Minor Bits of the Solar System Asteroids Comets

Minor Bits of the Solar System Asteroids, Comets and Meteoroids & Extrasolar Planets too! Nucleus of Comet Wild 2

ASTEROIDS: aka, Minor Planets • Smaller than planets, but many similarities • Over 75, 000 cataloged; over 200, 000 down to 100 m “known”; lots discovered by Sloan Digital Sky Survey • Most are probably solid; irregular shape • Some are “rubble piles”, easily disrupted • Gaspra (S type) and Ida (S type, w/ “moon” Dactyl)

Asteroid Orbits • Most in ASTEROID BELT: 2. 1 AU < a < 3. 3 AU • Kirkwood gaps: PA = 1/2, 1/3, 1/4, 2/5, 3/7 PJ --- Jupiter prevented growth of a planet in the belt • Amor: Mars-crossing; Trojan: near Jupiter's L 4 and L 5 • Apollo: Earth-crossing, can big craters & destruction

Kirkwood Gaps: Resonances with Jupiter

Last Pop Quiz • Person at the right of each row, take out a piece of paper • Neatly print your name on it. • Pass it to your left. • If you’re here, 10 pt, if not, 0.

Answers to Review Questions 1. 2. 3. 4. 5. 6. 7. 8. T: Venus’s atm conducts heat rapidly F: Valles Marinaris & Olympus Mons (but it’s inactive) F: MJ = 318 ME but > 2 times all others! F: Saturn rotates almost as fast as Jupiter and has differential rotation too F: only after Uranus’s orbit wasn’t explained by known planets’ gravity was Neptune predicted, searched for & found T: 1: 2: 4 periods for Io, Europa & Ganymede heat Io & Europa a lot via elliptical orbits & induced strong tides T: Saturn has 61 known moons, but only Titan is big F: ion tails point away from Sun

Rest of Answers • 9) A -- iron rust gives Mars its red color • 10) E -- densities between 1. 3 and 2 g/cm 3 : ice+rock • 11) C -- 1/D = 1/R - 1/P here R=2. 00 d, P = 8. 00 d so 1/D = 1/2 - 1/8 = 3/8 and D = 8/3 d = 2. 67 d • 12) C -- rocky core, liquid metallic H 2, liquid & gas H 2 • 13) C -- 4 km/s and eventually escapes Vth=(3 k. T/mmole)1/2 (and Vesc = (2 GM/R)1/2 ) Vth(H 2)/Vth(O 2) = (m. O/m. H)1/2 = (32/2)1/2 = 4 and as Vth(O 2) = 1 km/s, Vth(H 2) = 4 km/s • Since Vth(H 2) > (1/6) Vesc = 2 km/s the H 2 will eventually escape

Asteroid Classes and Physical Properties • C-type (Carbonaceous): majority, darkest, dominate farther out, 1. 3 g/cm 3, porous? • S-type (silicate) reflect more light, more in inner belt, 2. 0 g/cm 3 • Biggest in the Asteroid Belt: Ceres (D = 940 km), Pallas (580 km), Vesta (540 km)--probably had volcanoes • Some are binary: from Earth --- Pallas, from Space (Galileo) --- Ida (& Dactyl); frequent collisions moons • New are Quaoar: past Pluto at 42 AU, (D = 1300 km), the 3 rd biggest Plutino -- very icy so really more like comets • Sedna: very eccentric, a 480 AU, D 1800 km -currently at 75 AU, most distant Kuiper belt object known

Space Mission to Asteroids Near Earth Asteroid Rendezvous: NEAR • Took close-up photos of Mathilde (C-type; about 60 x 50 km) in 1997 • Orbited and crashlanded into Eros (S -type; 34 x 11 km) in 2001. Inset: “young” area where rubble filled in craters

Danger from Space!!! Manicouagan reservoir in Quebec: 70 km in diameter: hit by meteoroid ~2 x 108 yr ago • When earth crossing asteroids hit the earth, the energy of the impact can be huge; speeds ~ 20 km/s • Even modest (100 m size) meteoroids can produce big craters (every 200, 000 yr or so) • Extinctions from massive amounts of debris kicked into the atmosphere, blocking sunlight for years and killing plants (every 70, 000 yrs or so) -- last one @ Cretaceous/Tertiary boundary 66, 000 yr ago

COMETS: Dirty Ice-balls Seen as bright trails across the sky COMPONENTS: • NUCLEUS --- typically 10 km across When warm enough the ice SUBLIMATES • COMA --- gases sublimated from nucleus • HYDROGEN ENVELOPE --- 106 km • IONIZED TAIL --- pushed directly away from the Sun, by the SOLAR WIND; up to an AU • DUST TAIL --- curved, due to inertia of heavier dust particles wanting to follow orbit

Cometary Structure (Halley)

Anatomy of a Comet Movie

Cometary Tails • Halley (last slide) • Giacobini-Zinner (1959); ion tail over 5 x 105 km • Hale-Bopp (1997) showed both ion and dust tails, streching over 40 O

COMETARY ORBITS • Very elliptical orbits, many highly inclined • Usually FROZEN; warm up near 5 AU • Most nuclei in OORT CLOUD: 10, 000 -- 50, 000 AU; originated closer, ejected by jovian planets long ago • “Short” period comets: KUIPER BELT --- formed outside Neptune: over 1000 known, so over 100, 000 > 100 km • Many molecules found in their spectra: CH 4, NH 3, CO 2 & H 2 O

