Super-Earth joins ranks in life-supporting zone

Astronomers on the prowl for potentially habitable planets have found a new candidate: a world seven times as massive as Earth in a nearby solar system.

The planet orbits a star about 42 light-years away in the constellation Pictor. The star, HD 40307, was thought to harbor only three planets, but sensitive data-filtering methods revealed the presence of three more. The farthest-out of these lies in a “sweet spot,” at a distance from its star where liquid water — and thus life — could exist.

“It’s the position of the planet in its orbit that’s important,” says astronomer Hugh Jones of the University of Hertfordshire in England, a coauthor of the study to be published in an upcoming Astronomy & Astrophysics. The planet orbits close enough to its sunlike star that it could have similar temperatures to Earth. Furthermore, “the planet is not putting the same face to its star all the time, like the moon,” Jones says, so it should have cycles of day and night.

Jones and his colleagues detected the new planets from changes in the light of the host star as the planets’ gravity tugged on it. Instead of analyzing all the light from the star, however, the scientists split the light into different wavelengths to pick out the planets’ signals from those caused by the star itself. “With this technique, we were able to look more deeply into the data and detect weaker signals,” says Jones.

To date, only a handful of planets have been discovered in the habitable region around their stars. Nothing is known yet about the new planet’s physical and geochemical properties. But it would make a good target for a space-based imaging mission, its discoverers say, because it is so close to Earth. Another possibly habitable super-Earth, known as Kepler-22b, is much farther away, about 620 light-years from Earth.

Ultimately, the aim of this research is to constrain the types of solar systems that might support life, says Jones. “The more stars and solar systems are like our sun and its solar system, the more interesting they are to study.”