Big exoplanet may be surrounded by helium

The party balloon industry could make a killing on an exoplanet such as GJ 436b, a broiling Neptune-sized world whose atmosphere might contain mostly helium. No such planet orbits our sun, but helium planets might be common throughout the galaxy, researchers say.

Hydrogen dominates the skies over the giant planets Jupiter, Saturn, Neptune and Uranus. But if those planets were closer to the sun, the hydrogen would bake off and leave behind helium, Renyu Hu, an astrophysicist at the Jet Propulsion Laboratory in Pasadena, Calif., and colleagues suggest. Such a scenario could describe the plethora of “warm Neptunes” turned up by the Kepler space telescope, the researchers suggest online May 11 at arXiv.org.

A shroud of helium could explain the strange chemistry of GJ 436b, where researchers see no trace of the hydrogen-bearing methane that they expected. Astronomers have yet to determine, however, if the planet is ruled by a race of squeaky-voiced balloon suppliers.