A rocky exoplanet about the size of Mercury appears to be evaporating before our eyes. If confirmed, this would be the first time a rocky planet has been found turning to gas, demonstrating just how wacky alien planets can be. The provocative suggestion may also foreshadow the fate of Mercury.
"My first reaction was disbelief," says Dan Fabrycky of the University of California, Santa Cruz, who was not involved in the new analysis. After playing with the data himself, however, he has come around – though he is still cautious. “After turning it over in my mind a few days, I cannot come up with a more natural theoretical explanation,” he says.
The evaporation was inferred from observations by NASA’s Kepler space telescope. These show that a star called KIC 12557548, which is slightly smaller than the sun, is dimming every 15.685 hours precisely. That suggests an orbiting companion is transiting, or passing in front of the star. Unlike other transits seen by Kepler, though, the dimming in this system varies wildly from one pass to another.
The best explanation is a rocky planet about the size of Mercury that is subliming – turning directly to a gas - due to the intense radiation from its star, conclude a team led by Saul Rappaport of Massachusetts Institute of Technology.