Physics
Scientific paper
Mar 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982phdt........43b&link_type=abstract
Thesis (PH.D.)--CORNELL UNIVERSITY, 1982.Source: Dissertation Abstracts International, Volume: 42-12, Section: B, page: 4830.
Physics
3
Scientific paper
Radar images of Venus obtained in 1975 and 1977 with the Arecibo Observatory interferometer show details of approximately 25% of the surface at resolutions of 5 to 20 km. Some of the surface features observed are similar in appearance to craters in radar images of the moon. Over 30 of these, which range from 20 to 260 km in diameter, are identified as possible impact craters. If these features are impact craters then the diameter-frequency distribution of the observed crater density can be interpreted as an indication of how recently large-scale surface modification has occurred on Venus. The main objective in this project is to determine the crater density from the radar images and, from the diameter-frequency distribution, obtain an estimate of the "retention age" of the surface: the length of time a crater on Venus can retain its radar signature. The major problem faced in obtaining this objective is the ambiguity in identifying these features as impact craters. Endogenic features such as volcanic calderas are expected to have this same backscatter signature in radar images at this resolution. Radar-observable characteristics of these features that might suggest mode of origin are investigated. These include the crude morphology, basically planimetric shape, of the feature and its polarization signature. The applicability of Pioneer Venus altimetry results to this problem is also examined. It is concluded that it is not possible to distinguish impact craters on Venus from endogenic, principally volcanic, surface features on the basis of the presently available radar data. The cratering analysis is therefore restricted to finding an upper bound on the retention age. The observed density of the crater-like features indicates an age less than 2.7 (+OR-) 1 b.y. for craters with this radar signature. This implies that the surface of Venus is very young relative to the lunar mare, meaning that resurfacing of large portions of the surface has taken place since the lunar mare were formed and probably within the last 2.7 b.y.
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