Visionary astronomers such as Frank Drake and the late Carl Sagan, and philosophers centuries before them, had long predicted that our solar system was not unique: that out in the reaches of space, other planets were circling other suns, and we had but to find them. Now it appears we have but they are not at all what we expected. Unlike our solar system, in which small rocky planets circle close to the Sun and cool gas giants orbit much farther out, in these new planetary systems, giant planets many times the mass of Jupiter seem to be orbiting in a veritable arm's length of their stars, or swooping by their suns in drastically elliptical orbits, totally unlike the near-circles traversed by Earth and its sisters.
Not since Pluto was discovered in 1930 had there been any new discovery of a planet orbiting a Sun-like star. Then, in October 1995, the Swiss astronomers Michel Mayor and Didier Queloz announced that they'd detected signs of a planet around the star 51 Pegasi in the constellation Pegasus. Since then, at least eight more planets have been detected orbiting distant stars, and even they, says one astronomer, "are only the tip of the iceberg."
Astronomers cannot actually see the new planets that have been discovered. They can only detect, by a regular change in the wavelengths of a star's light, that some enormous object at a particular distance, and of a particular mass is orbiting that star.
Now scientists are trying to get a grasp on the planets that have been found. Are they rocky like Earth or gaseous like Jupiter? Are they actually planets, or failed stars called brown dwarfs? If they are planets, how did such massive ones end up so close to their stars when conventional wisdom has always held that large planets could not form there? And could they or their moons harbor life?
Author and astronomer Stephen Maran guides us through the maze of fact and speculation surrounding these "new" planets discoveries that, for the moment, are providing far more questions than answers.