In the past year, astronomers searching for planets around other stars have found alien worlds that are smaller and younger than any previously known. The discoveries fill in details about how planets form and bring researchers even closer to the ultimate prize: “We’re on our way to finding an extrasolar earth,” says Barbara McArthur of the University of Texas at Austin.
In August Paul Butler of the Carnegie Institution of Washington and Geoffrey Marcy of the University of California at Berkeley described a body as little as 21 times the mass of Earth orbiting the nearby star Gliese 436, 33 light-years away. That’s about half the mass of the previous lightweight record holder. In short order, McArthur and her colleagues reported a planet about 18 times the mass of Earth around 55 Cancri, a star with three other planets, and a team led by Nuno Santos of the University of Lisbon in Portugal discovered a roughly 14-Earth-mass planet. These worlds may be rocky bodies, a lot more like Earth than the giant gas balls discovered previously.
Other studies are showing how planets form. In May researchers using the Spitzer Space Telescope reported evidence of an infant planet, possibly less than a million years old, taking shape near the star CoKu Tau 4. In August Michael Liu of the University of Hawaii described two large clumps in the disk of dust around another youthful star, AU Microscopii—signs of planets under construction.
More amazing discoveries are close at hand. Ian Bond of the Institute for Astronomy in Edinburgh, Scotland, and colleagues found a planet by watching how its gravity amplifies the light of a more distant star, a promising technique called gravitational microlensing. The Trans-Atlantic Exoplanet Survey, which looks for the shadow of a planet moving between us and its star, uncovered a Jupiter-size world using just a 4-inch telescope. And in April, Gael Chauvin of the European Southern Observatory and his team took the first direct photo of a possible planet around another star and managed to study its light.