AGA 0316 Aula 15
Buscando a vida fora da Terra:
Marte
Why Mars is important for
Astrobiology?
• Relative proximity – first planet where we can
realistically test in loco for biological potential
and life
• Mars is in many ways similar to Earth. Rocky,
terrestrial planet in the inner part of the Solar
system with an atmosphere. Yet it is also very
different.
• Therefore if life is found there it would be a
very strong argument in favor of life being an
ubiquitous phenomenum in the galaxy
History of Martian “Civilization”
• In 1784 William Herschel (famous for the
discovery of Uranus) claimed that Mars has an
atmosphere and is therefore probably inhabited.
• Giovanni Schiaparelli claimed to see a network of
79 linear channels (canali) in 1877
• Percival Lowell opened Lowell Observatory in
Flagstaff, Arizona in 1894. (claimed to see 200
canals)
• Lowell suggested that canals were built by an
ancient martian civilization.
Giovanni Schiaparelli
William Herschel
Percival Lowell
• In 1965 “Mariner 4” spacecraft send a few dozen good pictures of the Martian
surface – no evidence for intelligent life. Mars is in fact a cold and dry planet!
6
7
9
1960’s
1970’s
1990’s
2000’s
Spirit + Opportunity
Mars Fact Sheet
Parameter
Diameter
Average Distance From the Sun
Average Temperature
Mean Density
Rotational Period
Mean Atmospheric Pressure
Surface Gravity
Tilt of Axis
Orbit period
Value
6787
1.524
210
3.94
24.6229
0.007
3.63
25.2
687
Atmospheric Components
Element
Carbon Dioxide
Nitrogen
Argon
Water
Symbol
CO2
N2
Ar
H2O
Percentage
95.32
2.7
1.6
0.03
Units
km
AU
K (-81 F)
g/cm3
hours
bars
m/s2
degrees
days
EARTH’S Atm
CO2 0.04%
N2 78,1%
Ar
0.93%
H2O 0 – 4 %
Earth-Mars Similarities
• Position in the Solar system – Martian orbit is 1.5 A.U.;
Earth’s is 1 A.U. but Neptune’s is 30 A.U.
• Similar bulk chemical composition – Si-rich crust and
mantle and Fe-rich core
• Size – Mars is only twice smaller than Earth by radius
• Atmosphere has greenhouse gas (CO2) and some
amount of nitrogen
• Volcanoes
• Similar rotation rate – 24.6 hours
• Plenty of water (frozen; subsurface?)
Earth-Mars Differences
• Earth has a global-scale plate tectonics, Mars
does not.
• Earth has global oceans at its surface, Mars has
not
• Martian atmosphere (0.007 bar) is much
thinner than Earth’s ( 1 bar)
• Earth has an intrinsic global magnetic field,
Mars has not
Problems for life on the Martian surface
• Cold (average temperature ~220K); not many
known organisms on Earth can grow under these
temperatures
• Thin atmosphere – open liquid water is unstable
• Very small amount of oxygen – no terrestrial-like
animal life
• Very little ozone – no UV protection
• No magnetic field – poor protection from the
cosmic rays
Problem
Water does not have a liquid phase under current
low Martian pressures. Ice sublimates to water vapor
directly.
However, there are strong evidence that liquid water
was present in the past on the Martian surface
Evidence for liquid water on the Martian surface
• Geomorphological evidence:
1) Look for features that are similar in
appearance to terrestrial water-formed features
2) Degradation (weathering) of the ancient
impact craters (erosion)
• Mineralogical evidence
MARTIAN SOIL
FLOOD TRACES ON CRATER WALLS
Valley network on the ancient terrain of the martian
surface. Notice that valleys converge downstream.
Individual valleys are about a kilometer across.
Flood channel occurring on a relatively young
surface. Note the well-defined margins of the channel
indicating confined flow and the streamlined, tear-dropshaped islands where erosional remnants have been
left behind obstacles.
Even the youngest features on Mars appear to show
evidence for liquid water. Gullies have been identified
on the walls of canyons, channels and impact craters.
Most likely were formed by seepage of water from
within the crust.
