Johndale Solem origin of the shape of rubble-pile asteroids. His analytic theory of the breakup of comets by planetary tidal forces resulted in his calculation of the diameter and density of the parent comet of Shoemaker-Levy 9 as it was before breaking up in the tidal field of Jupiter in 1994 (1994a). Solem's research on interplanetary travel culminated in his MEDUSA concept, a nuclear explosive propelled spacecraft for interplanetary space travel (1994b). Gregory Matloff said this was "a surprising [propulsion] concept which might greatly reduce spacecraft mass." The concept inspired research and elaboration by the aerospace community. At the behest of NASA's
David H. Levy of Allusions to Celestial Events in Elizabethan and Jacobean Writing, 1572–1620." Starting in 2015, Levy has been donating his observing logs, which he has kept continuously since 1956, his personal journals since 1958, and his comet search records since 1965, to the Linda Hall Library of Science Library in Kansas City. The observing records are also on-line at the website of the Royal Astronomical Society of Canada. He lives in Vail, Arizona and is married to Wendee Levy. Levy and his wife hosted a weekly internet radio talk show on astronomy, which ended on February 3, 2011, with a planned