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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. Comets.

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Fate of planetesimals
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


Comets
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!



Nature of comets
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




Comet components
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


Anatomy of a comet
Anatomy of a Comet




Share question

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


Comet close up
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


Halley s comet
Halley’s Comet






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