1. Announcements ● Passing out marks-so-far today with assignments ● ½ of available marks now given out ● Can always do `bonus assignments' (worth 2 credits) – Find current news article relevent to the course (1 credit) – Briefly describe it and its relevence to the course (1 credit)

2. The Search: Mars ● A Short Biography of Mars – The Planet and its History ● The History of Mars Exploration – Past – Current – Future? ● The Search for (past) Life on Mars – Viking Experiments – Microbial Fossils

3. A Portrait of Mars as a Small Planet ● Mars ● The atmosphere of Mars ● How it came to be that way

4. Mars ● Red planet between Earth and Asteroid Belt ● Half again as far away from Sun as the Earth is – Expect it to be ~100 o F colder than Earth on average – Average too cool for water – Peak temps ~ 70 o F (but -130 at night!)

5. Mars ● Near asteroid belt – Likely more collisions than Earth ● Large impacts can blow off significant rocky material – Meteorites ● As well as gases (atmosphere)

6. Mars ● ~1/2 radius of Earth ● ~1/10 mass ● ~40% surface gravity – Force of a 1 lb weight less than ½ lb on Mars – Less gravity holding the atmosphere in place

7. Mars ● Too little gravity to be able to hold onto a significant atmosphere ● Atmospheric pressure less than 1% of Earth's

8. Evaporation ● What causes evaporation of liquid, and what prevents it?

9. Evaporation ● Fastest moving water (say) molecules can escape into atmosphere ● Water molecules in atmosphere can collide into water and become part of the liquid ● Balance is reached when evaporating water = condensing water

10. Evaporation ● Can change balance: – Little water in atmosphere, evaporation happens faster ● (Why feel so sticky on a humid day) – If air pressure is very low, evaporated water molecules can move very far away from pool of water ● Fewer around to condense ● Faster evaporation

11. Evaporation ● Effect of atmospheric pressure happens on our own planet ● Reason for `high-altitude cooking instructions' on some boxes ● Higher altitude -> lower air pressure -> evaporation is easier - > lower boiling point

12. Evaporation ● Martian atmospheric pressure < 1% of Earth's – (Earth's atmosphere at 15 miles / 80,000 ft) ● Water boiling point is so low that any liquid water evaporates immediately ● No free water possible on surface

13. Evaporation ● But water ice DOES exist on Mars: – Polar ice caps ● Mostly (on top) dry ice (frozen CO2) ● Underneath, visible when CO2 has sublimated, water ice – Quite likely some trapped under surface: `permafrost'

14. Atmospheric Pressure ● Atmospheric pressure is seasonal ● Dry ice caps melt – Increase CO 2 in atmosphere – Increase atmosphere pressure ● Dry ice caps re-freeze – Pressure decreases

15. The Reasons for the Seasons ● Earth's (and Mars') axis is tilted ● Earth: 23.5 o (Mars: 25.9 o ) ● Tilt stays in same direction as planet orbits Sun

16. The Reasons for the Seasons ● Sun comes in at different angle when planet is at different positions ● Summer: – Light most direct – Sun closest to being overhead ● Winter – Comes in at angle: ● Same amount of light covers larger area – Increased reflection Summer Winter

17. The Reasons for the Seasons ● Orientation changes over course of year ● Another effect: Earth is slightly further from Sun in (Northern Hemisphere) Winter than in Summer – Only ~1% effect (5 o F) – Effect of orientation ~16% effect (90 o F) Fall: Cubs win (effective 2003) Spring: Bulls Lose Winter: Bears Lose

18. Ecliptic ● Because of Earth's tilt, equator (and rotation) do not line up with plane of the solar system ● Solar system objects (Sun, Moon, planets) apear to lie along an arc – ecliptic

19. Ecliptic ● Planets are along plane of solar system ● Appear on Earth to along an arc ● Mars visible these days early at night towards the East, even from Chicago – Bright reddish `star' – Near a bright greenish- yellow `star' (Venus) Starmap for tonight, 9pm

20. How Mars Came to Be This Way ● Distance from Sun makes global liquid water difficult but not impossible ● NO ATMOSPHERE – Liquid water quickly evaporates – No greenhouse effect to warm planet, regulate temp. – No ozone to protect from UV Large Enough for Atmosphere Not Large Enough for Atmosphere

21. The History of Martian Exploration ● Past explorations ● Current Rover Missions ● Future Plans

22. Exploration of Mars Today ● So many recent missions to Mars that it's becoming almost anticlimatic ● News filled with discoveries from current rovers ● Still very difficult: – Success rate low! – Scientists can't go there at whim yet

