The ill-fated Mars Polar Lander, last heard from on Dec. 3, 1999, as it started a descent to the surface of the Red Planet, may be lying crippled in a huge crater, the chief mission scientist said on Thursday. But Richard Zurek, the Mars Polar Lander Project Scientist, said the crater theory was just one of several scenarios being considered by scientists at NASA’s Jet Propulsion Laboratory in Pasadena.