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Fate of Planetesimals

Fate of Planetesimals

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Fate of Planetesimals

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  1. Fate of Planetesimals • Ejection from Sol. Sys. • Collision with planets • Capture as satellites, or into resonant orbits (e.g., the Trojan asteroids) • Fragmentation • Preservation to today (however, not necessarily in “pristine” condition) • comets • asteroids • meteors

  2. Comets • “comet” from “kome” (Gr.), meaning “hair” being descriptive of comet tails • Comets have been seen since ancient times, often considered bad omens • 1577 – Brahe deduced that comets are farther than the Moon from lack of parallax (as Earth rotates) • 1704 – Edmond Halley uses Newton’s gravity to discover that comets move on long elliptical orbits: Comets seen in 146, 1531, 1607, and 1682 are the same [also records for 66 and 451], with Porb= 75 yrs – Halley predicted its return in 1758 Halley’s comet!

  3. Comet Ikeya Zhang

  4. Nature of Comets WHAT“dirty snowballs” WHERE • The Oort cloud – named after discoverer Jan Oort (Dutch), a swarm of “dormant” comets at ~50,000 AU • Long periods (using P2=a3, P ~ 105-107 yrs) • Since they travel at less than vesc from the solar system as theyapproach, comets are thought to be part of S.S., in contrast to interstellar wanderers

  5. The Oort Cloud

  6. Comet Hyakutake

  7. Comet Components • Nucleus: the “snowball”, of a few km in diam. • Coma: halo of gases enveloping the nucleus, about 106 km in diam. • Tails: can extend to over 1AU; directed away from Sun • Plasma tail – driven back by ionized solar wind • Dust tail – repelled by sunlight, like mini-solar sails

  8. Anatomy of a Comet

  9. Comet Holmes (2007)

  10. Tail Development

  11. Long-period comets have orbits a) the same as the orbits of short-period comets b) that are circular c) always in the ecliptic d) randomly oriented with respect to the ecliptic e) of low eccentricity Share Question

  12. Comet Close-up • Giotto, a European probe, obtained 1st close-up images of Halley’s comet during its 1986 passage • Peanut shaped 15 x 7 x 10 km • Jets of gas and dust

  13. Halley’s Comet

  14. Comet Hale-Bopp

  15. Chunks of Shoemaker-Levy 9

  16. Comet Impacts at Jupiter

  17. Stardust Mission