Space Debris

1. Space Debris

2. Topics • Pluto • Kuiper-Belt Objects • Comets • Meteoroids • Asteroids • Summary

3. Pluto Discovered by Clyde Tombaugh in 1930 Fig. 8-2, p. 164

4. Pluto Charon Fig. 8-6, p. 166

5. Kuiper-Belt Objects (KBOs) • Beyond the orbit of Neptune lies a belt of icy objects • Object sizes: ~ 10 – several 100 km • Belt thickness: ~ 10 A.U. • Some scientists think that Pluto is really a KBO rather than a planet

6. Fig. 8-8, p. 168

7. Comets • Naked Eye Comets • Almost every decade, a comet becomes bright enough to be visible to the unaided eye • Here is a picture of Halley’s comet, which appeared in 1986 Fig. 8-15, p. 173

8. Comet Hyakutake

9. Comets – II • Composition • When a comet approaches the Sun, material streams away from the head to form a tail • At the center of the head is the nucleus, which is thought to be akin to a “dirty snowball” • The rest of the head is called the coma • Many comets have two tails: • A dust tail • A gas tail

10. Comet Hale-Bopp, 1997 Fig. 8-11, p. 170

11. Comets – III • Origin • It is thought that trillions of tail-less comets inhabit a sphere, centered on the Sun, of radius about 50,000 A.U. • This sphere is called the Oort Cloud. • Gravitational interactions from the Galaxy or passing stars occasionally nudge comets into orbits that bring them close to the Sun. • Comets may also come from the Kuiper Belt.

12. Halley’s Comet • 1705 • Suggested that the comet that appeared in 1531, 1607 and 1682 was the same object and that it would return in 1758. • Indeed, on Christmas night 1758 the comet appeared, confirming Halley’s prediction based on Newton’s laws Fig. 8-14, p. 172

13. Giotto Halley’s Comet in Giotto’s Adoration of the Magi 1304

14. Comet Shoemaker-Levy 9 • Discovered in 1993 by • Eugene and Carolyn Shoemaker • David Levy • At the Mount Palomar Observatory • The Hubble Telescope revealed a fragmented comet

15. Collision with Jupiter • July 1994 • Over a period of about a week, fragment after fragment hit Jupiter • The largest piece released 6 million megatons of energy, equivalent to that released by ~ 100,000 of the largest hydrogen bombs! • If the Earth had been struck instead, almost all life would have been destroyed. Fig. 8-20, p. 175

16. Fig. 8-21a, p. 176

17. Meteoroids • Many objects some tens of meters across are orbiting in our Solar System. • When in space they are called meteoroids • Those that enter the atmosphere are called meteors • The remnants that reach the ground are called meteorites. • Every year, about 10,000 tons of space debris lands on the Earth’s surface.

18. The Leonids Meteor Shower Fig. 8-25, p. 178

19. The Barringer Crater Arizona Fig. 8-28, p. 179

20. Asteroids • Asteroids • Most asteroids orbit in a belt between Mars and Jupiter • Near-Earth Objects • Some, however, orbit far from the asteroid belt and have orbits that cross that of Earth. • These near-earth objects are a genuine threat to our planet. • Most are expected to hit us eventually

21. Giant Impacts • Cretaceous/Tertiary Extinction • There is abundant evidence that Earth has been struck repeatedly by huge objects, some of which have visited catastrophic damage to the ecosystem • 65 million years ago, all dinosaurs and about ¾ of all other species suddenly became extinct • Evidence suggests that the Cretaceous/Tertiary extinction was caused by (at least) one giant impact

22. Mass Extinctions p. 183

23. Cretaceous/Tertiary Boundary in Montana http://www.ucmp.berkeley.edu/mesozoic

24. Chicxulub p. 183

25. Summary • Kuiper-Belt Objects • ~ 10s to 100s km across, beyond orbit of Neptune • Comets • “Dirty snowballs” that inhabit the Oort Cloud and Kuiper Belt. Kicked sunwards from time to time • Meteoroids • Objects 10s of meters across • In atmosphere: meteors; on ground: meteorites • Asteroids • Minor planets, one of which may have wiped out dinosaurs 65 million years ago