EART160 Planetary Sciences

1. EART160 Planetary Sciences

2. Introductions

3. Course Overview • Foundation class for Planetary Sciences pathway • Introduction to formation and evolution of planetary bodies in this Solar System • Focus on surfaces, interiors and atmospheres of planetary bodies, especially solid ones

4. Course Outline • See syllabus.

5. Logistics • Website: http://people.ucsc.edu/~igarrick/EART160 • Optional text – Hartmann, Moons & Planets, 5th ed. • Prerequisites • One of: Math 11B or 19B; and • One of: Phys 6A or Phys 5A. • WARNING: I am going to assume a good working knowledge of single-variable calculus and freshman physics. You will need to be able to set up and solve “word problems”. Don’t be under any illusions – this is a quantitative course. • Grading – based on weekly homeworks (25%), midterm (25%), term paper (25%), final (25%). • Homeworks generally due on Thursdays • Plagiarism – see Syllabus for policy (posted on web) • Office hours – Tuesdays 9-10 am, 5-7 pm (A137 E&MS) or by appointment (email: igarrick@ucsc.edu) • TA: Sarah Neuhaus, suneuhau@ucsc.edu • Questions? - Yes please!

6. Expectations • Homework typically consists of 3 questions • If it’s taking you more than 1 hour per question on average come and see me • Late homework penalized by 10% per day • Midterm/finals consist of short (compulsory) and long (pick from a list) questions • Showing up and asking questions are usually routes to a good grade

7. Summer Research Opportunities • There are a number of programs, usually paid, for summer undergraduate research positions in planetary science • I will put a list of some of these programs on the class website http://people.ucsc.edu/~igarrick/EART160

8. Next two classes • Introductory stuff • Highlights • Formation of the solar system and planets: • What is the Solar System made of? • How and how fast did the planets form? • How have they evolved subsequently? • [How typical is our Solar System?] Don’t hesitate to ask questions – it’s what I’m here for

9. Apollo: the birth of planetary science

10. Highlights (1) 2. Itokawa 1. The surface of Titan What is the fluid? Sample return.

11. Highlights (2) 3. Subsurface oceans How do we know?

12. 250 km diameter Highlights (3) 4. Enceladus geysers 5. Direct imaging of exoplanets What is the energy source? Any Earths out there? HR8799

13. Extrasolar planets • Sun-like star Gliese 370 and its “Goldilocks” planet 85512b. • 3.6 times as massive as the Earth. • 36 light-years away, in the constellation Vela. • How do we know if it supports water?

14. Selected Missions

15. Mission Highlights Chandrayaan-1 (India) Moon Kaguya (Japan) Mercury, the last unknown (MESSENGER) Chang’e (China)

16. Mission Highlights GRAIL Other lunar missions Chandrayaan 2 Chang’e-3

17. LADEE

18. Mars Science Laboratory

19. Kepler (2009-2013) • 0.3 percent sky field of view. Transit method. • > 100 confirmed exoplanets, >3000 unconfirmed. • By inference, 17 billion Earth-sized planets in the galaxy (2 billion habitable). • 1021 in the universe. • $550 million 95 Mpixels

20. NASA budget, the James Webb Telescope, and the future of robotic exploration. James Webb - $8B Titan mare explorer, ~$500M Micro Moon Impactors, ~$25M

21. What I work on

22. Lunar samples

23. Lunar swirls

24. Low cost missions

25. Lunar cubesat impactor for Planetary Hitchhiker TDM Cubesat data are transmitted to mother ship up until impact, yielding data from < 100 meters altitude. A new kind of near-surface lunar science, infused into an OCT TDM mission. Berkeley CINEMA cubesat

26. CINEMA (Cubesat for Ions, Neutrals, Electrons, & MAgnetic fields)UC Berkeley, NSF-funded, planned launch August 2012 Collaboration w/Kyung Hee Univ. Korean World-Class-Univ. (WCU) program - build & launch 2 more CINEMAs for stereo ENA (Energetic Neutral Atom) imaging & multipoint in situ ion/electron measurements

27. CINEMA 1 & P-POD NSF funding one unit, Air Force funding two more units. Kyung Hee University (Korea) building two more. Measures: 1) Magnetic fields and 2) Particle fluxes. Scheduled launch September 2012 http://sprg.ssl.berkeley.edu/cinema/

28. NPSCuL Integration

29. Assembled STEIN Flight Instrument CINEMA instruments 1 m boom magnetometer STEIN 32-pixel detector & ASIC electronics

30. What does the Solar System consist of? • The Sun is 99.85% of the mass (78% H, 20% He) • Nine Eight Planets • Satellites • A bunch of other junk (comets, asteroids, Kuiper Belt Objects etc.)