23. Observations of Mars from Earth ● Early telescope observations: – `observations' of canals – Improved telescopes showed this not to be the case ● Later, radio observations – Surface temperature – Crude radar maps of surface

24. 1960-2: Korabl (`Marsnik') ● Attempted Russian Probes ● 4 attempted flybys, 1 attempted landing ● Most barely made it past Earth orbit, one was lost between Earth and Mars

25. 1964: Mariner, Zond ● Mariner 3, 4 (USA): attempted flyby – Mariner 3: Couldn't make it to Mars – Mariner 4: First flyby, close up pictures ● Zond 2 (USSR): Russian flyby, descent – Lost on its way to Mars

26. 1969: Mariner, Mars 1969 ● Mariner 6,7: Identical flyby craft – Mariner 4: First flyby, close up pictures ● Mars 1969A/B: Russian flyby, descent – Didn't survive takeoff

27. 1971: Mariner, Mars 2/3: Orbiters ● Mars 2/3 (USSR): First orbiter of another world – Measured temps, magnetic fields – Sent probe, 1 crashed too fast, other survived 20 hours Mariner 8 didn't make it ● Mariner 9: Orbited, obscured by storms – First close-up views of moons of Mars

28. 1973: Mars 4/5/6/7 (USSR) ● Mars 4: Brakes didn't work; flew by instead of orbited ● Mars 5: Successful Orbit, pictures ● Mars 6: Descent, sent data from atmosphere before shutting down, but data garbled ● Mars 7: Missed Mars entirely

29. 1975: Viking 1,2 (USA) ● Identical Orbiter + lander – Orbiters searched for safe landing places – Extensive weather measurements, chemistry/biology experiments – Sent several thousand images, data

30. 1988: Phobos 1,2 (USSR) ● Lost due to human error (Phobos 1), computer malfunction (Phobos 2)

31. 1988-1992 ● 1988: Phobos 1, 2 (USSR) – Lost due to human error (Phobos 1), computer malfunction (Phobos 2) ● 1992: Mars Observer (USA) – All contact lost 3 days from Mars

32. Very Recent Mars Missions ● 1996: – Mars 96 (USSR): Didn't successfully leave Earth – Mars Global Surveyor (USA) ● Looking for places to send Pathfinder ● Still sending back data – Mars Pathfinder ● Probe with some sensors ● Test of new technologies, techniques

33. 1998: Less Successful ● Nozomi (Japan) – Navigation problems – Could not reach Mars at expected time – Unable to orbit Mars ● Mars Climate Orbiter (USA) – Crashed into Mars after mistake in converting units in probe computer programming

34. 1998-9: Less Successful ● Nozomi (Japan) – Navigation problems – Could not reach Mars at expected time – Unable to orbit Mars ● Mars Climate Orbiter (USA) – Crashed into Mars after mistake in converting units in probe computer programming ● Mars Polar Lander (USA) – Signal lost near Mars: Navigation errors?

35. 2001: Mars Odyssey (NASA) ● Orbiter ● Build global map of telements, minerals on the Mars surface ● Determine the abundance of hydrogen in subsurface. -> hidden deposits of water ice? ● Structure of the Martian surface. ● Radiation environment between the Earth and Mars and in low Mars orbit (radiation-related risk to human exploration) ● Communication relay Spirit/Opportunity/Beagle

36. 2001: Mars Express (Europe) ● Orbiter + Lander/Rover (Beagle) ● Beagle lost ● Image globe in 3D ● Build accurate picture of meteorology/climage ● Communications Relay

37. 2003: Spirit, Opportunity (USA) ● Search for/study many types of rocks and soils that might hold clues to past water activity. ● Maps showing the locations of different kinds of rocks and soils around the landing sites. ● What forces have shaped the landscape ● Search for minerals that contain water/formed in water. ● Identify minerals, how made ● Clues to what environment was like in past

38. The Search for Life on Mars ● Pictures of surface ● Viking biology experiments ● Meteoritic `fossils' ● Future?

39. Venus ● Closest to Earth ● ¾ as far away from Sun as Earth is ● Very similar to Earth's size, density ● Covered by thick, opaque clouds

40. Reading for Next Class (Apr 16) ● Chapter 15: The Outer Solar Systen – History of Outer Solar System Exploration – The Nature of Gas Giants ● Atmosphere ● Chemistry – The Moons of Jupiter, Saturn, Uranus, Neptune ● Chapter 16: How Unique is Earth? – Necessary Resources – On Having a Large Moon – Staying alive by accident