1. PTYS 214 – Spring 2011  Homework #8 available for download from the class website Due 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

2. 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…

3. 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

4. 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!

5. It is about half the size of Earth (6787 km) It has about 1/3 the gravity of Earth (3.63 m/s 2 ) Mars has the same amount of land as the Earth … but no oceans

6. 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 CO 2 and some amount of N 2, 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)

7. 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

8. Mars today… …is a sterile, alien desert, hostile to life

9. 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)

10. 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

11. What about Mars? Over 3 Gyr ago Earth had simple life

12. 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

13. Temperature triple point boiling Earth gas liquid solid plasma sublimation melting Mars 273 K 10,000  K Pressure 1 bar Water 373 K Problem: Liquid water is unstable under current Martian conditions

14. 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

15. Valley Networks on Mars Ancient Terrains Valleys converge downstream Individual valleys are over 1 km across

16. 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

17. Youngest geologic features Gullies have been identified on the walls of canyons, channels and impact craters Water seepage? New Gullies!

18. Evidence of water ice near the surface (<1 m) Mars Odyssey (2001) Gamma Ray Spectrometer

19. Gamma Rays and Surface Composition Energy of gamma rays is indicative of the element that emits them

20. The history of Mars and its water is recorded in the rocks!

21. “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!

22. Viking, Pathfinder, MER, and Phoenix Landing Sites Cryse BasinElysiu m Mons Hellas Meridiani Gusev Olympus Mons Vallis Marineris

23. Spirit Rover - Gusev Crater Site THEMIS infrared daytime images Basalt rock Gusev Drilled.15 in in the rock with the abrasion tool Patch of nearly pure silica  indication of hot springs?

24. Opportunity Rover - Meridiani Site Few mm up to a cm in size Water-formed hematite?  Plains strewn with hematite spherules (blueberries)  Hematite spherules within bedrock  Bedrock is a sulfate   Deposited in water! Cross-bedding Scallops  Surface water!

25. 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

26. 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)

27. 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 16 O, 17 O, and 18 O 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)

28. 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

29. Evidence of Water in Martian Meteorites  Carbonate minerals - Liquid water flows through fractures in rocks and dissolved CO 2 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

30. 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

31. 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…

32. Quiz Time !