The morphology of small fresh craters on Mars and the Moon

Abstract

The depth/diameter ratio for new meter-to decameter-scale Martian craters formed in the last 20 years averages 0.23, only slightly deeper than that expected for simple primary craters on rocky surfaces. Large variations in depth/diameter (d/D) between impact sites indicate that differences between the sites such as target material properties, impact velocity, angle, and physical state of the bolide(s) are important in determining the depth of small craters in the strength regime. On the Moon, the d/D of random fresh small craters with similar diameters averages only 0.10, indicating that either the majority of them are unrecognized secondaries or some proportion are degraded primaries. Older craters such as these may be shallower due to erosional infilling, which is probably not linear over time but more effective over recently disturbed and steeper surfaces, processes that are not yet acting on the new Martian craters. Brand new meter-to decameter-scale craters such as the Martian ones studied here are statistically easily distinguishable as primaries, but the origins of older craters of the same size, such as the lunar ones in this study, are ambiguous.

Impact Ejecta Characterization for Small-Sized Fresh and Degraded Lunar Craters Using Radar Data

“…In the present study, we observed steeper slope (0.033) compared to Daubar et al 40 for small craters, and Pike 39 for large craters ( Figure 2). A deviation from 0.2 may result due to crater degradation, measurement errors arising due to small size of craters and target properties as indicated by Daubar et al 40 for small-sized craters. Our observations also present similar deviation from 0.2 as indicated by Daubar et al 40 for the 0.2-6 km size craters.…”

“…Further, variations in d/D can also reflect on the target material strength, impact velocity and impact angle, which play an important role in establishing the crater depth 40 . Earlier studies have suggested that the d/D ratio decreases with the passage of time due to continuous crater degradation and material infilling 41 .…”

Small crater modification on Meridiani Planum and implications for erosion rates and climate change on Mars

“…They are typically bowl shaped with a depth/diameter ratio of 0.2 and a rim height/diameter ratio of about 0.04 [ Pike , ; Melosh , ]. Small fresh lunar craters [ Basilevsky et al ., ] and a sample of several hundred small primary craters observed in before and after images (Context Camera, CTX and HiRISE) of Mars also have depth/diameter ratios of about 0.2 [ Daubar and McEwen , ; Daubar et al ., ]. Secondary craters, if present, appear to have a depth/diameter ratio of about half (0.1) that of primary craters [ Pike and Wilhelms , ].…”

Dependence of secondary crater characteristics on downrange distance: High‐resolution morphometry and simulations

“…For craters with L ≥250 km ( v i ≥ 0.95–1.1 km/s) and D ≥60 m, we found that the median is 0.112, with an average of 0.116 and standard deviation 0.035. About 3% of craters in this size range have d / D ≥0.2, a value typical of primaries on Mars of this size [ Daubar et al , ; Watters et al , ]. For craters with D ≥100 m in this range ( L ≥250 km) we found that the median is 0.127, with an average of 0.130 and standard deviation 0.033.…”

“…Simple primary impact craters on Mars that exhibit signs of good preservation have h / D ≈0.035 and d / D = 0.18 ± 0.04 [ Watters et al , , Table 3]. For fresh small primaries ( D < 35 m), d / D ≈0.23 on average [ Daubar et al , ]. That is, we find that diameter‐normalized rim heights and crater depths typical of primary craters occur in our simulations for v i ≥1.25 km/s.…”