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Asteroids… Comets… Meteoroids Asteroids • Fragments of rock that orbit the sun. • More than 50,000 total • Orbit in elliptical paths • Most located in the Asteroid Belt – Between Mars and Jupiter – Others are closer to the sun and others are beyond Jupiter • The largest is Ceres, 1,000 km in diameter – Large enough so that gravity has made it round; first classified as an asteroid, now as a dwarf planet! Composition of Asteroids – Similar to inner planets rocky – Classified/Grouped according to their composition – 3 types of asteroids 1. Carbon – dark (common) 2. Silicate – like earth rocks 3. Iron/nickel – shiny/metallic (rarest) Near-Earth Asteroids “NEA” Asteroids whose orbits bring them close to earth. – More than 1,000 – Possible dangers to earth – Example: Meteor crater, Arizona 50 m asteroid 1 km crater 40,000 years ago • NASA has a congressional mandate to catalog all near-Earth objects. Object Name Close Approach Date CA Distance* (AU) CA Distance* (LD) Estimated Diameter** H (mag) Relative Velocity (km/s) 138127 (2000 EE14) 2015-Feb-27 0.1864 72.5 1.0 km - 2.3 km 17.1 20.25 90416 (2003 YK118) 2015-Feb-27 0.0782 30.4 530 m - 1.2 km 18.5 10.22 (2014 TA36) 2015-Feb-27 0.1520 59.1 190 m - 430 m 20.7 12.31 (2015 DP53) 2015-Feb-28 0.0510 19.8 36 m - 80 m 24.4 8.58 (2014 YS34) 2015-Feb-28 0.0978 38.1 180 m - 410 m 20.8 6.94 (2015 DN53) 2015-Mar-01 0.1024 39.8 28 m - 62 m 24.9 7.57 Comets • Small bodies of ice, rock , and cosmic dust that follow elliptical orbits around the sun. • Example: – Halley’s comet, 1986, next 2061 • Every 76 years. – Hale-Bopp, 1997, next 4385 Two parts • Body: – Core or nucleus: made of rock, metal or ice (dirty snowball). – Coma: spherical cloud of gas and dust surrounds core. • Tail: – Longer Tail = gas lit up by solar wind – Shorter Tail = dust reflecting visible sunlight • Comets reflect light from the sun (off coma and tail) • The solar wind blows the tail of the comets. • Therefore, the tail of a comet always points away from the streaming particles of the solar wind, or away from the sun. • Long period comets take more than 200 years to orbit. • Short period comets take less than 200 years to orbit the sun. Oort Cloud • Where most comets originate (come from) • A spherical cloud of dust and ice • Lies beyond Neptune’s orbit and the Kuiper belt, surrounds our solar system. • Contains billions of nuclei of comets • All in elliptical orbits around the sun; very slow orbits; it may take some of them a few million years to complete one orbit! Meteoroids Meteors • The smaller rocky, icy, or metallic bodies that move throughout the solar system. • Meteoroids that enter Earth’s atmosphere. – They compress the surrounding air quickly, heating it up intensely – Most burn up in the Earth’s mesosphere – Meteors are the bright streak of light caused by this. – Also called shooting stars – Many create a meteor shower When to look for meteor showers • Perseids…mid August….50-75/hr (perseids of 2015 below) • Leonids … Peak Nov. 12-13…15/hr • Geminids… peak Dec. 13-14 Meteorites • Millions of meteoroids enter Earth’s atmosphere each day (they can be very small). • Some do not burn up… very large to begin with • A meteoroid or any part of a meteoroid that hits the earth is a meteorite. • Most easily found in the Antarctic. • 3 types – Stony (like rocks on Earth) – Iron (metallic looking) – Stony-iron (rare)