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Transcript of PTYS 214 – Spring 2011 Homework #8 available for download from the class website Due Tuesday,...
PTYS 214 – Spring 2011
Homework #8 available for download from the class websiteDue Tuesday, Apr. 5
Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/
Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Mars http://mars.jpl.nasa.gov/
Announcements
Why is Mars important for Astrobiology?
Relative proximity – first planet where we can realistically test for biological potential and life
Similarity to Earth – It is a rocky, terrestrial planet in the inner part of the Solar system with an atmosphere - yet it is also very different
If life would be found on Mars it may provide a strong argument in favor of life being a common phenomenon in the galaxy, unless…
it may simply prove panspermia…
Telescopes brought beliefs of “canals” and the Martians who could have built them
History of “Martian civilization”“Canals” mapped by Schiaparelli, 1877
Canals mapped by Lowell, 1894
Viking Orbiter, July 1976
Mars Global Surveyor, April 2001
HiRise Camera, April 2007
Let’s not forget about the famous “Face on Mars”
Which is just one of thousands erosional landforms!
It is about half the size of Earth(6787 km)
It has about 1/3 the gravity of
Earth (3.63 m/s2)
Mars has the same amount of land as the Earth… but no oceans
Earth-Mars Similarities Position in the Solar system – Martian orbit is 1.52 A.U.; Earth’s
is 1 AU (Jupiter: 5.2 AU; Neptune: 30 AU)
Bulk chemical composition – Both have a Si-rich crust and mantle, and a Fe-rich core
Size – Mars is about one-half the Earth’s size by radius
Atmosphere – Like Earth, Mars has CO2 and some amount of N2, but NO oxygen (or ozone)
Similar rotation rate – 24.6 hours
Similar axis tilt – 25.2° for Mars versus 23.5° on Earth
Geology is similar on both planets
Plenty of water (on Mars it is mostly frozen)
Earth-Mars Differences
Global-scale plate tectonics − present on Earth, not on Mars
Liquid water − Earth has global oceans on its surface, Mars does not
Atmosphere − Martian atmosphere (0.006 bar) is much thinner than Earth’s ( 1 bar)
Magnetic Field − Earth has one, Mars does not
Mars today…
…is a sterile, alien desert, hostile to life
Problems for life on the Martian surface
Cold (average temperature ~210K) - Why? – not many organisms can grow under these temperatures
Thin atmosphere – open liquid water is unstable
Very little oxygen – no terrestrial-like animal life
Very little ozone – no UV protection
No magnetic field – poor protection from cosmic rays (charged particles)
Could Mars once have had a warm, wet environment for life?
Mars and Earth formed about 4.5 Gyr ago and experienced a similar evolution
What about Mars?
Over 3 Gyr ago Earth had simple life
Follow the water!
Given that the bulk chemical composition of Mars is very similar to the Earth’s we can expect that nutrients and carbon are available on Mars
Even though Mars is further away from the Sun than the Earth, it still receives significant amount of the solar energy – photosynthesis is possible
Therefore, the critical factor for the potential martian biosphere is the presence of liquid water on the surface of Mars
Temperature
triple point
boiling
Earth
gas
liquid
solid
plasma
sublimation
melting
Mars
273 K 10,000K
Pre
ssur
e
1 bar
WaterWater373 K
Problem: Liquid water is unstable under current Martian conditions
Liquid water may have been present on the Martian surface in the past!
Geo-morphological evidence:
1) Features that are similar in appearance to terrestrial water-formed features
2) Degradation (weathering) of ancient impact craters
Mineralogical evidence
1) Minerals deposited in water
2) Water presence
Valley Networks on Mars Ancient
Terrains
Valleys converge downstream
Individual valleys are over 1 km
across
Martian Outflow Channels on Younger Surfaces
Well-defined margins of the channel indicate confined flow
Tear-drop-shaped islands are erosional remnants left behind obstacles
Youngest geologic features
Gullies have been identified on the walls of canyons, channels and impact craters
Water seepage?
New Gullies!
Evidence of water ice near the surface (<1 m)
Mars Odyssey (2001) Gamma Ray Spectrometer
Gamma Rays and Surface Composition
Energy of gamma rays is
indicative of the element that emits
them
The history of Mars and its water is recorded in the rocks!
“EYES”Remote Sensing Package
Pancam Mini-TES
“HANDS”Microscopic Imager
Alpha Particle X-Ray Spectrometer Mössbauer Spectrometer
Rock Abrasion Tool
Mars Exploration Rovers (MER):The robot “geologists”
High Gain Antenna
Low Gain Antenna
UHF Antenna
“FEET”It is mobile (and pretty stable!
Viking, Pathfinder, MER, and Phoenix
Landing Sites
Cryse Basin Elysium Mons
Hellas
Meridiani Gusev
Olympus Mons
Vallis Marineris
Spirit Rover - Gusev Crater Site
THEMIS infrareddaytime images
Basalt rock
Gusev
Drilled .15 in in the rock with the abrasion tool
Patch of nearly pure silica indication of hot springs?
Opportunity Rover - Meridiani Site
Few mm up to a cm in size
Water-formed Water-formed hematite?hematite?
Plains strewn with hematite spherules (blueberries)
Hematite spherules within bedrock
Bedrock is a sulfate
Deposited in water!
Cross-bedding ScallopsSurface water!
Liquid water may have been present on the Martian surface in the past!
Geo-morphological evidence:1) Features that are similar in appearance to terrestrial
water-formed features2) Degradation (weathering) of ancient impact craters
Mineralogical evidence
1) Minerals deposited in water2) Water presence
Mineralogical Evidence:
Martian Meteorites
Pieces of rocks ejected from Mars after impact events and reaching Earth’s surface
Of over 30,000 meteorites found on Earth, only 34 have been identified as Martian meteorites
They are also known as SNC, from the names of the most representative types (Shergotty, Nakhla, Chassigny)
Nakhla(1911)
Chassigny(1815)
How do we know that some meteorites are from Mars?
Age separates them from other meteorites - Almost all Martian meteorites are much younger (180-1300 Myr) than most meteorites, and have a composition similar to terrestrial basalts
Oxygen isotopes separates them from Earth’s rocks - values of 16O, 17O, and 18O are distinct from terrestrial rocks and group all 34 Martian meteorites together
The isotopic composition of gases trapped in the meteorites is almost identical to the Martian atmosphere (comparison with Viking measurements)
Comparison of Mars atmosphere measured from Viking to trapped gases in EETA79001 (Shergottite):
Values are the same!
The impact that ejected the meteorites causes some melting of the rock
The melt cooled very rapidly and formed a glass that trapped atmospheric gases
Atmospheric gases
Evidence of Water inMartian Meteorites
Carbonate minerals - Liquid water flows through fractures in rocks and dissolved CO2 can be precipitated
Hydrated minerals have martian D/H (deuterium to hydrogen ratio)
Electron Microscope image of clay and carbonate (siderite) vein in meteorite Lafayette
ol: olivine
Evidence of Water in Martian Meteorites
• “Rusty” minerals that require liquid water to form
• Some several hundred million years old
they formed on Mars
View of the Lafayette meteorite, 1mm across
Beyond Water: Evidence of life? ALH84001 is a Martian meteorite that became famous
because it appeared to contain structures that were considered to be fossilized remains of bacteria-like lifeforms
More in the next lecture…
Quiz Time !