It was front-page news when astronomer Paul Kalas of the University of California, Berkeley, and his team produced the first photographic evidence of a planet orbiting another star last month. (Another team, publishing simultaneously, announced similar results around a different star.) But at least one person in the field was not surprised: astronomer Alice Quillen of the University of Rochester had predicted the existence of just such a planet, in just such an orbit, in the Monthly Notices of the Royal Astronomical Society: Letters in October 2006.
Two years ago, Quillen examined the debris disk around a star 25 light-years away known as Fomalhaut. She hypothesized that the features of the disk implied that there ought to be a planet, whose mass lay between that of Neptune and Saturn, orbiting nearby, some 119 astronomical units (AU) from Fomalhaut. (An astronomical unit is roughly the distance between Earth and the sun.)
What Kalas and his team found mirrored Quillen's foreshadowing: the planetary candidate, dubbed Fomalhaut b, has a mass likely between that of Neptune and a few times that of Jupiter, and it orbits at 119 AU from the star. It's worth noting that Kalas and two collaborators predicted a planetary system around Fomalhaut in 2005, but Quillen took that concept a step farther the following year by laying out specifics of what such a planet would look like and where it should be.
Image of Fomalhaut system courtesy of NASA, ESA, P. Kalas, J. Graham, E. Chiang, E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center), M. Fitzgerald (Lawrence Livermore National Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory)