martian soil, add nutrients
with “normal” C12 replaced by
radioactive C14
• Wait a few days and check to see if
C14 shows up in gas due to
respiration/metabolism
• Cool result: found evidence of C14
enhancement after nutrient
exposure!!
• But: repeat experiment  reaction
stops  !
• Explanation: hydrogen peroxide in
soil reacts to release C, but gets
used up in first round of reactions
36
Viking: Pyrolitic Release
• Problem with previous
experiments: what if “yummy”
nutrients for Earth life is notyummy for Martians?
• Add C14-labeled gas to Martian
atmosphere w/Martian soil
• Pump out atmosphere; heat up soil
to break down & release volatiles;
look for C14
• If any found, it must have been
metabolized from gas into
something in the soil
• Cool result: found evidence of
C14!!
37
Viking: Pyrolitic Release
• But …
• Skeptical at this point aren’t we?
• Try this experiment on Earth in
sterilized soil, but with naturally
occurring organic compounds
• Find similar results
• So … no real proof of life
38
Viking: Life on Mars?
• All 3 Viking exo-biology experiments showed “success” in
finding evidence of life
• But … most were inconsistent after further testing
• The pyrolytic release experiment is consistent with life –
but also consistent with no life
• Inconclusive …
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Life on Mars: ALH 84001
• Meteor found in Allen Hills, Antarctica in 1984
• One of 14 meteorites on Earth thought to originate as a
Martian rock
• What ?!
40
ALH 84001
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Life on Mars: ALH 84001
• Basic idea:
• Asteroid hits Mars,
knocking chunks of
debris (including
Mars rocks) into
space
• Rocks wander
around space for
awhile
• Some rocks get
captured by Earth
gravity, and land as
meteors
• It could happen …
42
ALH 84001 Martian Origin
• Isotope abundances change depending on origin point
(distance from Sun)
• Isotope abundances in these meteors closely match Mars
• Pockets of gas in ALH84001 match composition of Mars
atmosphere (90+% CO2; 3% N2; etc.)
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ALH 84001 Timeline
• Radio-isotope dating (as for Earth rocks) implies rock formed
about 4.6 billion YA; igneous  from volcano
• C14 dating of surface indicates it has been on Earth for about
13,000 years
• Weird isotopes indicate exposure to cosmic rays for a
duration of 16 million years
• Timeline:
• 4 GYA rock forms on Mars (some evidence that it came
from Valles Marineris region)
• 16 MYA rock blasted into space, exposed to cosmic rays
• 13,000 YA rock lands in Antarctica
44
ALH 84001: Life on Mars
• 4 pieces of evidence for Martian life embedded in
ALH84001
• Carbonate nodules
• Crystals of iron pyrite
• Traces of polycyclic-aromatic hydrocarbons (PAHs)
• Fossils!
45
ALH 84001: Carbonate
• Carbonate globules are present in ALH84001; formed in
water medium ~1 GY after rock matrix
• These are often created in Earth rocks by life (bacteria)
• Metabolism converts CO2 plus minerals into carbonate
• Could be a sign if life …
46
ALH 84001: Iron Pyrite
• Very small iron pyrite grains are present inside the
carbonates in ALH84001
• These are often created in Earth rocks by life (bacteria)
• Could be a sign if life …
47
ALH 84001: PAHs
• Complex hydrocarbons – building blocks of life on Earth!
• Could be a sign if life …
48
ALH 84001 Fossils!
• Electron microscopy
reveals what appear to be
fossil nanobacteria in
ALH84001 carbonate
globules (!!!!)
• Life on Mars!
• Bill Clinton even has a
press conference to
announce it!
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ALH 84001 Fossils!
E Coli on Earth
Fossil from Mars
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ALH 84001: Really “Fossils”?
• Caveats to ALH84001 scenario
• Carbonates can also form non-biologically; typically at
high temperatures
• ALH84001 pyrites can also form non-biologically, and
small fracture evidence indicates high temperature (!)
• PAHs are found on meteors in general
51
ALH 84001: Really “Fossils”?
• The ALH84001 fossil is
TINY compared even to
small bacteria on Earth
– not sure life can be
that small
• Some indication that the
sampling process for
microscopy may have
CREATED the “fossil”
structures
• Still could be fossils, but
…
52
ALH 84001: Life on Mars?
• Intriguing evidence
• But … none of it is really solid; alternate (non-biological)
explanations seem to work too
• Jury still out …
53
Mars Missions & Life on Mars
•
•
•
•
Anything new?
Water on Mars Redux
Find evidence of shorelines
There WAS standing water on
Mars at some point
• But, when? How long? Could
these have been
volcanic/meteoric melt of
permafrost, lasting a few
years/centuries?
54
Future Searches for Life on Mars
• What next?
• Future Mars missions include more advanced “biology
labs” on rovers
• Also include “sample return” missions, to bring Mars
material back to even more advanced labs on Earth
• Will we find Life (or fossil life) on Mars? Stay tuned …
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PHOENIX LANDER MAY
2008
MARS LANDING SITES
PHOENIX ON MARS
ICE ON MARS
MARS’ ROVER CURIOUSITY
LANDED AUGUST 6, 2012