← Francys Distefano-Arsentiev, on Mount Everest, in this undated handout photo, was the first American woman to reach the summit of Mount Everest without bottled oxygen. Distefano-Arsentiev, along with her husband Serguei Arsentiev, of Norwood, Colo., died on the mountain, after the successful ascent May 23, 1998. No one knows exactly why the couples' descent turned deadly, but officials think the two were weakened after spending three nights at such a high elevation. (AP Photo/Lexington Herald-Leader, HO) →