Extrasolar Planets

In 1943, Danish-born United States astronomer K. A. Strand (1907–2000) reported a suspected companion to one of the components of the double star 61 Cygni, based on a slight wobble of the two stars' orbital motions. This seems to be the earliest report of an extrasolar planet; recent data have confirmed the presence of a planet with about eight times the mass of Jupiter orbiting the brighter component of 61 Cygni. Strand's estimate of a period of 4.1 years for the planet's orbit has also been confirmed.

In 1963, Dutch-born United States astronomer Peter van de Kamp (1901–1995) reported the detection of a planet orbiting Barnard's Star (Gliese 699) with a 24-year period of revolution. Barnard's Star, which is 5.98 light years away, is the second-closest star system to ours after the Alpha Centauri triple-star system. Van de Kamp suggested that Barnard's Star's wobbling proper motion could be explained by two planets in orbits with periods of revolution around Gliese 699 of 12 years and 26 years, respectively.

Independent efforts to confirm Strand's planet (or planets) orbiting Barnard's Star failed, however. By the 1970s, most astronomers had concluded that, instead of discovering extrasolar planets, both Strand's and van de Kamp's studies had only detected a slight systematic change in the characteristics of the telescope at the observatory where they had made their observations.

Astronomers kept looking, but for many years the search for extrasolar planets was marked by much-ballyhooed advances followed by summary retreats. No sooner would a group of astronomers announce the discovery of a planet outside of the solar system, than an outside group would present evidence refuting the findings discovery. A first breakthrough came in 1991, when it was shown that three approximately Earth-size planets orbit the pulsar PSR1257.12. (Subtle timing shifts in the flashes of the pulsar revealed the existence of the two planets; this is the first and, so far, only time that this technique has detected extrasolar planets.) No more discoveries were made for several years; then, in 1995, the dam broke. Using the radial-velocity technique extrasolar planet detection (to be explained below), group after group of astronomers announced extrasolar planet findings, findings quickly confirmed by other independent researchers. Suddenly, extrasolar planets went from rare to commonplace. At present over 100 planets have been detected and confirmed by the astronomical community.