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In addition, the uncertainties they learned from testing the method on the moon and Mars extends to the whole solar system: “All crater counting ages on other celestial bodies,” they warned, “are based on certain assumptions about the origin and impact rate of the impactors.” The take-home message from the paper was bleak: In general, statistics of small craters are affected by numerous factors, e.g., contamination of secondaries and different target properties.
Crater counting is a subjective process which causes more uncertainties to the results.
Some of those “other factors” include not knowing the incoming rate (impact flux), saturation criteria, differences in target properties, erosion rates, or what complicated resurfacing histories have occurred.
In addition, human judgment can bias the counts based on what individuals consider significant: “this problem is severe in small crater counts,” the authors noted, although it might be alleviated with automated counting methods in the future.
5/24/2012: Mike Wall, seni0r editor for Space.com, unwittingly illustrated the arbitrariness of crater count dating in an article on Live Science: “One of the Red Planet’s most mysterious landforms is probably 2 billion years older than has been thought,” he began, “suggesting it may have had a volcanic origin, a new crater count finds.” While not questioning the validity of the method, Wall wrote that different astronomers, all using crater counts, arrived at ages for the Medusae Fossae area on Mars of a few hundred million years (“very young”), then 1.6 billion years, and now, up to 3.8 billion years.Also, the size-frequency distributions of small rayed lunar and Martian craters of probable primary origin are similar to that of the Population 2 craters on the inner solar system bodies post-dating Late Heavy Bombardment.Dating planetary surfaces using the small crater populations requires the separation of primaries from secondaries which is extremely difficult.Worries about the crater count dating method, widely relied upon to infer ages of planetary surfaces, began emerging in 2005.Those worries have not subsided; they have only grown worse. We’ve kept track of the crater count crisis since 2005, when the problem of secondary craters was brought to light (10/20/2005, 6/08/2006, 9/25/2007, 3/25/2008, 7/25/2010).