Tail Directions and Density • Tails basically point away from the Sun, but dust tails form later and are more curved • As the comet recedes from Sun, its tail is in front of it! • VERY POROUS w/ ~ 0. 1 g/cm 3

Comet Deep-Freezers: The Oort Cloud and Kuiper Belt

Pluto: King of the Kuiper Belt Objects • Pluto isn’t much bigger than several other KBOs, especially Sedna, probably about the same size and Eris, which is probably somewhat bigger. • So Pluto should be called a Minor Planet (aka asteroid or KBO) not a (Major) Planet

Kuiper Belt Objects & Pluto • Eris, Pluto & other big KBOs • Pluto has 4 moons: Charon, Nix & Hydra • Surface in “true” color: made during eclipses of Pluto by Charon (and vice versa)

FAMOUS COMETS: Halley’s • In 1705 Edmund Halley recognized several historical apparitions as recurrent: 76 year period; calculated orbit • Predicted its return in 1758 --- confirmed Newton's Laws • As seen in 1910 (spectacular) and 1986 (much less so) • Vega 2 & Giotto flew by & came very close in 1986: showed it to be irregular (15 by 10 km), very dark, with jets streaming from cracked outer layers

Halley’s Comet’s Nucleus Resolved • Picture taken by ESA’s Giotto -- 50 m resolution. Brightest jets from gas and dust from nucleus

Hale-Bopp Nucleus Animation

FAMOUS COMETS: Shoemaker-Levy 9 • Discovered in 1993 while heading for Jupiter • Tides shredded and trapped it • Hit atmosphere in July 1994; big splashes above clouds • Effects in atm seen for months

Deep Impact Mission • Collision w/ Comet Tempel 1 on July 4 2005 • Impactor gouged out a large hole while main satellite used photography and spectroscopy to probe composition

METEOROIDS, METEORS, & METEORITES METEOROID: ANY DEBRIS < 100 m SIZE METEORS or Shooting Stars • Bright flashes in our atmosphere • Most: completely destroyed dust or pebbles • Rocks are brighter, some survive to become METEORITES

METEOR SHOWERS: many more than usual • bigger dust lost by a comet left in the same orbit for many years; comets eventually are worn out • when Earth crosses the tail, they appear to RADIATE from a constellation • Perseid on Aug 11, 50/hr (Swift-Tuttle) • Draconid on Oct 9, 500/hr (Giacobini-Zimmer) • Leonid on Nov 16, 10/hr (up to 1000/min) (Tuttle) • Brightest meteors from big independent Meteoroids

METEORITES: Messengers from Space Main CLASSES • STONY (93% of FALLS) --Most are S-type, basically rocky w/o chondrules, or achondritic -- these are the most common type to land. --Many are Carbonaceous --Rare & primitive: CARBONACEOUS CHONDRITES • STONY-IRON • IRON -- very rare, but easily recognized; so most commonly found type. • All have densities more like asteroids than comets

Big Meteorites Ahnighito, about 34 tons; Wabar, about 2 tons

Meteorite Types • Stony (silicate) showing a dark crust from melting during passage through atmosphere • Iron showing crystalline structure on polished and etched surface

Origins of Meteorites • Many left from Solar System formation: 4. 55 Gyr old • Primitive: mainly stony which condensed in inner SS and carbon rich ones that formed in outer asteroid belt) • Asteroid fragments --- show evidence of heating • Processed: from differentiated objects, some like lava flows, so from the surface; others metallic, so from the cores of smashed asteroids • Blasted off the Moon --- many inclusions (rare) • Ejected from Mars --- different abundances of trapped gases (really rare)

PLANETS AROUND OTHER STARS? • First evidence: DUST DISKS around nearby young stars. • Such disks often had holes in the center: likely to be areas cleared out by planets. • Spitzer ST of Fomalhut dust disk; Hubble ST of HR 4796 A

Resonably Direct Evidence • Only since 1994 (51 Pegasi) • Very accurate RADIAL VELOCITIES (50 m/s) of stars indicate tugs from much less massive objects with periods of days to years.

Doppler shifts show Extrasolar planets around 51 Pegasi & Upsilon Andromedae (3) • SECOND WAY: Very precise ASTROMETRY (0. 002 arcsec) could indicate wobbles in stars' paths over years which are also due to companions

Statistics of Extrasolar Planets As of 2009, > 400 good indirect planet detections Dozens of stars have multiple planets detected • Both techniques: Much easier to detect close, multi. Jupiter mass planets, so, most found are more massive than Jupiter but a few ~ Neptune have been estimated

Surprise: Hot Jupiters within 1 AU! Formed in situ; survive heat and wind? • Migrated inward through nebular disk? • Are these the typical planetary systems or just a selection effect? IS OUR SOLAR SYSTEM WEIRD? • A few planets transits have been seen after orbit known from radial velocity curves, confirming them for sure!

Other Searches for Extrasolar Planets Direct evidence preferred: we want an IMAGE! • Imaging via blocking out light of star: coronagraph (IR much better than visible since ratio less extreme) • Finally done in 2009 • Interferometry could separate very nearby points: Space Interferometry Mission being planned (~2012) • Next stage: Earths, not just Jupiters: • Kepler mission currently looking for transits (2009); found 1 • Giving info on atmospheres of jovian exoplanets • Search for Extra Terrestrial Intelligence (SETI): • How? : radio signals, optical (laser) signals, visits? ? ? • See Astronomy 1020 (Chapter 28)

Congratulations! • You’ve survived (well, only one exam’s left) Astronomy 1010.