Martian Meteorites
• Meteorites which originated from Mars –
impactors hit Martian surface and some small
fraction of the ejected rock can arrive on Earth
• Although > 31,000 meteorites were found,
only 34 have been identified as Martian
meteorites
How do we know that some
meteorites are from Mars?
• Age. Almost all martian meteorites are relatively
young volcanic rocks (180-1300 Myr) with
composition similar to terrestrial basalts
• Oxygen isotopes are distinct (16O, 17O, 18O) from
terrestrial rocks and group all 34 meteorites together
• The isotopic composition of gases trapped in the
meteorites is almost identical to the Martian
atmosphere (comparison with Viking
measurements).
The oxygen isotopic compositions of rocks from Earth, Mars, and the asteroid
Vesta, the largest asteroid that melted, define three parallel lines on this plot
of 17O / 16O vs. 18O / 16O. The lines are parallel because on each body the
oxygen isotopes were separated according to their masses, when the rocks
formed.
Classification of Martian meteorites
(SNC: shergottite, nakhlite, and chassigny )
• 1 billion tones of Martian rocks crashed into Earth
!
• Shergottite (Shergotty meteorite from India,
1865) - 25
• Nakhlites (Nakhla meteorite from Egypt, 1911) - 7
• Chassignites (Chassigny meteorite from France,
1815) - 2
Evidence of water in SNCs
• Carbonate minerals. Liquid water flows
through fractures in rocks and dissolved CO2
can be precipitated.
• Hydrated minerals with martian D/H
Electron Microscope image of clay and
carbonate (siderite) vein in Lafayette
section. ol olivine.
ALH84001
• Shergottite which containes structures that
were considered to be the fossilized remains
of bacteria-like lifeforms.
Viking Mission
• Two orbiters, two landers
• Two landers landed on the opposite sides of Mars in
1976
• The Viking 1 Lander touched down at 22.7° N
latitude and 48.2° W longitude
• The Viking 2 Lander touched down at 48.3° N
latitude and 226° W longitude
Viking Results
• Viking carried 4 instruments
designed to detect any sign of
biology:
• The Labeled Release (LR), Gas
Exchange (GEX), and Pyrolytic
Release (PR) experiments, all
designed to detect existent life
on Mars.
• The Gas Chromatograph/Mass
Spectrometer (GC/MS) was
capable of detecting organics
at a level of a few parts per
billion (ppb)
Pyrolytic Release experiment (PR)
• Martian soil was put in a chamber and
exposed to CO2 and CO mixture
• CO2 and CO were labeled with 14C
• Idea: “If biota were in the soil it would
incorporate some CO2 or CO and convert it to
organic material”
• Heat the soil  break organic material  look
for release of 14C
Gas exchange (GEX)
• Martian soil was put into a chamber and
mixed with plenty of different nutrients
(amino acids, glucose, salts, vitamins ..)
• Look for H2, N2, O2, CH4, CO2,and Ar, Kr (for
calibration) released from the soil (bacteria?).
Labeled release (LR)
• Martian soil was put into a chamber and
mixed with nutrients (glucose and sulfate)
enriched in 14C and 35S
• Look for gas release enriched in 14C and/or 35S
(released by bacteria?)
LR - TSM
Biology Package
• What the Viking biology experiments found:
Experiments
Response for
sample
Expected
Response for
sample w/
Biology
Response for
heatsterilized
control
Expected heatsterilized
Control
Response
GEX
oxygen emitted
oxygen emitted
oxygen emitted
none
LR
labeled gas emitted
labeled gas emitted
none
none
PR
carbon detected
carbon detected
carbon detected
none
• The GC/MS detected no organics above the 10 ppb level
What we expected
• This was surprising as each
year, 2.4 x 108 grams of
reduced (organic) carbon is
delivered to Mars each year
by meteors, which should
have been detectable by the
Viking GC/MS.
• Even without life, organics
were expected.
• With regolith mixing to a
depth of 1 km, organics
should be present at about
500 ppb.
Viking Conclusions
• It was concluded that the Martian surface is rich
in UV-produced oxides and superoxides at the
ppm level, which destroy any organics present.
• This conclusion reconciles the apparently
contradictory results of the other Viking life
experiments.
