The Magellan spacecraft was launched in May 1989 and began mapping the surface of Venus in September 1990. The spacecraft continued to orbit Venus for four years, returning high-resolution images, altimetry, thermal emissions and gravity maps of 98 percent of the surface. Magellan spacecraft operations ended on October 12, 1994, during its controlled descent into the deeper portions of the Venusian atmosphere.
The surface of Venus is displayed in these
five global views. The center image (A) is centered at Venus's north pole. The other four images are centered around the equator of Venus at (B) 0 degrees longitude, (C) 90 degrees east longitude, (D) 180 degrees and (E) 270 degrees east longitude.
Data gaps are filled with Pioneer-Venus Orbiter altimetric data, or a constant mid- range value. Simulated color is used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft.
The scattered dark patches in this image are halos surrounding some of the younger impact craters.
Based on the random distribution of impact craters and the limited number of tectonized or volcanically flooded craters on Venus, it has been proposed that Venus experienced a catastrophic resurfacing event 300-500 million years ago. In this a model, there has been little subsequent volcanic and tectonic activity, with the surface acting primarily as a passive accumulator of impact craters. This global data set reveals a number of craters consistent with an average Venus surface age of 300 million to 500 million years.
Magellan has completed our first-order reconnaissance of Venus, much as the Viking spacecraft did for Mars. So where do we go from here?
From the standpoint of solid-body studies, the most valuable follow-up missions involve landing spacecraft on the surface. Particularly useful would be one or more sample return missions, which would allow detailed sample petrology and geochemistry measurements, including radiometric age dating, to beperformed. Unfortunately, this is likely to be a long time in coming given the current fiscal climate.
From a geophysics perspective, a network mission to deploy seismometers and measure heat flow at various locations would be of great value. Such a mission would require a significant technology breakthrough to allow long mission durations at the very high Venus surface temperature, which again seems unlikely for the foreseeable future.
Compiled by Guy McArthur from a JPL press release and an article in the Lunar and Planetary Information Bulletin by Walter S. Kiefer
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