Scientists find a 'super Earth.' Could it host life?

The newly discovered planet is five times Earth's mass and circles its sun every 13 days.

from the April 25, 2007 edition

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Benefits of a dwarf star's faintness

But Gliese 581 is a red dwarf, a small type of star that has only a third of the sun's mass and is at least 50 times fainter. So its habitable zone lies much closer to the star than the sun's. The team estimates that the planet they've discovered boasts an average surface temperature of between 0 and 40 degrees C (32 to 104 degrees F.).

"On the treasure map of the universe, one would be tempted to mark this planet with an X," says Xavier Delfosse, a researcher at Joseph Fourier University at Grenoble, France, and another member of the team.

The discovery is "truly awesome," agrees Dimitar Sasselov, a researcher at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Although he was not part of the team reporting the discovery, he is collaborating with the group on follow-up observations to help pin down the planet's traits with greater precision.

The team used an extremely sensitive planet-hunting detector, dubbed HARP, bolted to the back of the European Southern Observatory's 3.6-meter telescope at La Silla, Chile. HARP is said to be able to detect an object's velocity to within about two miles an hour of its actual value. Two years ago, HARP nabbed Gliese 581's first planet – similar in mass to Neptune. In the new data the team gathered on the second planet, astronomers also have seen strong evidence for a third planet. Preliminary indications suggest it's orbiting every 84 days and is about eight times more massive than Earth.

Along with Dr. Sasselov, the team is using Canada's "MOST" orbiting telescope starting this week to conduct follow-up studies. MOST is small by just about any standard. Its light-gathering mirror is only about 6 inches across, compared with the Hubble Space Telescope's 94-1/2-inch mirror or the Keck Observatory's twin mirrors, each nearly 400 inches across. Indeed, Canada's plucky instrument has earned a water-cooler name: the Humble Space Telescope.

But what it lacks in size it makes up for in sensitivity to subtle changes in starlight, Sasselov explains. The team will use that sensitivity to monitor Gliese 581 for slight changes in its light as its planets swing across its face.

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