Minor members of the Solar System Asteroids, Meteors, Comets Formation • We have already seen how the solar system formed • Some planetesimals were left over when the solar system formed • These became the asteroids, meteoroids and comets • Many of the asteroids are in the asteroid belt. • What is an asteroid belt like? Link The Asteroid Belt • The asteroid belt occurs in orbit between Mars and Jupiter • The combined left over mass was not quite large enough to form another planet, especially due to the large disruptive force of gravity from nearby Jupiter, with its great mass. • Had the left over mass been larger, we might have had another planet there Ida and Dactyl Asteroids • So, asteroids are remnants from the formation of the solar system • They are therefore 4.5 billion years old and when we find pieces of them they give us information about the origins of the solar system • That is why we send probes to comets and asteroids Eros Asteroids • Asteroids occur in 3 types – Stony – Iron – Stony-iron • These actually are parts of asteroids that differentiated as shown in the link below Meteoroids, meteors, meteorites Leonid Meteor • These are actually all the same thing • They are named differently depending on their location • Small asteroid pieces are meteoroids • When they fall towards earth, burning up, they are called meteors. We get some of these all the time • If they actually hit the surface, then they are meteorites Comets • Comets are icy remnants of the solar system, with a small hard nucleus core and the surrounding gaseous coma • They reside in two regions, the Oort cloud and the Kuiper Belt Hale-Bopp • They orbit the sun in long period elliptical orbits • They begin to heat and vaporize as they approach the sun, forming a tail. The tail always points away from the sun, being pushed there by solar wind and radiation pressure Meteor showers • Many comets are periodic, visiting the sun regularly • When comets go around the sun, they leave many small pieces in their orbital paths • When the earth intersects this comet debris, we get meteor showers – many small meteors giving us a great light show as they burn up – rarely touching the ground • We can predict when we get these since we cross these orbital paths periodically, like the Perseids every August • The complete breakup of comet Shoemaker-Levy 9 in 1994 produced this spectacular telescopic image below After colliding with Jupiter Collisions • This is worrisome since the earth periodically also gets hit by larger solar system remnants – asteroids or comets • The mass extinction at the end of the Mesozoic was probably due to an impact in the Yucatan • There is a small government program that searches for asteroids on collision paths with earth. • If a large one hits, it would be very bad for us Review • • • • • • How old are asteroids Where are most asteroids located Where do you find a meteorite? Where are comets located? Which way does the tail of a comet point? Why do metoer showers occur? How likely is a large collision? • The map below shows major impact sites around the world. There are many of them. Craters • Most craters have been weathered and are not visible anymore • But they give evidence that we have been visited many times by these fragments from space • And it has happened before • What if a collision sent new asteroids our way. Could this happen? The End?