31. Terrestrial planets Gas giants Ice giants V E Me Ma Inner solar system 30 AU Note log scales! 1.5 AU 5 AU Outer solar system Where is everything? Note logarithmic scales! Ma V E Me J S U KB N P 1 AU is the mean Sun-Earth distance = 150 million km Nearest star (Proxima Centauri) is 4.2 LY=265,000 AU

32. Basic data See e.g. Lodders and Fegley, Planetary Scientist’s Companion

33. Solar System Formation • The basic characteristics of this Solar System – composition, mass distribution, angular momentum distribution – are mainly determined by the manner in which the solar system originally formed • So to understand the subsequent evolution of the planets (and other objects), we need to understand how they formed

34. In the beginning . . . • Elements are generated by nucleosynthesis within stars • Heavier elements (up to Fe) are formed by fusion of lighter elements: H -> He -> C -> O • Elements beyond Fe are produced by nuclei absorbing neutrons • Elements are scattered during stellar explosions (supernovae) and form clouds of material (nebulae) ready to form the next generation of stars and planets Elemental abundance (log scale) From Albarede, Geochemistry: An introduction

35. Solar System Formation - Overview • Some event (e.g. nearby supernova) triggers gravitational collapse of a cloud (nebula) of dust and gas • As the nebula collapses, it forms a spinning disk (due to conservation of angular momentum) • The collapse releases gravitational energy, which heats the centre; this central hot portion forms a star • The outer, cooler particles suffer repeated collisions, building planet-sized bodies from dust grains (accretion) • Young stellar activity (T-Tauri phase) blows off any remaining gas and leaves an embryonic solar system • These argument suggest that the planets and the Sun should all have (more or less) the same composition • Comets and meteorites are important because they are relatively pristine remnants of the original nebula

36. a Jeans Collapse • A perturbation will cause the density to increase locally • Increased density -> increased gravity -> more material gets sucked in -> runaway process (Jeans collapse) Collapsing cloud Gravitational potential energy M,r R Thermal energy Equating these two and using M~rR3 we get: M=mass r=density k=Boltzmann’s constant m=atomic weight N=no. of atoms T=temperature (K) Does this make sense? Example: R=60 light years T=50 K gives rcrit~10-20 kg m-3 This is 6 atoms per c.c. (a few times the typical interstellar value)

37. Sequence of events • 1. Nebular disk formation • 2. Initial coagulation, orderly growth (~1-10km, ~104 yrs) • 3. Runaway growth (to Moon size, ~105 yrs) • 4. Oligarchic growth (to Mars size, ~106 yrs), gas loss (?) • 5. Late-stage collisions (~107-8 yrs)

38. Accretion timescales (1) • Consider a protoplanet moving through a planetesimal swarm. We have where v is the relative velocity and f is a factor which arises because the gravitational cross-sectional area exceeds the real c.s.a. f is the Safronov number: Planet density r vorb Where does this come from? R fR where ve is the escape velocity, G is the gravitational constant, r is the planet density. So: Planetesimal Swarm, density rs

39. Accretion timescales (2) • Two end-members: • 8GrR2 << v2 so dM/dt ~ R2 which means all bodies increase in radius at same rate – orderly growth • 8GrR2 >> v2 so dM/dt ~ R4 which means largest bodies grow fastest – runaway growth • So beyond some critical size (~10 km size), the largest bodies will grow fastest and accrete the bulk of the mass • Growth timescale increases with increasing distance (why?): Approximate timescales t to form an Earth-like planet. Here we are using f=10, r=5.5 g/cc. In practice, f will increase as R increases. Here s is the nebular density per unit area and n is 2p /orbital period. Note that forming Neptune is problematic!

40. Late-Stage Accretion • Once each planet has swept up debris out of the area where its gravity dominates that of the Sun (its feeding zone, or Hill sphere, = oligarchic growth), accretion slows down drastically • Size of planets at this point is determined by the radius of the Hill sphere and local nebular density, ~ Mars-size at 1 AU • Collisions now only occur because of mutual perturbations between planets, timescale ~107-8 yrs – planetary dynamics. Agnor et al. Icarus 1999

41. Nice model • Quicktime movie

42. Complications • 1) Timing of gas loss • Presence of gas tends to cause planets to spiral inwards, hence timing of gas loss is important • Since outer planets can accrete gas if large enough, the relative timescales of planetary growth and gas loss are important • 2) “Snow line” • More solid material is available beyond the snow line, which allows planets to grow more rapidly • 3) Jupiter formation • Jupiter is so massive that it significantly perturbs the nearby area e.g. it scattered so much material from the asteroid belt that a planet never formed there • It must have formed early, while the nebular gas was still present.

43. Timescale Summary Dust grains Orderly growth ~10 km (planetesimal) ~0.1 Myr Runaway growth, gravity becomes important. ~1 Myr ~Mars-size (embryo) Late-stage accretion, oligarchic growth. (Giant impacts. Gas loss?) ~Earth-size (planet) ~10-100 Myr – Formation of the Moon 100+ Myr – larger cratering events

44. How did the Moon form? • Why didn’t it fall back into the Earth? • Would we be here without a Moon? • Why does Venus rotate so slowly?

45. Last impacts – Topography of Mars

46. Giant Impact on Mars

47. Lunar impact South Pole Aitken basin

48. Motivation/Observations

49. An Artist’s Impression gas/dust nebula The young Sun solidplanetesimals

50. T-Tauri Star • ~10 My phase of stellar evolution before a star starts to burn hydrogen (main sequence star). • Anomalously bright due to: • Large surface area (still-collapsing) • Large release of gravitational energy • Blows away nebula gases very rapidly via intense stellar winds