Announcements

1. Announcements • Assignments were very good this week! • Let me know this week if you’re planning to do a presentation rather than a report

2. The Search • An overview of the Mars Rover Mission • Gas Giant Planets • Sketch of a Gas Giant • Who's who in the Outer Solar System • Formation of Gas Giants • Formation of GG moons • Tidal Forces • Visits to the Planets • How Unique is Earth?

3. The Mars Rovers • Identical pairs of rovers sent to opposite sides of Mars • Spirit and Opportunity • Each has a 12:20 `day' (sol) ; since on opposite sides of Mars, it is always day for one of the two • Primarily geology mission.

4. The Mars Rovers • Launched in June/July 2003 • 3 Stages: • Get off out Earth's surface • Get out out Earth's orbit • Head towards Mars

5. The Mars Rovers • Began landing in Jan 2004 • Entered atmosphere at 12,000 mph (Chicago -> San Francisco in 9 minutes) • Broke using heat shield, parachute. • Took pictures on decent to gauge horizontal velocity • Deployed airbags • Fired retro-rockets • Bounced a lot

6. The Mars Rovers • Once landed and stable, base unfurled • Rover, which was also folded up, unfurled

7. The Mars Rovers

8. The Mars Rovers • Four Science Goals: • Determine whether Life ever arose on Mars • Characterize the Climate of Mars • Characterize the Geology of Mars • Prepare for Human Exploration

9. The Mars Rovers • Search, characterize rocks & soils that hold clues to past water activity and geologic process • Determine distribution, composition of minerals, rocks, and soils surrounding the landing sites. • Perform "ground truth" of surface observations made by orbiters • Search for iron-containing minerals that indicate water • Geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life.

10. The Mars Rovers • Cameras • Panoramic Camera (Pancam) • Microscopic Imager (MI) • Engineering cameras: Hazcams and Navcams • Spectrometers • Miniature Thermal Emission Spectrometer (Mini-TES) • Mössbauer Spectrometer (MB) • Alpha Particle X-Ray Spectrometer (APXS) • Rock Abrasion Tool (RAT) • Magnet Array

11. Gas Giant Planets • Overview • Who's Who • Formation • Moons • Tidal Forces

12. Our Solar System • Almost all of mass of planets are in the 4 giant planets

13. The Giants • The Giants are sometimes all called `Jovian' planets after Jupiter • After more exploration showed their diversity, this term lost favor

14. The Giants • The giant planets inhabit the outer solar system (5-30 AU) • This means they get less energy from the Sun (4% - 0.1%) per area • Top of cloud cover of planets is very cold (-170oF --- 350oF)

15. The Giants • The giant planets can be weighed very accurately by measuring the speed of their moons. • Much heavier than Earth, but not so heavy considering their size • Densities 600 – 1600 kg/m3, compared with Earth's 5700 kg/m3 • Mostly made of gas/liquids?

16. The Birth of Giants • In outer solar system, cooler • Less evaporative stripping of volatile gasses • If sufficiently massive cores form, can keep even volatile gasses • These gasses will be representative of the very early solar system

17. The Birth of Giants • Since early solar system is largely composed of Hydrogen, so will gas giants • Rocky or Icy or Slushy core • High-hydrogen atmosphere has some similarities to atmosphere in Miller-Urey experiment • Can form lots of organics

18. The Birth of Giants • Large rotating liquid metal region means large magnetic field • Jupiter: Significant field extends out size of the Sun! • Can seriously effect nearby objects.

19. The Birth of Giants • Large mass -> high pressure, temperature at center • Temperature at center of Jupiter ~ 4 times surface of Sun! • Collapse from origin of planet still slowly continuing • Releases heat energy • These planets have a source of heat Jupiter in Infrared

20. The Birth of Giants • Gas giants emit more heat than they absorb from Sun • At earlier times, would have been much hotter • Moons, which are nearby, heated by their nearby planet • Many of these moons are large (planet-sized) • Moons might be interesting for life? Jupiter in Infrared

21. The Composition of Giants • Structure of gas giant atmospheres depends on mass of planet • Lower planet mass -> lower interior pressure -> may not be high-pressure enough to make hydrogen into a liquid metal. • Rock/Ice cores surrounded by Hydrogen/Helium gas

22. The Moons of Giants • Planets large enough that many moons were also formed • Many of them planet sized in their own right • Get heat from planet • Some (Io/Jupiter) effected by planets magnetic field • Atmosphere? (Titan, Saturn) • Water? (Europa, Jupiter)

23. The Moons of Giants • Formation: like planets around sun • Rotating body, disk forms • Moons generally along plane of rotation of planet

