Asteroids and Comets

1. Asteroids and Comets Clues to the origin of the Solar System

2. Asteroids • Rocky and metallic objects that orbit the Sun • Too small to be planets • Fragments of larger bodies and remnants from consolidation of SS • Main Asteroid Belt • Orbiting between Mars and Jupiter • Physics was thought to predict a planet should be in that orbit • Document the transition between terrestrial and gas rich planets • Evidence of a temperature gradient in the ancient solar nebula • Volatile poor inner belt • Volatile rich outer belt • Apollo or Near Earth Asteroids (NEA’s) • Smaller pop (~1% of total) • Highly elliptical orbits • May cross Earths orbit • Est. >1500 over 1km in diameter • 50million tons of new material to Earth and its atmosphere per year

3. Temperature profile of early Solar SystemRefractory vs Volatile

4. Asteroids (cont’d) • Trojans and Greeks are in Jupiter’s L4 L5 points • Lagrange Points • Hildas in 2:3 resonance w/Jupiter

5. Asteroids (cont’d) • Left-overs from the formation of the Solar System • Two theories of formation • Remains of planet destroyed by gravitational pull between Sun and Jupiter • Never accreted into planet for same reason • However, composition indicates that an object or objects of significant size to differentiate formed and were subsequently destroyed • Interest • Material from early formation of SS • Those of igneous composition can be radiometrically dated • 4.6by • Knowledge comes from debris falling to the Earth • Show us composition of SS based on location of formation • Record of planetesimals, formation, differentiation, break up

6. Meteorites • Distinct histories based on age, composition, internal structure, and size of bodies from which they originated • Stony – (92.8%) - silicate comp, hard to identify in field • Chondrites – (85.7%) - carbonaceous and enstatite • Ordinary – metamorphosed chondrites • Carbonaceous – carbon & volitile-rich, undifferentiated : similar to primative nebular material from which the planets formed (4.6by) • Achondrites - (7.1%) – igneous textures, differentiated : examples of primative crusts surrounding a differentiating planetoid • Some as young as 1.3by • SNC’s (Shergottites, Nakhlites, and Chassignites, see photo above) may be pieces of Martian crust • ~34 known

7. Mars crustal meteorite : Los Angeles Sample • Mojave Desert, Oct. 20th, 1999 • Basaltic shergottite • Note two-toned color • Fusion crust

8. Asteroids (cont’d) • Stony Iron – (1.5%) - silicate-metal mixture, differentiated • Quite rare • Pallasites – olivine crystals and Fe-Ni combination • Represent fragments of transition zone between metallic core and rocky mantle • Requires differentiation of larger asteroids (hundreds of km) • Iron (5%) • Fe and Ni composition • Easiest to identify • Widmanstatten figures • Evidence of originally molten material • Cooling history suggests these formed as core material of larger asteroids

9. Pallasites • Represent boundary btwn mantle and core • Large olivine crystals and Fe-Ni crystals • Note Widmanstatten pattern in sample above • Faceted space peridot crystal • This beautiful faceted gem came from an Esquel pallasite. It's rare to find such large, unshocked gem material outside the asteroid belt. 1.5 carat space peridot. The largest, cleanest stone ever recovered.

10. The Antarctic Connection • Many meteorites are found on the Antarctic ice sheet • First found by Japanese scientists in 1969 • Ice movement consolidates meteorites at terminus of glaciers • Easy to differentiate from surroundings • >16,000 samples found doubling our population for study • Martian, Lunar, Asteroids • Meteorites of composition compatible with nearby celestial bodies provide only samples we have (except Lunar rocks returned by Apollo missions)

11. 15-ton Willamette Meteorite discovered in Oregon • Known throughout local Native American oral lore • Composed mostly of Fe & Ni Largest ever found in U.S. & 6th in world • Probably well-traveled • No crater • Glacial erractic?

