John A. O'Keefe

John Aloysius O'Keefe (1916–2000) was a planetary scientist with the National Aeronautics and Space Administration (NASA) from 1958 to 1995. He is credited with the discovery of Earth's "pear shape" using U.S. Vanguard satellite data collected in the late 1950s. He was the first to propose the idea of a scanning microscope in 1956 and he is the co-discoverer of the YORP effect (short for Yarkovsky-O’Keefe-Radzievskii-Paddock effect), an effect resulting from sunlight which causes a small celestial body such as an asteroid or meteor to spin up or down. O'Keefe was Roman Catholic.

During the early Project Apollo-era, O'Keefe was one of the major leaders in developing the American lunar science program and was instrumental in securing astrogeologist Eugene Shoemaker to work with NASA in developing a geology program for the Apollo astronauts.

Prior to the moon landings O'Keefe developed a theory that tektites, natural glass objects found in discrete strewn fields around the world, are actually volcanic ejecta from the Moon. He suggested that explosive, hydrogen-driven lunar volcanoes may be the mechanism that launched the tektites to Earth. After the moon landings his claim was apparently supported by a chemical analysis of a portion of lunar sample 12013 retrieved by Apollo 12 astronaut Pete Conrad that showed a similar major element composition to some tektites found in Southeast Asia. Some Apollo 14 samples also had chemistries similar to tektites. However, most other lunar data strongly challenged the O'Keefe hypothesis, and almost all researchers in this field now accept that tektites are of terrestrial origin, the products of large meteorite or cometary impacts on Earth. This is supported by geochemical, isotopic and mineralogical evidence, and the fact that most tektite strewn fields can now be confidently matched to known impact craters of similar age on Earth.

Several of O'Keefe's ideas about the physics of tektite formation, especially pertaining to Stokes' Law and the slow formation or 'fining' of tektites (apparently not possible in a rapid impact event), still remain as challenges to modern explanations of how tektites might have formed.