Super-Earth in Six-Planet System May Have Oceans, Life - Wired (blog)

A newly discovered exoplanet joins the small but growing list of worlds other than our own that may host life.

The exoplanet is a super-Earth, having about seven times the mass of our home planet, but orbits its parent star at roughly the same distance as Earth does from the sun. The star, HD 40307, is located about 42 light-years from Earth in the constellation Pictor. It's what's known as an orange dwarf star, making it somewhat smaller and dimmer than our sun, but not by much.

Three exoplanets were discovered around HD 40307 in 2008, but a team of European astronomers has reanalyzed data from the star and found the system contains three more worlds. This makes it look much more like our own solar system, with its eight planets.

The farthest planet in the HD 40307 system orbits with a period of about 200 days, a little more than half as long as our year, and is located about 56 million miles from its parent star. (In comparison, Earth is 93 million miles from the sun.) This puts it right smack in the star's habitable zone — the area around a star where liquid water might remain on the surface.

This super-Earth receives about two-thirds the amount of sunlight that our planet gets. It's a bit on the cold side, but still warm enough to have oceans and wet weather like on Earth. While scientists can't confirm that water exists on the planet, follow-up observations may give them more information.

About five other confirmed exoplanets have been discovered orbiting within a habitable zone but many of them are quite close to their parent star. This likely makes them suffer from a phenomenon known as tidal locking, where gravitational forces cause one side of the planet to always face the star. The same phenomenon is the reason why we always see the same face of the moon.

With exoplanets, this means that one half of the planet is probably roasting under the heat of its star while the other side is frozen in perpetual night. Because the new exoplanet around HD 40307 is far enough away from its star, it has a day/night cycle much like Earth's and therefore is probably much more conducive to life.

A paper about this discovery will be published in an upcoming issue of Astronomy & Astrophysics.

Video: Guillem Anglada-Escude that the University of Gottingen

Image: J. Pinfield, for the RoPACS network at the University of Hertfordshire