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Astronomy 241: Foundations of Astrophysics I
17. Comets & KBOs
Comets
Comets are icy objects which fall into the inner solar system.
Warmed by the Sun, they may develop long tails.
At other times, a comet is an inert lump of ice & dust.
To S
un
Comet’s Motion
Comet Halley
Asteroids and comets to scale
Comet Nuclei
Deep Impact: the Nucleus of Tempel 1
Evidence of Cometary Ice
Tempel Alive With Light
Analysis of collision debris suggests Tempel formed ~ 30 AU from the Sun.
Comets and Meteor Showers
Comets shed dust, sand and gravel which slowly spread out as they move along the comet’s orbit.
Comet Encke
If the Earth encounters one of these trails, we get a meteor shower.
Meteor Showers
100 AU
5 AU
S
20,000 AU
Overview: Structure
Inner system: terrestrial planets, asteroids.
Outer system: giant planets and moons, “KBOs”.
Oort Cloud: comets.
Wikipedia: Kuiper Belt
Largest Known Kuiper Belt Objects (and Satellites)
KBO Orbits
Scattered: highly elliptical
Classical: outside Neptune’s orbit
Resonant: like Pluto’s orbit
Plan View of the Solar System
Pluto’s Orbit
Pluto is in a 3:2 resonance with Neptune. This is stable since Pluto avoids Neptune.
Pluto’s Orbit
Pluto’s orbit is highly tilted (inclination i = 17°) to the rest of the solar system.
Wikipedia: Pluto
Orbital Populations KBOs above this line cross
Neptune’s orbit
3:2
The Resonant KBOs
Resonant KBOs (plutinos) avoid Neptune’s influence.
Scattered KBOs which cross Neptune’s orbit are easily perturbed.
These scattered KBOs may become comets.
Pluto and Charon
Hubble Maps Pluto
Double planet; many small moons; possibly formed by giant impact (similar to Earth-Moon system).
• orbit ⇒ mass: MPluto = 0.002 ME
• density: ~ 2 g/cm3
• composition: 1/3rd rock, 2/3rd ice
• thin atmosphere: N2, CH4, CO
Pluto has probably differentiated;Charon is too small to melt itself.
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