Astronomy 241: Foundations of Astrophysics I

17. & KBOs

Comets To ’s Motion Comets are icy objects which fall into the inner solar system.

Comet Halley Warmed by the Sun, they may develop long tails.

At other times, a comet is an inert lump of ice & dust. Comet Nuclei

Asteroids and comets to scale Deep Impact: the Nucleus of

Evidence of Cometary Ice

Analysis of collision debris suggests Tempel formed ~ 30 AU from the Sun. Tempel Alive With Light Comets and Meteor Showers

Comets shed dust, sand and gravel which slowly spread out as they move along the comet’s orbit. If the Earth encounters one of these trails, we get a .

Meteor Showers

Comet Encke Overview: Structure

100 AU

S

20,000 AU 5 AU

Inner system: Outer system: : terrestrial planets, giant planets and comets. . moons, “KBOs”. Largest Known Kuiper Belt Objects (and Satellites)

Wikipedia: Kuiper Belt KBO Orbits

Classical: outside Neptune’s orbit

Resonant: like Pluto’s orbit

Scattered: highly elliptical

Plan View of the Solar System Pluto’s Orbit

Pluto’s orbit is highly tilted (inclination i = 17°) to the rest of the solar system.

Wikipedia: Pluto

Pluto is in a 3:2 resonance with Neptune. This is stable since Pluto avoids Neptune.

Pluto’s Orbit Orbital Populations KBOs above this line cross Neptune’s orbit

Resonant KBOs (plutinos) avoid Neptune’s influence. 3:2

Scattered KBOs which cross Neptune’s orbit are easily perturbed.

The Resonant KBOs

These scattered KBOs may become comets. Pluto and Charon

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; Hubble Maps Pluto Charon is too small to melt itself.