Crater counting

Shield volcano in Tharsis region on Mars with marked borders, circles represent impact craters counted by crater counting method.

Crater counting is a method for estimating the age of a planet's surface. The method is based upon the assumptions that a new surface forms with zero impact craters, and that impact craters accumulate at an estimated rate. The method has been calibrated using the ages obtained by radiometric dating of samples returned from the Moon by the Luna and Apollo missions.

Crater counting and secondary craters

Secondary craters (also known as secondaries) are craters formed by a primary impact. It might be recognized by its particular shape different than a primary crater. Secondaries can appears in clusters.

The accuracy of age estimates of geologically young surfaces based on crater counting on Mars has been questioned due to formation of large amounts of secondary craters. In one case, the impact that created Zunil crater produced about a hundred secondary craters, some more than 1000 km from the primary impact. If similar impacts also produced comparable amounts of secondaries, it would mean a particular crater-free area of Mars had not been "splattered by a large, infrequent primary crater", as opposed to suffering relatively few small primary impacts since its formation.[1]

See also

References

  1. ↑ Kerr, R (2006). "Who can Read the Martian Clock?". Science. 312 (5777): 1132–3. doi:10.1126/science.312.5777.1132. PMID 16728612.

Further reading

  • McEwen, A; Bierhaus, E (2006). "The importance of secondary cratering to age constraints on planetary surfaces". Annual Review of Earth and Planetary Sciences. 34: 535–567. Bibcode:2006AREPS..34..535M. doi:10.1146/annurev.earth.34.031405.125018.


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