AAS 201st Meeting, January, 2003
Session 29. HAD II: History of IDEAS on Extraterrestrial Life
Special, Monday, January 6, 2003, 10:00-11:30am, 612

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[29.03] Billions of Planetary Systems: Turning Point at Mid-20th Century

S. J. Dick (USNO)

The search for planetary systems, an elusive goal for most of the 20th century, is reminiscent of the search for stellar parallax in earlier centuries. Of the latter, John Herschel once wrote that it seemed within reach of the astronomer, “only to elude his seizure when apparently just within his grasp, continually hovering just beyond the limits of his distinct apprehension, and so leading him on in hopeless, endless, and exhausting pursuit.” Such was the case for planetary systems, until the discovery of pulsar planets in 1992, and of planets around solar-type stars beginning in 1995.

For the early decades of the century the Jeans-Jeffreys tidal theory of planet formation via close stellar encounters predicted that planets should be very rare. But the 15 years between 1943 and 1958 saw a remarkable turning point in the fortunes of planetary systems. It began with Russell’s criticism of the Jeans-Jeffreys theory, but was fueled by the revival of a modified nebular hypothesis (von Weizsacker, 1944), developments in fields as diverse as double star astronomy (Kuiper, 1951), the measurement of stellar rotation periods (Struve, 1950), and geochemistry (Urey, 1952) and – most surprising of all – by claims that planetary systems, or their effects had actually been observed (Strand, 1943; Reuyl and Holmberg, 1943). Struve (1952) even suggested a means for planet detection by the radial velocity method. As Harlow Shapley made clear in his work Of Stars and Men: Human Response to an Expanding Universe (1958), the new cosmology was a continual force in the background favoring abundant planetary systems.

All this work was in the background as Peter van de Kamp played out his solitary search for planetary systems, culminating in the announcement (1963) of a planet around Barnard’s star. The limits that Herschel spoke of have now been breached, and the search is no longer solitary.

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