Exploring the Planets

Impact Features

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.

Northeast Quadrant of the Caloris Basin, Mercury

This image of the northeastern quadrant of the Caloris basin shows the smooth hills and domes between the inner and outer scarps and the well-developed radial system east of the outer scarp.

Tycho Crater, Moon

Three images of Tycho crater and its central peak, located at 43 S, 11 W, on the Moon. These pictures were produced by using different filtered images from the UV/visible camera on the Clementine spacecraft.

Earth

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.

Meteor Crater Topography

Meteor Crater in the Colorado Plateau, 73 km east of Flagstaff, Arizona.

Manicouagan Reservoir

Manicouagan Reservoir marks the site of an impact crater, 60 miles (100 km) wide, which, according to scientists, was formed 212 million years ago when a meteorite crashed into this area.

Mars

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.

Bacolor Crater, Mars

This view combines images taken during the period from September 2002 to October 2005 by the Thermal Emission Imaging System instrument on NASA's Mars Odyssey orbiter.

Asteroids

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.

Asteroid Mathilde

This image mosaic of asteroid 253 Mathilde is constructed from four images acquired by the NEAR spacecraft on June 27, 1997.

Planetary Satellites

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.

Impact on Europa

Impact on Europa recorded by the Galileo spacecraft.

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.

Jupiter

Comet Shoemaker-Levy 9 (formally designated D/1993 F2) was a comet that broke apart and collided with Jupiter in July 1994. Brown spots mark impact sites on Jupiter's southern hemisphere.