Meteoroids often break apart into fragments when they pass through planetary atmospheres. When those fragments impact the surface of planets, they form a group of craters called a crater cluster. The distribution of those craters depends not only on the properties of the meteoroid but also on atmospheric density. Because atmospheric density near the surface of Mars primarily depends on the elevation of the surface, scientists such as Ingrid Daubar from Brown University have hypothesized that distributions of craters in martian crater clusters should, in some way, depend on elevation.
Expanding on a prior study of 77 crater clusters by Daubar, Tanja Neidhart and Eleanor Sansom from Curtin University and colleagues (including Daubar) examined 557 crater clusters formed on Mars within the last 20 years. A variety of parameters were calculated for each crater cluster, including the effective diameter of an equivalent single crater, which can be used as a proxy for the volume of an average meteoroid fragment that formed the cluster. Neidhart, Sansom, and colleagues found that larger diameters of the largest crater in the cluster were strongly correlated with larger effective diameters. Larger effective diameters were also correlated with greater numbers of craters in the cluster, increased numbers of small craters relative to large ones, and increased spatial dispersion of the craters. Crater clusters at higher elevations had larger effective diameters and increased numbers of small craters. However, no correlation was found between elevation and crater count, and increased elevation was correlated with decreased dispersion. Based on their data, Neidhart, Sansom, and colleagues conclude that impacts at higher elevations were more energetic and that the atmosphere tends to disperse meteoroid fragments and ablate small fragments. However, whether a single crater or crater cluster is formed, as well as the crater count in any given cluster, seems to be determined primarily by the material properties of the meteoroid. READ MORE