Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51c1448b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P51C-1448
Physics
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Important to understanding the mechanisms of basin ring formation on planetary bodies have been analyses of peak-ring basins (exhibiting a rim crest and an interior ring) and protobasins (a rim crest and interior ring plus a central peak), which have rim-crest diameters and interior morphologies that occur within the transition between complex craters with central peaks and multi-ring basins. While many catalogs of these basin types have been produced, recently acquired spacecraft data for the Moon, Mars, and Mercury have permitted improved portrayal and classification of these basins' features. We used new gridded topographic data from the Lunar Orbiter Laser Altimeter (LOLA) combined with Lunar Orbiter image mosaics to conduct a survey of craters >50 km in diameter on the Moon and to update the existing catalogs of lunar peak-ring basins and protobasins. We measured the diameters of basin rim crests, rings, and central peaks (where present) by visually fitting circles to these features using geographical information systems (GIS) software. Our updated catalog includes 17 peak-ring basins (rim-crest diameters range from 207 km to 582 km, mean = 353 km) and 3 protobasins (137-170 km, mean = 158 km). We also include in our catalog 28 craters exhibiting small ring-like clusters of peaks (50-205 km, mean = 83 km); at least some of these craters may exhibit morphologies uniquely transitional to the process of forming basin rings. A power-law fit to ring diameters (Dring) and rim-crest diameters (Drim) of peak-ring basins on the Moon [Dring = 0.13±0.09(Drim)1.23±0.06] reveals a trend that is very similar to a power-law fit to peak-ring basin diameters on Mercury [Dring = 0.25±0.14(Drim)1.13±0.10] (Baker et al., 2010, Lunar and Planet. Sci. 41, no. 1384). A plot of ring/rim-crest ratios versus rim-crest diameters for lunar peak-ring basins and protobasins also reveals a continuous, nonlinear trend that is similar to trends observed for Mercury and Venus and suggests that protobasins and peak-ring basins are parts of a continuum of basin morphologies. The surface density of peak-ring basins on the Moon (4.5 x 10-7 per km2) is a factor of two less than Mercury (9.9 x 10-7 per km2), which may be a function of their widely different mean impact velocities (19.4 km/s and 42.5 km/s, respectively). The onset diameter for peak-ring basins on the Moon is also the largest in the inner solar system. Comparisons of the predictions of basin-formation models with the characteristics of our new basin catalog for the Moon suggest that formation and modification of an interior melt cavity and nonlinear scaling of impact melt volume with crater diameter provide important controls on the development of peak rings. In particular, a power-law model of growth of an interior melt cavity with increasing crater diameter is very consistent with the power-law fits to the data for the Moon and Mercury. Furthermore, we suggest that onset diameters for peak-ring basins on the terrestrial planets are likely to be dependent on both the planet's surface gravitational acceleration and mean impactor velocity, and that depth of melting is likely to be a controlling parameter in determining these onset diameters.
Baker Mark D.
Fassett Caleb
Head James W.
Kadish Seth
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