|Craters are the most widespread landforms in the solar system. Craters are found on all of the terrestrial planets - Mercury, Venus, Earth and Mars. The surfaces of asteroids and the rocky, ice covered moons of the outer gas planets are cratered as well. The craters left by impacting objects can reveal information about the age of a planet's surface and the nature and composition of the planet's surface at the time the crater was formed.|
Mercury and The Moon
Impact craters dominate the surfaces of Mercury and the Earth's Moon. Both bodies lack liquid water on their surfaces that would erode impact craters over time. They also lack an atmosphere which, on planets like the Earth and Venus, could disintegrate meteoroids before they impact the surface. However, old craters can be eroded by new impact events. Mercury and the Moon have very old surfaces. One of the youngest large craters on the Moon is Tycho, which was formed about 109 million years ago.
|Mercury's Caloris Basin||
Tycho Crater, Moon
Clementine Image courtesy U.S. Geological Survey
The circular Caloris Basin, the largest feature found on the surface of Mercury, is believed to be a huge impact crater. Numerous craters have since been formed within the basin. In this image taken by Mariner 10, only half of the basin is visible.
|Liquid water, wind and other erosional forces erase impact craters on the Earth. There are still many craters on Earth which are visible from space. Some craters in areas of low rainfall (i.e. where little erosion occurs) are relatively intact, such as this crater - Meteor Crater in Arizona, U.S.A.|
|Manicouagan Crater, CANADA
NASA Space Shuttle Photograph
|Mars has experienced significant bombardment. The southern
hemisphere is more heavily cratered than the northern hemisphere. Winds
are the main erosional force on Mars and windblown dust and soil erode
craters over time. The structure of some Martian impact craters, such
as the one pictured here at left, provide evidence that suggests the
presence of water or ice in the surface at the time the impact occurred.
More about Martian craters.
Mars Global Surveyor Image from Malin Space Science Center
|Asteroids are rocky and usually heavily cratered due to a long history of impacts with other asteroids and possibly comets. Old impact craters on asteroids have beem deformed and erased by newer impact craters. Alternatively, impact events can disintegrate asteroids into smaller pieces. This asteroid, Mathilde, is interesting because of the large size of the impact craters on its surface. Despite the obvious intensity of the impacts, the asteroid was not destroyed. Scientists believe the asteroid must be uncommonly dense to have withstood such bombardment.||
Europa Impact Feature
The outer gas planets do not have solid surfaces, but their moons do. Most of these moons are rocky, icy worlds with a variety of surface features and compositions. Most of them are cratered, such as Europa, one of the Galilean satellites of Jupiter. Europa's surface is thought to consist of a thick layer of ice overlaying a liquid water ocean.
Image from NASA/JPL Planetary Photojournal
Impact with Jupiter
|Comet Shoemaker-Levy Impacts with Jupiter
Terrestrial planets aren't the only ones that are hit by meteors, comets and asteroids. The planets known as gas giants, such as Jupiter, don't have a solid surface to keep a record of impacts. However, the impact of comet Shoemaker-Levy in 1993 left visible holes in the cloudtops of Jupiter. The effects of these holes began to fade after only a few months, but it was the first time humans observed a major collision between two objects in our solar system.
Exploring The Planets
©2002 National Air and Space Museum