The possibility of life on other planets has captured the imagination of the twentieth century, but before scientists can find extraterrestrial life they must find the planets themselves. Until a few years ago, the search for extrasolar planetary systems was more sci-fi than science. But with the development of powerful new spectrographs for measuring the wavelength of starlight, astronomers can now observe the "gravitational wobble"--a tiny shift in wavelength as a planet and star orbit each other--indicating a planet's presence.
Simply by analogy with our own solar system, scientists anticipated finding large Jupiter-like planets with long Jupiter-like orbital periods (11 years), recalls professor of astronomy Robert Noyes. But in 1995, when Swiss scientist Michel Mayor announced the first discovery of a planet orbiting a star, Noyes says that, "to everyone's surprise, the period of the planet was not anything like 11 years--or even one year. It was only four days."
This discovery forced astronomers to dramatically revise their views about the likely makeup of other solar systems. The brief orbit meant that the planet, despite its enormous size, was extremely close to its star, which, Noyes explains, is "very different from our own solar system, and very unexpected." The few astronomical teams searching for extrasolar planets had been seeking "wobbles" characterizing orbits of many years' duration. To see the "wobble" of Saturn on the sun, for example, "you've got to wait 30 years," he says.
Now the field of extrasolar planetary research has exploded. In 1997, Noyes, together with his colleagues Peter Nisenson and Sylvain Korzennik at the Harvard-Smithsonian Center for Astrophysics, announced the discovery of a ninth extrasolar planet, which orbits Rho Coronae Borealis, a sun-sized star in the Northern Crown constellation. The planet "is only about a quarter as far from its sun as our earth is from ours, and it's zipping around with a period of only 40 days," says Noyes. "That's not so astonishing--after all, Mercury's orbit is only 88 days. But Mercury is tiny, and this is a huge planet"--comparable in size to Jupiter. "Most of the planets seen so far have been giant planets that are close in--but that may be an accident of how well we can see them," Noyes explains, noting that the larger the planet, and the closer to its star, the bigger the observable wobble.
Late in June a tenth planetary discovery was announced independently by American and Swiss astronomers. This time the excitement stemmed from the size of the host sun--a star "only about 30 percent the size of our sun, and only about three times the minimum mass required to be a star at all," says Noyes. Eventually, "people may come to the conclusion that virtually every star has planets around it," he adds. If that proves true some day, the probability of discovering life beyond our solar system will increase dramatically. Although none of the planets discovered thus far are likely candidates for extraterrestrial life, says Noyes, "the diversity of possible abodes for life is much larger than we think if we simply take our own Earth and solar system as the model. The diversity of planetary systems around many different kinds of stars strongly suggests that life could very well be found."
~ Harbour Fraser Hodder