Solar System Debris

Asteroids

Primal rocks that never clumped together to form a planet

Total mass of all asteroids is 1/10 the mass of the Moon

Largest asteroids are a few hundred km across

Orbit Sun

Classified according to reflectivity (albedo)

Bright S type (silicate) 15%

Darker C type (carbonaceous)75%

Others 10%: mainly M type- large fractions of nickel and iron

Asteroid Properties

Most asteroids are too small to be resolved from Earth

Estimate size from amounts of light reflected and heat radiated

Stellar occultations also give size

C type asteroids are most primitive

4.6 billion years old

Have not undergone significant heating or chemical evolution since formation

Larger asteroids are roundish, small asteroids are irregular in shape

Asteroid Orbits

Most orbits are eccentric

Asteroid belt

Earth-crossing

Trojan asteroids

Asteroid Belt

Located between Mars and Jupiter

Most asteroids in solar system are in asteroid belt

First asteroid discovered was in belt:

Ceres (1801), largest, 940 km across

Inner asteroid belt dominated by S types (silicate)

Outer asteroid belt dominated by C types (carbonaceous)

Not enough mass in belt to make a planet

Earth-Crossing Asteroids

Orbits intersect Earth's orbit

Apollo asteroids, semi-major axes > 1 A.U.

Aten asteroids, semi-major axes < 1 A.U.

>1200 known

Asteroid Collisions with Earth

300 are considered dangerous

(size > 150 m)

Eventually asteroids will collide with Earth

Comet Structure

Nucleus, coma, tail, hydrogen envelope

Fig. 14.8, (b) Halley's comet in 1986

Comet Tails

Tails appearance varies

Ion tail- straight, emission from ionized atoms and molecule

Dust tail- light reflects off microscopic dust particles

Dust tails are affected more strongly by Sun's gravity than in tails

Fig. 14.9

Behavior of Comet Tails

Solar wind creates tail

Fig. 14.10

Comet Orbits

Most short period comets come from Kuiper belt

Fig. 14.11

Comet Nucleus

Nucleus is a dirty snowball, Fig. 14.14

Probably loosely packed ice

Comet Breakup

Comet Shoemaker-Levy 9 Nucleus is a dirty snowball, Fig. 14.16

Probably loosely packed ice

Meteoroids

Meteoroid- piece of interplanetary material

Asteroid is a large meteoroid

Meteor- when meteoroid burns up in atmosphere

Meteorite- when a piece of a meteoroid survives to the planet surface

Fig. 14.18