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Astronomy 340 Fall 2007

This document outlines essential announcements for the Astronomy 340 course, including the final exam schedule set for Tuesday, December 18, at 10:50 AM in room 6515, and the due dates for Homework #6 and the project. Students are encouraged to attempt homework for practice, as grading will consider a class curve. It also highlights important topics for review, such as the atmospheres and interiors of giant planets, satellites of outer planets, rings, comets, dwarf planets, and detection techniques for extrasolar planets.

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Astronomy 340 Fall 2007

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  1. Astronomy 340Fall 2007 11 December 2007 Class #29

  2. Announcements • Final Exam - Tues Dec 18 at 10:50am in 6515 • HW#6 due Thursday in class • You will not be penalized for not doing the HW (though I do recommend you try them!) – points will be award after dealing with the class curve • Project due on Thurs Dec 13

  3. Second Half Review • Atmospheres of giant planets – know the basic compositions and we’ve figured that out • Interiors of the giant planets • Chapter 6.1 (eqn 6.27) • Figure from page 24 of Lecture 18 (Fig 6.23) • What are the J terms all about? • What is the underlying physics behind the derivation of the maximum size of a planet • Satellites of the outer planets • Figure 6.21

  4. Second Half Review – cont’d • Satellites of the outer planets • Chapters 5.5.5, 5.5.6, 5.5.7, 5.5.8, 5.5.9 • Know why Io, Europa, Titan, Encelaedus, Triton are interesting – what’s the role of tidal forces in all this? • Lecture 20 & 21!!! • Rings – what accounts for the variation in structure? • Chapter 11 (through 11.4) • Comets – equation 10.5 • Chapter 10.3, 10.6, 10.7

  5. Second Half Review – cont’d • Dwarf Planets and KBOs • You should be able to summarize the results of your project • How do you estimate the mass/size of a KBO? • Why is Pluto considered a dwarf planet? • What are the advantages of near-IR spectroscopy? • Recreate the HW question on why asteroids are brighter in the mid-IR than in the optical – do you think the same is true for KBOs? • Extrasolar Planets • Detection techniques (how do they work and what are the limitations?) • Chapter 13 • Star/Planet Formation • Chapter 12 • Eqn 12.7, 12.22 • What are the effects of planetary migration and why do people think it happens?

  6. Review • What are the primary techniques for detecting extrasolar planets and how do they work? • Given the radial velocity curve for a star would you be able to identify the period, mass, orbital eccentricity of the orbiting planet? • How do you detect atmospheres around exoplanets?

  7. Fraction of Stars with Planets Lineweather & Grether

  8. Star Formation

  9. Star Formation Feigelson & Montmerle

  10. Star Formation

  11. Key Observations of the Solar System • Coplanar/prograde orbits – angular momentum • Orbital spacing • Comets • 0.2% of mass in planets, 98% of the angular momentum • composition • Asteroid belt  power law size distribution • Age  4.5Gyr • Consistent isotopic ratios • Rapid heating/cooling • Cratering record  bombardment

  12. Key Physical Characteristics • Angular momentum  disk formation a must • Key properties of disk • Same abundance as the star • Spins in the same direction as the star • Temperature/density gradient (T(r) ~ r-0.5) • Other characteristics • Size: 25-500 AU observed • Total mass ~ 0.04 MEarth • R ~ 150 AU • Lifetime: 105-107 years

  13. 1st Phase - Condensation • Grains can survive in ISM conditions • Condensation • Nebula/disk cools  solids condense • “refractory” elements go 1st • Fe, silicates condense at 1400-1700 K • Meteoritic ages  condensation ~4.5 Gyr ago • Meteorites sample asteroid belt

  14. 2nd Phase – Collisional Accretion • Sticky collisions • Vi = (V2 + Ve2)1/2 = impact velocity • Ve = [2G(M1+M2)/(R1+R2)]1/2 • If Vi < Ve bodies remain bound  accretion • Growth rate • dM/dt = ρvπR2Fg or R2ΣΩFg/(2π) • Fg = cross-section = 1+(Ve/V)2 • dR/dt = (ρdv/ρp)(1+[8πGρpRp2]/3v2) • ρd = mass density in disk • ρp = mass density of planetesimals • V = average relative velocity • Rp= radius of planetesimals

  15. Collisional Accretion continued • If Ve >> V, then dR/dt goes as R2 big things grow rapidly • Can evaluate growth rate using R1=R2 (same assumption for V) • Formation of rocky/solid cores  next step is accretion • Raccretion = GMp/c2 (c = speed of sound)

  16. Collisional Accretion III • Predicted timescales • Accretion of dust  1 km sized bodies (104 yrs) • “runaway growth”  1 km to planetesimals (105 yrs) • Impacts finalize terrestrial planets (~108 yrs) • Lifetimes • Disk lifetimes: 105-107 yrs so process must be complete by then! • Earth timescales ~ 108 yrs • Much larger for Neptune

  17. Formation Scenarios • Core Accretion vs Gravitational Collapse • Q = κc/πGΣ gravity vs thermal pressure • Surface mass density • Local velocity (dispersion, sound speed) • Κ = R-3(d/dr(R4Ω2)) • Timescales ~ freefall time • One simulation with Md ~ 0.1 Earth masses, T~100K, Rd~20 AU  make J in 6Myr • Benefit • Can make planets on eccentric orbits • Timescales are short • Minuses • Hard to explain rocky cores

  18. Core Accretion Alibert, Mordasini, Benz 2004

  19. Formation Issues • Minimum Mass  r—1.5 • Core-Accretion • Timescales too long for Uranus, Neptune • What makes cm-size things stick? • How come things don’t spiral into Sun? • Gravitational Collapse • Faster, but is it plausible?

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