• However . . .(cf. OH-based life)
The Atacama desert
• Gonzáles et al. use the
oxidizing soil and hyperarid conditions in the
Atacama Desert as an
analog for the Martian
surface.
• They analyzed the
Atacaman soil with a
GC/MS to compare with
Viking results.
What they found
• In the most arid sample, both formic acid and benzene
were found when pyrolized at 750ºC.
• However, Viking pyrolysis temperatures maxed out at
500ºC, so . . .
• Using the Viking pyrolysis temperature, the formic acid
detected was reduced by a factor of 4 and there was no
benzene detected at all.
formic acid
benzene
• All three Viking’s experiments assumed that
we would be able to culture potentially
present martian organisms.
• Even on Earth only 1 in 100 organisms can be
cultures at best.
• Viking results do not rule out the possibility of
life in the martian soil.
• Is there another way to discover martian life?
Arguments in favor of “life on Mars”
from ALH84001
• Presence of polycyclic aromatic hydrocarbons
(PAHs). PAHs can form as decay products of
microorganisms
• Presence of magnetite crystals whose
structure is very similar to crystals produced
by some terrestrial bacteria
• Ovoid structures in carbonate globules similar
to terrestrial microbes
PAHs
Magnetite crystalls
(Fe3O4)
Carbonate globules (50-250 m)
Ovoid structures (20-100 nm)
History of ALH84001
• Age ~4.5 Gyr old (rock crystallized)
• Carbonate globules are ~3.9 Gyr old
• Rock remained on the surface of Mars until 16 Myr
ago when it was ejected
• Meteorite was captured by Earth 13,000 years ago
and fell into Antarctica
• Covered with snow and
ice until 700 years ago
• Recovered in 1984
Summary of ALH84001
• Most of the morphological fossils are thought to be
too small to represent living organisms
• Most of the organics are terrestrial in origin and the
martian organics could have been produced by
nonbiological processes
• The magnetite grains are thought to represent the
strongest evidence for life
• McKay et al. found fossil like structures in other
Martian meteorites (Nakhla 1.3 Gyr and Shergotty
165 Myr)
Can martian biota “hide” in the
terrestrial biosphere?
• Primitive life is very resilient. Some bacteria can grow
under -15 C (and lower). Some bacteria has tolerance
to extreme desiccation. Some bacteria are tolerant to
UV and ionizing radiation.
• Suppose a microorganism from
Mars survived a trip to Earth
• How would we distinguish
between martian and terrestrial
bugs?
One possible clue is the ability to adapt to environments that
could never have happened on Earth. (Pavlov et al., 2006)
Radioresistance – tolerance to ionizing radiation
(p.n,-rays)
High radioresistance - totally unnecessary ability
on Earth. Why are there bacteria like that on
Earth? Why were them selected on Earth?
Radioresistance
1. Extremely radioresistant bacteria :
Deinococcus radiodurans , Rubrobacter radiotolerance, Rubrobacter
xylanophilus, Chroococcidiopsis, Termococcus gammatolerance.
Radioresistance is 100-1000 times higher than in other microorganisms
2. High doses of ionizing radiation create a lot of DNA damages and
radioresistant bacteria have an unknown and unique mechanism for DNA
repair (more 100 double strand breaks)
3. Lethal radiation dose >> dose accumulated during the lifetime of the
radioresistant bacteria (by 10 orders of magnitude). Time of accumulation of
the lethal doses is 106 – 108 years.
Totally useless on Earth!
Hypothesis
• Radioresistant bacteria originated on Earth
• Bacteria was transferred to Mars by meteorites
• On Mars microorganisms acquired
radioresistance ability
• Radioresistant bacteria were transferred back
to Earth by Martian meteorites
0
lg S
-1
-2
-3
-4
-5
0
2
4
6
8
10
12
D o s e (k G y )
Gamma radiation survival curves of the Еscherichia coli (rhombus) and
Deinococcus radiodurans (squares) (Battista et al, 1999). S – surviving
fraction of the bacterial population
1 Gy = 1 J/kg
5 Gy is lethal for humans within two weeks
Background radiation on Earth: 0.0005 Gy/year
Experiment with Deinococcus Radiodurans at LNLS
(Lima et al. 2009)
Why Mars?
