No. 73: Jan-Feb 1991
In the November 16 issue of Science, R.A. Kerr remarks:
"The planetary geologists who are studying the radar images streaming back from Magellan [the space probe] find that they have an enigma on their hands. When they read the geological clock that tells them how old the Venusian surface is, they find a planet on the brink of adolescence. But when they look at the surface itself, they see a newborn babe."(Kerr, Richard A.; "Venus Is Looking Too Pristine," Science, 250:913, 1990.)
Comment. Of the 75 craters mapped so far by Magellan, only one shows any signs of aging; i.e., tectonic movements, lava-filling, etc. The surface of Venus should be hundreds of millions of years old, yet it looks freshly minted. The anticipated spectrum of degradation has not yet been seen.
One theory is that recent lava flooding erased the old craters, and we now see only recent impact scars. But why would a planet's volcanism turn off so completely and so abruptly? Our earth, Venus' sister planet in many ways, still perks away, leaving craters of various ages. Why is Venus so different? One idea not advanced by Kerr in Science is that Venus might be a recently acquired member of the solar system!