Astronomers said Wednesday that they had discovered a planet that is composed mostly of water, bringing scientists one step closer to finding a habitable planet.
A team of researchers at the Harvard-Smithsonian Center for Astrophysics found the planet, described as a "super-Earth" but too hot to sustain life at 400 degrees Fahrenheit on the ocean surface.
"Despite its hot temperature, this appears to be a waterworld," said Zachory Berta, a graduate student at the Harvard-Smithsonian Center for Astrophysics (CfA) who first spotted the hint of the planet among the data, in a statement. "It is much smaller, cooler, and more Earthlike than any other known exoplanet."
The planet, which is likely enveloped in a fog of superheated steam and other gases, offers concrete evidence that yes, it's possible that a planet as hospitable as Earth is outside our solar system.
The new extrasolar planet is 2.7 times the size of Earth and 6.6 times as massive. That means it takes 38 hours to circle its star, a dim red dwarf named GJ 1214 that's one-fifth the size of our Sun, in the constellation Ophiuchus, located about 40 light-years from Earth.
A "super-Earth" is defined as a planet between one and ten times the mass of the Earth. The new planet, officially named GJ 1214b, is one of the two smallest transiting worlds astronomers have discovered. Density measurements suggest that the planet is composed of three-fourths water and other ices, and one-fourth rock. (Earth is 0.06 percent water.)
The discovery adds GJ 1214b to a lengthening list of "super-Earths."
An international team of astronomers using telescopes in Australia and Hawaii reported in one paper that they had found three planets, including a super-Earth, orbiting 61 Virginis, a star in the constellation Virgo that is almost a clone of the Sun. In a separate paper, they reported finding a planet somewhat larger than Jupiter at the star 23 Librae. It was the first time, they said, that a super-Earth had been found belonging to a star like the Sun; the other home stars have been dwarfs.
And in yet another paper, a subset of the same group reported finding a super-Earth and probably two bigger planets circling HD 1461, a star in Cetus.
The new planet is so cool, relatively speaking, because of the dimness of its star, which delivers just one three-hundredth the energy of our own Sun.
The researchers had deliberately set out to search for planets around these kinds of stars, which are more numerous than those that match our own Sun.
Led by David Charbonneau, the team used a collection of eight telescopes on Mount Hopkins in Arizona. Each only 16 inches in diameter -- no bigger than those that found in the backyards of amateur astronomers -- the telescopes monitor the light of 2,000 nearby stars in search of "blips" caused by planetary movement.
Berta found a series of blips that occurred every 1.6 days exactly.
The next challenge? Finding a planet with a habitable atmosphere, one that's cool enough to prevent its water from boiling on its surface. The question is whether most planets orbiting dim red stars have such an atmosphere, which is hostile to life. If so, astronomers would have to seek even smaller stars for signs of life.
The researchers' findings will be published Thursday in the journal Nature.