The search for a planet analogous to our own has taken one step closer with the discovery of the smallest extrasolar planet yet orbiting a star which could support life. It is about three and one-third times the size of Earth, much more in line with our home than the gas giants on the scale of Jupiter or Saturn we had been finding up to this point. (An even smaller planet has so far been found, but it is orbiting a pulsar. Pulsars spew highly powerful radiation, so it's highly unlikely that anything within their vicinity could survive).

The largest extrasolar planet ever found is a puffy one, according to scientists reporting in an upcoming issue of Astrophysical Journal.

The planet, TrES-4, is roughly 1.7 times the size of Jupiter, but has the density of balsa wood. This puts it in a strange class of objects known as puffy planets, which have extremely low densities. Astrophysicist Georgi Mandushev of the Lowell Observatory in Arizona told Space.com that the planet is way bigger than its supposed to be. In other words, standard planets of that mass should be much tinier.

Located about 1,400 light years from Earth, the planet orbits its sun in just three and a half days. When it passes in front of that star, astronomers can calculate its size. As for why its puffy, they're still trying to work that out.—Gregory Mone

(Image credit: Jeffrey Hall, Lowell Observatory)