Great oscillations in Martian obliquity (period 1.2x105 years) 
oscillations of annual insulation of the polar regions  dramatic
regular oscillations of global climate and atmospheric mass  long
periods of the “frozen state” for subsurface layers  long periods
of the bacterial dormancy
Low atmospheric mass , no magnetic field  Irradiation of cosmic
rays in subsurface layers of Mars 100-fold of the terrestrial
irradiation  Periods of sublethal doses accumulation 104 years.
 Total time of “training process” (100 cycles) 106 years
Problem with Martian climate
• Plenty of frozen water in the shallow
subsurface (Mars Odyssey)
• Evidence of the “open” liquid water on the
early Mars (Martian meteorite, Water-formed
features)
• How did early Mars manage to maintain liquid
water on its surface?
Hydrogen abundance from Mars Odyssey observations
Global map of Mars in epithermal (intermediate-energy) neutrons. Odyssey mapped the
location and concentrations of epithermal neutrons knocked off the Martian surface
by incoming cosmic rays. Deep blue areas at the high latitudes mark the lowest levels
of neutrons, which scientists have interpreted to indicate the presence of high levels
of hydrogen. The hydrogen enrichment, in turn, is suggestive of large reservoirs of
water ice below the surface.
Challenge for the early warm
Mars could be much worse.
CO2 can condense in the polar
regions at the ground!
Sink for CO2 – volcanoes cannot
compensate. Carbonate silicate
feedback breaks down.
30% CO2 Atmosphere would
start to condense at 200K (-73 C)
Suggested solutions for the early
Mars
• Additional greenhouse gas (CH4). But! It is hard to
justify high levels of CH4 on Mars.
• Water was liquid on Mars only after a strong impact.
However, some features required millions of years to
form and warming effects from impact can not last
that long.
• Mystery of the warm and wet early Mars remains
unresolved ….
Phoenix Scout Mission Overview
• Scouts were designed to
be relatively low-cost and
innovative complements
to NASA’s Mars
Exploration Program.
(Total cost ended up being
about $420 Million)
Phoenix’s Descent
Landing ellipse size compared to
Earth
Science Operations Center
Engineers in the Payload Interoperabilit
Testbed testing the rasp technique on Sol 50
Surface Stereo Imager
PHOENIX LANDED ON MARS
ICE SUBLIMATION ON MARS
Robot: Self Portrait
First Images
Exposing Water Ice
Touching and Tasting Mars
Working Together SSI & RAC images RA scoop with sample going
to the Optical Microscope.
Deliveries to OM, WCL, and door open for next TEGA
What Phoenix discovered?
• General
– confirmed the hypothesis based on orbital data that there
is shallow subsurface water ice on Mars!
• Two different types of ice within ~1m. Why?
• WCL (Wet Chemistry Laboratory)
– Found perchlorate (ClO4-) in the Martian soil. Totally
unexpected. Perchlorate is harmful to humans, but is used
as a source of energy by some microbes.
– Also found other chemicals used by life (K, Na, etc.)
– Slightly alkaline pH (exact number still being worked on – a
little higher than 7)
What Phoenix discovered?
• TEGA (Thermal and Evolved Gas Analyzer)
– Carbonates on Mars! – Can’t quantify this yet, but we definitely
saw carbonates, which has implications for past climate and
perhaps liquid water. Very high probability of Calcite, possibly
other carbonates as well.
– Much less sulfur than we expected. Can’t explain this yet.
• Weather (MET and SSI)
–
–
–
–
–
Snow on Mars!
Saw dust devils in Martian arctic.
Frost formation and fog
Water ice clouds and dust storms
Martian arctic temperatures and pressures for ~150 days
• Soil Properties
– Very sticky
– Very cloddy in some areas
CURIOSITY: amarrissagem em 06/08/2012
CURIOSITY: 1ª foto
CURIOSITY em testes
CURIOSITY DESCENDO SOBRE MARTE
CURIOSITY local da descida: cratera GALE
CURIOSITY: esquema de descida
CURIOSITY RESULTS
http://www.extremetech.com/wpcontent/uploads/2013/09/curiosity-mars-water-contentSAM.jpg