12. Sylacauga MeteoriteNovember 30, 1954 at 2:46pm Sylacauga, Ala. • No published photo • Often improperly called the Hodges Meteorite • First documented extraterrestrial object to have injured a human being • Grapefruit-sized fragment crashed through the roof of a frame house in Oak Grove, Alabama, bounced off a large wooden console radio, and hit Ann Elizabeth Hodges (1923-1972) who was napping on a couch • The 31 year old woman was badly bruised on one side of her body but able to walk • Not the only extraterrestrial object to have struck a human • 1992 a very small fragment (3g) of hit a young Ugandan boy but it had been slowed down by a tree and did not cause any injury

13. Asteroids (NEA’s) • NASA Near Earth Objects (NEO) utilizes observations of various entities to identify, monitor and plot potentially dangerous objects • Asteroids that approach or cross Earth’s orbit are known as NEA’s • ~2000 known NEA’s • Potentially Hazardous Asteroids (PHA’s) • Predicted bodies that may impact at some future time

14. Ceres • Smallest identified dwarf planet in the SS • Only one in the asteroid belt • Discovered 1 Jan. 1801, by Giuseppe Piazzi • For half a century it was classified as the eighth planet • Diameter of 950 km (590 mi) • Largest & most massive body in asteroid belt • Contains 32% of belt's total mass • Is spherical • Appears to be differentiated into a rocky core and ice mantle • May have an ocean of liquid water underneath its surface • On 27 Sept. 2007, NASA launched the Dawn space probe to explore Vesta (2011–2012) and Ceres (2015)

15. Asteroid Encounters • Galileo • Encountered Gaspra and Ida in flyby mode on way to Jupiter • NEAR (Eros) • In orbit for ~year • Landed on surface despite not a mission goal • Highest resolution images ever acquired • Deep Impact • Tempel Comet – designed to crash into comet • After traveling >3.5bm Feb. 14th, 2011 • 3 times around Sun Impact

16. Impact Craters • Record of early Solar System environment • Size and number indicative of age of surface • Mercury, Moon • Lack recent active geologic processes • Provide measuring stick for cratering throughout age of Solar System • Earth • 160 terrestrial impacts known • Previous covered by erosion or destroyed by plate tectonics • Meteor Crater (Barringer Crater) – Arizona • ~1200m diameter • ~50,000ya • Destruction radius > 30km • Chicxulub Crater – Yucatan Peninsula Mexico • 170km diameter • 64.98my • K-T boundary • Extinction of >70% of life forms • Iridium

17. Comets Harbingers of ill omen

18. Comets • Most primordial material from formation of outer proto-solar nebula • If SS cooled from out to in then material would not have changed much over time • Direct condensation of solar nebula • Impactors during early SS • Provided volatiles to inner planets • Water on Earth? • Origin of organic molecules • Building blocks of life?

19. Comet Components • Composed of ices and dusts • Coma • Nucleus or compacted body of comet • Icy dirtball w/carbonaceous material • 20% of surface is active • Tails • 2 tails • Visible larger • Volatiles being sublimated by solar energy • Dust reflecting sunlight • Invisible (bluish) smaller • CO2, H2O • Begins around Mars orbit • Always points away from Sun • Can be >10’s of millions of km in length • Material in most meteor showers • Next one : Lyrids nights of April 21/22 Sets around 3-4 a.m.

