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.

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.

Despite these facts, it should be noted that no impact crater associated with the massive 800,000-year-old Australasian tektite event has ever been found; undeniably, this single fact casts a nagging shadow upon the accepted impact model and is rarely mentioned when discussing tektites. Also, to compound the problem, craters associated with tektite strewnfields may be 'connate' (that is, not the source of the tektites by rather the by-product of the tektite event) as suggested in the 1970s by the late Dean R. Chapman of NASA. 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), also remain as challenges to modern explanations of how tektites might have formed.

Despite the scientific controversy that raged about tektites into the 1990s, O'Keefe made many valuable observations about tektites, and his books and many papers on the subject remain important reference works.

References

* Gray, M. "Angle of Attack: Harrison Storms and the Race to the Moon". W.W. Norton, New York: 1992.
* O'Keefe, J.A. (June 5, 1970) Tektite glass in Apollo 12 sample. "Science", Vol 168, 1209–1210.
* O'Keefe, J.A. (Feb. 26, 1985) The coming revolution in planetology. "Eos", Vol. 66, No. 9, pp. 89–90.
* O'Keefe, J.A. (1993) The origin of tektites. "Meteoritics", Vol. 29, No. 1, pp. 73–78.
* O'Keefe, J.A. (1976) "Tektites and Their Origin". Elsevier.
* Povenmire, H., O'Keefe, J.A., ed. (2003) "Tektites: A Cosmic Paradox". Florida Fireball Network.
* Varricchio, L. (2006) "Inconstant Moon: Controversy and Discovery on the Way to the Moon". Xlibris Books.
* Koeberl C. (1994) Tektite origin by hypervelocity asteroidal or cometary impact: target rocks, source craters, and mechanisms. "Geological Society of America Special Paper" Vol. 293, pp. 133–151.
* McCall GJH (2001) "Tektites in the Geological Record: Showers of Glass from the Sky". Geological Society of London, London.