1993, 3rd edition 2005) See also Giant impact hypothesis Viktor Safronov References External links William Hartmann's Home Page 1939 births Living people People from Westmoreland County, Pennsylvania Novelists from Pennsylvania 20th-century American novelists 20th-century American astronomers 21st-century American astronomers American science writers American science fiction writers American male novelists American UFO writers American artists Space artists Eberly College of Science alumni Planetary scientists Ufologists University of Arizona alumni American male short story writers 20th-century American short story writers 21st-century short story writers 20th-century American male writers 21st-century American male writers 20th-century American non-fiction writers 21st-century American non-fiction writers American male non-fiction writers Barringer Medal winners American historical fiction writers