Secondary craters – you know, the kind that are created by the falling debris that follows an initial impact – are what scientists call… annoying.
This is because they can muddy up crater counts, which scientists use to determine the age of a planetary surface (the more craters found in an area, the older it is, generally).
But in a new paper published in the journal Icarus, Planetary Science Institute Associate Research Scientist Jack Conrad explains how secondary craters can actually be used to scientific advantage. By comparing secondary craters from an impact across geologic contacts – the boundary between two different kinds of surface, like lava flows and landslides, for example – researchers can infer important differences in surface material properties such as strength and porosity.
“It’s like having an annoying little brother who actually does something good for once,” Conrad said.
Scientists can tell regular craters from secondary craters in a number of ways. Secondary craters are usually created in batches; They’re small and oblong and point back to the original impact area.
If scientists find a set of secondary craters that fall across a geological contact, then they can compare the crater size across the two surfaces. In the paper, Conrad and his coauthor worked out the math to ultimately translate crater size distributions into differences in material properties.
“If someone is counting craters or doing a geologic survey for a completely different reason and happens upon a cluster of secondaries that crosses a geologic border, I want them to remember this paper and want to give it a try,” Conrad said.
He also stressed that this can be applied anywhere in the Solar System that hosts secondary craters.
“I also think it might end up being useful to sort of rethink scaling laws,” Conrad said. “The math in the paper relies on equations made from empirical studies. We have small scale lab experiments that are great for micrometer impacts to the centimeter scale, and most impact research is on large kilometer-plus diameter and kilometer-per-second-class impacts. Yet there is a gap in the slower, smaller impacts common during secondary cratering.”
Conrad also hopes that with this information, others will revisit material properties, such as surface porosities, reported in past studies.
