3B Solar System Debris Asteroids, Comets, Meteors, Oh My!

3B Asteroids Asteroids are small, irregular, rocky bodies that orbit the sun Most are located between he orbits of Mars and Jupiter in the asteroid belt Some are located in the same orbit as Jupiter, but are separated by 60º - Trojans Some asteroids are in highly elliptical orbits that pass earth – Earth-crossing asteroids, Near-earth asteroids (NEAs), Near-earth objects (NEOs)

3B What do asteroids look like? Too small to be seen with the naked eye – need large telescopes Appear as streaks because of their motion Three fly-bys of asteroids: –Gaspra by Galileo in 1998 –Ida by Galileo in ???? –Mathilde by NEAR in 1999

3B What are asteroids made of? Asteroids are classified into a number of types according to their spectra (and hence their chemical composition) and albedo: albedo 1.C-type, includes more than 75% of known asteroids: –extremely dark (albedo 0.03) –approximately the same chemical composition as the Sun minus hydrogen, helium and other volatilesvolatiles 2.S-type, 17% –relatively bright (albedo ) –metallic nickel-iron mixed with iron- and magnesium- silicates 3.M-type, most of the rest –bright (albedo ) –pure nickel-iron 4.There are also a dozen or so other rare types

3B Asteroids How many are there? –Some 5000 with well-determined orbits –Probably >500,000 larger than 1 km How big are they? –Largest (Ceres) is 940 km in diameter –Three larger than 500 km –About a dozen larger than 250 km –Number increases rapidly with decreasing size Total mass of all asteroids ~ 5% of the moon

3B Eros

3B More Eros

3B Eros Landing

3B Comets Comets are small bodies of ice and dust that form tails as they near the sun. What way is this comet moving? Recall Kepler’s second law. Where do comets spend most of their time?

3B What are comets made of? When they are near the Sun and active, comets have several distinct parts: –nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids; –coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus; sublimed –hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen; –dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye; –ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.solar wind

3B Comet Parts

3B Where do comets live? Short period comets come from the Kuiper belt Long period comets from the Oort cloud

3B What happens when comets loose their tails? Meteor showers

3B Meteorites Three main types: Stony –Look like ordinary earth rocks at first glance. If you were to look closely, you would see that the outsides of the rocks look melted. Most meteorites (93%) striking the earth are stony Irons –These dark grey, metallic, and very dense meteorites are unlike any earth rocks that you have ever seen. Five percent of meteorites striking the earth are irons Stony-Irons –These meteorites have clumps of both iron and stone

3B Asteroid – Meteorite Connection Iron –similar to type M asteroids Stony Iron –like type S asteroids Stony –Chondrite by far the largest number of meteorites fall into this class; similar in composition to the mantles and crusts of the terrestrial planets –Carbonaceous Chondrite similar to type C asteroids – Achondrite similar to terrestrial basalts

3B Finding Meteorites Finds –Found on earth, often long after they landed –usually noticed because of their unusual appearance or their unusual location Falls –These meteorites are seen falling, making a fireball in the sky. By following the trail, the landing site and meteorite can be found. Most of these are stony meteorites Peekskill, NY 1994

3B Impacts What happens when a meteor hits the ground? –Usually nothing –Occasionally, large pieces make it to the ground and create impact craters

3B Impact craters

3B Impact Hazards No person has ever been killed by a meteorite hitting earth However, a large impact killed the dinosaurs A smaller impact in remote Russia in 1908 knocked down trees and could have caused severe damage in a populated area

3B Earth Sterilizing Impact Mass Extinction Impact Civilization Threatening Impact

3B Terrestrial Impact Frequency year century million yr. billion yr. ten thousand yr. 100 millionmillion10, Hiroshima Tunguska K/T TNT equivalent yield (MT) Global catastrophe Tsunami danger