sun

Extrasolar planet hunters are excited about a not-so-hot discovery. For the first time they’ve found a relatively cool extrasolar planet that they can study in detail. The finding is a milestone, says study coauthor Hans Deeg of the Instituto de Astrofísica de Canarias in Tenerife, Spain, because it is the first time astronomers have found an extrasolar planet that not only is cool enough to be similar in composition and history to the familiar solar system gas giants Jupiter and Saturn, but also passes in front of the star it orbits. Although a number of extrasolar planets with moderate temperatures have been discovered, only a planet that passes in front of — or transits — its star can be studied in depth. The starlight that filters through the atmosphere of the planet during each passage reveals the orb’s composition, while the amount of starlight that is blocked outright indicates the planet’s size.