MANY Jupiter-like exoplanets are much larger than they ought to be. Now one astronomer thinks he knows why.

Since planets usually form at the same time as stars, astronomers can tell how old and therefore how hot and puffy the gas giants should be. But many of the recently discovered gaseous exoplanets are larger than expected.

 

Eduardo Martin of the Institute of Astrophysics of the Canary Islands believes this is because the puffy planets formed from the gas and dust ejected when two binary stars merged. This would make the planets much younger than their hosts, which would explain their unusual heat and puffiness. He presented his findings at the American Astronomical Society meeting in Boston last week.

 

"The process is possible, but it's unlikely to explain the multitude of inflated planets that we're now discovering," says Adam Burrows of Princeton University, who was not involved in the research.

 

Martin agrees that there are too few binary systems to account for the number of puffy planets seen. But he thinks that's because the number of binaries has been underestimated, so he is now searching for the "missing" population.