Impact crater map

We map craters by drawing their outlines and recording their morphology—their shapes and features. Knowing the numbers, sizes and distribution of craters helps us determine the age of surface rocks and reconstruct the history of the surface. You can try crater counting in the research activities!

The Amazonian period is named after the young, flat Amazonis Planitia, which has the fewest craters and is younger than three billion years. The Hesperian period is named after the volcanic lava surface of Hesperia Planum, formed about 3.5 billion years ago and now moderately cratered. The Noachian period is named after the densely cratered Noachis Terra highlands: the oldest surviving surface, about four billion years old. Materials from earlier times became mixed into younger layers. The first crust of Mars is 4.5 billion years old.

Stuart Robbins and Brian Hynek mapped the craters at the University of Colorado. Of the 600,000 surveyed craters, this map shows the 384,344 larger than one kilometre. The Moon has 1.3 million craters larger than one kilometre, also counted by Robbins and colleagues.

The mixed breccia meteorite Black Beauty contains material from different impacts. Its oldest mineral grains solidified when the last primordial crust of Mars cooled. Three impacts redistributed these grains: Dampier four billion years ago, Khujirt 1.5 billion years ago, and Karratha 5–10 million years ago (see map sheet 13). One of the ejected rocks travelled quietly and persistently around the Sun until its orbit intersected the Sahara (Lagain et al., 2022).

Impact breccia consists of mixed debris from the target rock; only a tiny part is material from the impactor, which vaporises. Some target fragments melt and solidify in flight into stretched, dough-like shapes called fladen. These mix with rock powder ground to ash-like fineness in the explosion, before everything falls back to the ground.

Some impacts eject surface rocks fast enough to leave Mars and eventually fall to Earth. A meteorite’s source crater can be sought by comparing the age of its breccia or lava and the time spent in space since the ejecting impact. If the age of a crater and its surrounding rocks agrees with these values, the source may have been found.

Shatter cones are characteristic rocks found in terrestrial impact craters. None have yet been seen in Martian or lunar photographs.