20. Comets • Kuiper Belt • Close to Pluto • Short orbital periods • Orbits are in same plane as SS • Oort Cloud • No direct evidence for cloud • Highly elliptical orbits • Vary from SS plane • May extend 200,000 times 1AU (1/10th distance to nearest star)

21. CometsShoemaker-Levy • Discovered in 1993 • Captured by Jupiter’s gravitational pull • Ripped into “string of pearls” • from July 16-22 collided with Jupiter in the first observed large impact within our SS • Bright explosive plumes easily visible with amateur telescopes • Larger than Earth • Light from Jupiter increased fifty-fold

22. Shoemaker-Levy • Image of Jupiter taken on the NASA Infrared Telescope Facility, Mauna Kea, Hawaii, at 08:54 on July 21, 1994 • Image taken using the IRTF's facility near infrared camera • Io, the closest of the jovian moons, can be seen crossing the planet (top right) • The Great Red Spot is visible in the lower left • At the collision latitudes, the impact due to Fragment Q is just setting on the west. Just to the east of it, the R Fragment impact site shows up very brightly. Another four impact sites form a chain of spots behind R

23. Shoemaker-Levy • The G impact site is visible as a complex pattern of circles seen in the lower left of the partial planet image. The small dark feature to the left of the pattern of circles is the impact site of fragment D. The dark, sharp ring at the site of the fragment G impact is 80% of the size of the Earth • Comet Shoemaker-Levy 9 broke up into 21 fragments during a close passage by Jupiter in July of 1992. Fragment G was one of the brightest and likely the largest of the 21 fragments • Scientists estimate that the combined energy from all of the impacts will approach the equivalent of 40 million megatons of TNT.

24. Shoemaker-Levy • Image of Jupiter with the Hubble Space Telescope Planetary Camera • Eight impact sites are visible. From left to right are the E/F complex (barely visible on the edge of the planet), the star-shaped H site, the impact sites for tiny N, Q1, small Q2, and R, and on the far right limb the D/G complex. The D/G complex also shows extended haze at the edge of the planet • The features are rapidly evolving on timescales of days The smallest features in this image are less than 200 kilometers across.

25. Eros • High resolution images of Eros as acquired by NEAR Shoemaker while in orbit around the asteroid • And as it landed

26. Carancas Meteorite and Crater • Chondritic meteorite • September 15, 2007, • Near the village of Carancas in Peru, close to the Bolivian border and Lake Titicaca • The impact created a crater and scorched earth around its location • A local official said that “boiling water started coming out of the crater, and particles of rock and cinders were found nearby”, as “fetid, noxious” gases spewed from the crater

27. Tempel 1 • Deep Impact of Comet Tempel 1 • Flyby and impactor probe • Goal to acquire data on material from inside a comet by creating an artificial impact crater • Images of ejected material can be spectroscopically analyzed for composition

28. Stardust • Sampled Wild2 comet • Silica Aerogel – glass but @ 1% density • Tail material is “clumped” • Calcium Aluminum Inclusions • Some of oldest SS material found in asteroids • Need heat to form • Collectors • Sweep up material from inner and outer SS • Smaller grains = outer • Larger grains = inner

29. Asteroid ItokawaThe “Rubble Pile” • Earth-orbit-crossing asteroid Itokawa, • Imaged by Japanese-made Kayabusa spacecraft in November, 2005 • Lack of craters and bi-modal form suggest accretion

30. 4179 Toutatis/1989 AC • An Apollo, Mars-crossing asteroid with a chaotic orbit • Orbital period of nearly 4 yrs • Frequent close approaches to Earth • Current min possible dist of 0.006 AU (2.3 times as far as the Moon) • September 29, 2004 was particularly close, at 0.0104 AU (within 4 lunar distances) from Earth • Most recent close approach (at 0.0502 AU) happened on November 9, 2008

31. P/2010 A2 • Imaged by Hubble Jan. 2010 • Object appears to have tail • 140-meter nucleus offset from the tail center • No discernable gas in the tail • Object orbits in asteroid belt • Debris left from recent collision between two small asteroids • Collision likely occurred at over 15,000 kph • 5X speed of a rifle bullet • Liberated energy in excess of a nuclear bomb Credit: NASA, ESA, D. Jewitt (UCLA)

32. Ida and Dactyl • In main Asteroid Belt • 56x24x21km • Only known asteroid w/natural satellite • Imaged by Galileo spacecraft on Aug. 28th, 1993