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 – from lack of parallax (as Earth rotates), Brahe deduced that comets are farther than the Moon
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 successfully predicted its return in 1758
Halley’s comet!

3. Comet Ikeya Zhang

4. Comet Lovejoy

5. 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, so P ~ yrs)
Since they travel at less than vesc from the solar system as they approach, comets are thought to be part of the Sol. Sys., in contrast to interstellar wanderers

6. The Oort Cloud

7. Example of a long-period comet out of the ecliptic
Comet Hyakutake
Example of a long-period comet out of the ecliptic

8. Comet Components
Nucleus: the “snowball” core of a comet, 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, a pressure induced by photon momentum

9. Anatomy of a Comet

10. Comet Holmes (2007)

11. Tail Development

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. Model for comet tumbling and gas jets
Comet Hale-Bopp
Hale-Bopp from 1997 passage
Model for comet tumbling and gas jets

16. Chunks of Shoemaker-Levy 9

17. Comet Impacts at Jupiter

19. Comet Ison (2013)
Comet Ison enters from lower right, is disrupted during close
passage of Sun, and emerges at upper right (time lapse picture).

20. Sun Grazing Comets
Sungrazing comets are fairly common. These were discovered by the SOHO satellite that constantly stares at the Sun.

21. Stardust Mission

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

23. Oumuamua interstellar interloper

24. ‘Oumuamua interstellar interloper
Approached within 0.22 AU
of Sun in Sep 2017
About 230 x 35 meters
Has a tumbling rotation
Lacked a cometary tail, so is
likely metal-rich