The Solar System

Impact Cratering

NASA

NASA

NASA

Tycho

Euler

Rays

Tycho

Rays

Visual-wavelength imageVisual-wavelength image

VisualVisual

Visual

A meteorite

approaches the

lunar surface at high

velocity.

On impact, the

meteorite is

deformed, heated,

and vaporized.

The resulting

explosion blasts out

a round crater.

Slumping produces

terraces in crater walls,

and rebound can raise

a central peak.

1

1a

The craters that cover the moon and many other bodies in

the solar system were produced by the high-speed impact of

meteorites of all sizes. Meteorites striking the moon travel 10 to 70

km/s and can hit with the energy of many nuclear bombs.

A meteorite striking the moon’s surface can deliver tremendous

energy and can produce an impact crater 10 or more times larger in

diameter than the meteorite. The vertical scale is exaggerated at

right for clarity.

1b Rock ejected from distant impacts can fall back to the

surface and form smaller craters

calledsecondary craters. The

chain of craters here is a

45-km-long chain of secondary

craters produced by ejecta from

the large crater Copernicus 200

km out of the frame to the lower

right.

Bright ejecta blankets and rays

gradually darken as sunlight alters

minerals and small meteorites stir

the dusty surface. Bright rays are

signs of youth. Rays from the

crater Tycho, perhaps only 100

million years old, extend halfway

Rock ejected from distant

impacts can fall back to the

surface and form smaller craters

calledsecondary craters. The

chain of craters here is a

45-km-long chain of secondary

craters produced by ejecta from

the large crater Copernicus 200

km out of the frame to the lower

right.

Bright ejecta blankets and rays

gradually darken as sunlight alters

minerals and small meteorites stir

the dusty surface. Bright rays are

signs of youth. Rays from the

crater Tycho, perhaps only 100

million years old, extend halfway

around the moon.

Lunar craters such as Euler,

27 km (17 mi) in diameter, look

deep when you see them near the

terminator where shadows are long,

but a typical crater is only a fifth to a

tenth as deep as its diameter, and

large craters are even shallower.

Because craters are formed by

shock waves rushing outward, by the

rebound of the rock, and by the

expansion of hot vapors, craters are

almost always round, even when the

meteorite strikes at a steep angle.

Debris blasted out of a crater is

calledejecta, and it falls back to

blanket the surface around the crater.

Ejecta shot out along specific

directions can form bright rays.

Lunar craters such as Euler,

27 km (17 mi) in diameter, look

deep when you see them near the

terminator where shadows are long,

but a typical crater is only a fifth to a

tenth as deep as its diameter, and

large craters are even shallower.

Because craters are formed by

shock waves rushing outward, by the

rebound of the rock, and by the

expansion of hot vapors, craters are

almost always round, even when the

meteorite strikes at a steep angle.

Debris blasted out of a crater is

calledejecta, and it falls back to

blanket the surface around the crater.

Ejecta shot out along specific

directions can form bright rays.