Transcript Quantum Well Electron Gain Structures and Infrared

Life on Mars - II
Stephen Eikenberry
11 October 2012
AST 2037
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Life on Mars??
Mars has long been a
“favorite” location
for extra-terrestrial
life
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Modern Search for Water on Mars
• http://www.youtube.com/watch?v=Hah5c_kTqh0&feature=r
elmfu
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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
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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
• Irony: first active test for life on Mars by humans
would first KILL any life it finds …
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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  !
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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
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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!!
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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
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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 meteors on Earth thought to originate as a
Martian rock
• What ?!
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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 …
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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
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ALH 84001: Life on Mars
• 4 pieces of evidence for Martian life embedded in
ALH84001
• Carbonate nodules
• Crystals of iron pyrite
• Traces of poly-aromatic hydrocarbons (PAHs)
• Fossils!
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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 …
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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 …
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ALH 84001: PAHs
• Complex hydrocarbons – building blocks of life on Earth!
• Could be a sign if life …
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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
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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
…
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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 …
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Mars Missions & Life on Mars
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•
•
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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?
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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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