The Solar System

Radar image Visual-wavelength image Vesta

13-km-deep crater

Model

Elevation map

500 km

Elevation

Dactyl

Enhanced visual

+ infrared

Double asteroids are more common

than was once thought, reflecting a

history of collisions and

fragmentation. The asteroid Ida is

orbited by a moon Dactyl only

about 1.5 km in diameter.

Occasional collisions

among the asteroids release

fragments, and Jupiter’s gravity

scatters them into the inner solar

system as a continuous supply of

meteorites.

Ida

Meteorite from Vesta

2 in.

5 cm

30 km

C

0.4

0.3

0.2

0.1

0.06

0.04

Albedo

(reflected brightness)

Bright

Dark

0.8 1.0 1.2 1.4 1.6

Ultraviolet minus visual color index

Grayer Redder

M S

Common in

the inner

asteroid belt

Common in

the outer

asteroid belt

2

3

4

3a

Asteroids

that pass

near Earth can be

imaged by radar.

The asteroid

Toutatis is

revealed to be a

double object—

two objects

orbiting close to

each other or

actually in contact.

The large asteroid Vesta, as shown at right,

provides evidence that some asteroids once had

geological activity. No spacecraft has visited it, but its

spectrum resembles that of solidified lava. Images

made by the Hubble Space Telescope allow the

creation of a model of its shape. It has a huge crater at

its south pole. A family of small asteroids is evidently

composed of fragments from Vesta, and a certain class

of meteorites, spectroscopically identical to Vesta, are

believed to be fragments from the asteroid. The

meteorites appear to be solidified basalt.

Vesta appears to

have had internal

heat at some point in its

history, perhaps due to

the decay of radioactive

minerals. Lava flows

have covered at least

some of its surface.

Although asteroids would look gray to your eyes, they can

be classified according to their albedos (reflected brightness)

and spectroscopic colors. As shown at left, S-types are brighter

and tend to be reddish. They are the most common kind of asteroid

and appear to be the source of the most common chondrites.

M-type asteroids are not too dark but are also not very red. They

may be mostly iron-nickel alloys.

C-type asteroids are as dark as lumps of sooty coal and appear to

be carbonaceous.

NASA

NASA

Courtesy of Russell Kemton, New England Meteoritical

NASA