Comparative Planetology
Diverse origins of catenae on Mercury (and elsewhere?)
David A Rothery
Emma Fegan (The Open University)
The Open University
There are only three named catenae on Mercury, each uncontroversially interpreted as a chain of secondary impact craters radial to a major impact. We have documented nearly 500 features on Mercury (up to 300 km long and 10-30 km wide) fitting the definition of catenae (chain of craters). Many of these cannot be related to an impact basin, and moreover there is a strong preference for orientations between NNW and NNE.
Chains of impact secondaries should have random trends (radial to each source). The visibility of such large features is unlikely to be strongly biased by solar illumination, so an explanation is required.
Catenae that divert round topographic features such as large crater rims are hard to reconcile with an impact origin, and may be volcanic or tectonic features. Additional unusual attributes of ’problem catenae’ include: 1) they may have a larger crater (twice the diameter of the rest of the chain) at one end; 2) their edges may lack the degree of scalloping characteristic of coalesced circular craters; 3) they may be unusually shallow.
However, some catenae that look like chains of impact craters could result from serial impact by fragments of tidally-disrupted comets, in which case the non-random orientations across Mercury’s surface could reflect a pattern in the orbital inclinations of comets with perihelia closer to the Sun than Mercury (present-day statistics for the comet population are biased around 144° because of the Kreutz sungrazers, from breakup of a single object).
Catenae on other bodies should be reassessed.
16:30 - 18:00