Number 36 (Story #3), May 31, 1991 by Phillip F. Schewe and Ben Stein THE MAGELLAN SPACECRAFT , having mapped 84% of Venus' surface, has finished its nominal mission. Its orbit will now be shifted slightly in order to do some additional mapping from a different perspective. Stephen Saunders of JPL said that because of repeated lava flows, the surface of Venus has an average age of only 400 million years. (The New York Times, 30 May 1991.)