Mars in fiction the past; Mars is a setting rather than a goal. Mariner 4 in July 1965 found that Mars—contrary to expectations—is heavily cratered, with a very thin atmosphere. No canals were found; while scientists did not believe that Mars was a moist planet, the lack of surface water surprised them. Science fiction had so influenced real explorations of the planet, however—Carl Sagan was among the many fans who became scientists—that after Mariner 9 in 1971-1972, craters were named after Wells, Burroughs, and other authors. The Mariner and Viking space probes confirmed that the Martian environment is extremely hostile to life. By
Gravity Probe A Gravity Probe A Gravity Probe A (GP-A) was a space-based experiment to test the equivalence principle, a feature of Einstein's theory of relativity. It was performed jointly by the Smithsonian Astrophysical Observatory and the National Aeronautics and Space Administration. The experiment sent a hydrogen maser, a highly accurate frequency standard, into space to measure with high precision the rate at which time passes in a weaker gravitational field. Masses cause distortions in spacetime, which leads to the effects of length contraction and time dilation, both predicted results of Albert Einstein's theory of general relativity. Because of the bending of spacetime,