Disintegrating Mercury-like Exoplanet Found

May 18, 2012 by Sci-News.com

A team of astronomers has detected a possible planet, some 1,500 light years away, that appears to be evaporating under the blistering heat of its parent star.

Artist’s impression of a Mercury-like exoplanet orbiting the star KIC 12557548 (NASA)

The scientists infer that a long tail of debris – much like the tail of a comet – is following the planet, and that this tail may tell the story of the planet’s disintegration. According to the team’s calculations, the tiny exoplanet, not much larger than Mercury, will completely disintegrate within 100 million years.

Based on data from the Kepler Observatory, the team found that the dusty planet circles its parent star dubbed KIC 12557548 every 15 hours – one of the shortest planet orbits ever observed. Such a short orbit must be very tight and implies that the planet must be heated by its orange-hot parent star to a temperature of about 3,600 degrees Fahrenheit.

Researchers hypothesize that rocky material at the surface of the planet melts and evaporates at such high temperatures, forming a wind that carries both gas and dust into space. Dense clouds of the dust trail the planet as it speeds around its star.

“We think this dust is made up of submicron-sized particles,” said Saul Rappaport, a professor emeritus of physics at the Massachusetts Institute of Technology and co-author of a paper in the Astrophysical Journal. “It would be like looking through a Los Angeles smog.”

The astronomers considered several explanations for the puzzling data, including the possibility that a planetary duo — two planets orbiting each other — also orbited the star. In the end, the data failed to support this hypothesis: The dimming every 15 hours was judged far too short a period to allow sufficient room for two planetary bodies orbiting each other, in the same way that Earth and the Moon together orbit the Sun.

Instead, the researchers landed on a novel hypothesis: that the varying intensities of light were caused by a somewhat amorphous, shape-shifting body.

“I’m not sure how we came to this epiphany,” Prof Rappaport said. “But it had to be something that was fundamentally changing. It was not a solid body, but rather, dust coming off the planet.”

The researchers created a model of the planet orbiting its star, along with its long, trailing cloud of dust. The dust was densest immediately surrounding the planet, thinning out as it trailed away. The group simulated the star’s brightness as the planet and its dust cloud passed by, and found that the light patterns matched the irregular light curves taken from the Kepler Observatory.

“We’re actually now very happy about the asymmetry in the eclipse profile,” Prof Rappaport said. “At first we didn’t understand this picture. But once we developed this theory, we realized this dust tail has to be here. If it’s not, this picture is wrong.”