24. Tidal Forces • Tidal forces familiar from Earth • Not due simply to gravitational attraction (that would just move the whole body) but the difference in gravitational force across the body • Gravity: inverse square • Tidal forces: inverse cube • REALLY matters how close the object is

25. Rings • Most of the gas giants have rings • Jupiters are very small, probably transient, and made largely of dust • Too close to planet, tidal forces are strong enough to disrupt moons or prevent them from forming • Result is material scattered in orbit around planet

26. Visiting the outer Solar System • Pioneer • Voyager I/II • Galileo • Ulysses • Cassini-Huygens

27. Pioneer 10,11 • Launched in 1972 • Camera, equipment for measuring gas/magnetic fields in the solar system, radiation • Now ghost ships • Carry plaque in case ever discovered • Plaque designed by Carl Sagan

28. Voyager I/II • Launched in 1977 • Carry cameras, equipment for measuring gas/magnetic fields in the solar system • Now at 90 AU (8.4 billion miles) • Still send trickle of data • Will continue transmitting until ~2020 (not enough sunlight to power equipment)

29. Voyager I/II • Carries a golden record • Has needle, instructions on how to play it on cover • Contents assembled by Carl Sagan • Contains music, greetings in 55 langaguges, natural/atmospheric sounds, written greetings http://www.jpl.nasa.gov/flash/voyager_record/index.htm

30. Voyager I/II • Travelled past Jupiter, Saturn • Voyager II then flew by Uranus and Neptune; Voyager I stopped by Titan (largest moon of Saturn), trajectory then sent it out of plane of galaxy

31. Ulysses • Sent to examine magnetic field, radiation from Sun, esp. poles • Sent to Jupiter for slingshot out of plane of ecliptic • Also obtained magnetic field data from Jupiter

32. Galileo • Launched 1993 • Study Jupiter's atmosphere, satellites, magnetosphere for 2 years. • Made encounters with asteroids • Arrived at Jupiter, Dec 1995 • Significantly advanced our knowledge of the Galilean moons • At end of mission was burned up in Jupiter's atmosphere to avoid contaminating moons http://www.jpl.nasa.gov/videos/quicktime/galileo.qtl

33. Galileo • Took pictures of direct impact of comet into Jupiter in 1994

34. Cassini-Huygens • Will arrive at Saturn later this year (July) • Already taking pictures • Will send a probe (Huygens) to Titan

35. Planets of Interest • Where might life be? • Gas Giants? • Moons? • Europa • Titan • Iapetus

36. Gas Giants • Convection is a fundamental process • Happens everywhere • Fluid heated at bottom rises, cools, falls back down • Gas giants have hot centers • Large-scale motions • Mix material

37. Gas Giants • Makes it difficult to imagine life forming • No real surface to live on • Chemicals constantly being mixed around • No originally contained environment (`protocell')

38. Moons • Gas giants have planet-sized moons • At least one (Titan) has a significant atmosphere • Another (Europa) very likely has liquid salty water under a layer of ice

39. Europa • Very suggestive it has a liquid underneath • No cratering • Many fractures, ridges on surface • What would this mean for life? • If some source of energy on inside (geothermal, chemical), very real possibility of some sort of life

40. Titan • Very Cold • Massive, Cold enough to have an atmosphere (1.5 x as dense as ours!) • No oxygen • No liquid water • Hydrogen rich • Interesting organic chemistry • Lakes of hydrocarbons? • Huygen probe 2005

41. Iapetus • Moon of mystery • Side facing away from Saturn is very, very dark • Much less light reflected than bright side • How did this happen? • What is the dark material?

42. How Unique is Earth? • What is special about Earth? • How important/rare are those things? • How many such planets are there likely to be?

43. Earth • Atmosphere • Large surface gravity • Reasonable temperature • Rocky srface • Large moon • Lots of heavy elements

44. How Important/Rare are these? • Heavy elements; • Likely ubiquitous in planets around Pop I stars

45. How Important/Rare are these? • Rocky Surface • Can happen if there is heavy elements (see above) • Probably true of all planets close enough to have liquid water • (But planet migration)

46. How Important/Rare are these? • Atmosphere • Requires not too close to sun • Requires massive enough planet

47. How Important/Rare are these? • Reasonable Temperature • `Goldilocks zone’ • Needs to be right distance to star

48. How Important/Rare are these? • So we require • Rocky Planet • Of the right mass • At the right distance from the star

49. Habitable Zone • Corresponds to further than Venus to about Mars distance for our Sun • Using inverse-square law, could calculate for other stars • Main requirement: liquid water in the presence of an atmosphere.

50. Habitable Zone: Binary Stars • About half of all stars are in binary systems • Stars orbit a common center of mass (more on that next week) • Can planets have reasonable orbits in such systems? • Yes, but must orbit one star or be far away from both; • `Figure 8’ orbits aren’t stable