Astronomy 241: Foundations of Astrophysics I 17. Comets & KBOs Comets To Sun Comet’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 Tempel 1 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 shower. Meteor Showers Comet Encke Overview: Structure 100 AU S 20,000 AU 5 AU Inner system: Outer system: Oort Cloud: terrestrial planets, giant planets and comets. asteroids. 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..