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 that the planet is “way bigger than it’s 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 it’s puffy, they’re still trying to work that out.—Gregory Mone

(Image credit: Jeffrey Hall, Lowell Observatory)