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) (2000 EE14) 2015-Feb km km (2003 YK118) 2015-Feb m km (2014 TA36) 2015-Feb m m (2015 DP53) 2015-Feb m - 80 m (2014 YS34) 2015-Feb m m (2015 DN53) 2015-Mar m - 62 m

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 …15/hr Geminids… peak Dec

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)