Strange Planet Sports 9-Million-Mile Tail

Astronomers have discovered a bizarre entity about 30 light-years from Earth. The Neptune-sized planet, which has been labeled Gliese 436b, is being trailed by a comet-like tail that extends over 9 million miles. But it's the contents of this strange tail that may provide clues to other atmospheres within the cosmos.

The massive tail was detected using the Hubble Space Telescope, along with the Chandra X-Ray Observatory, which was launched on July 23, 1999 and has since provided the most detailed X-ray views yet of the universe.

Scientists believe the exotic tail is composed mostly of hydrogen gas, which is actually a continuation of a 1.8 million mile diameter circular head of gas surrounding the planet. The extensive tail is unprecedented for such a small exoplanet, and is believed to be the result of the planet's atmosphere evaporating into space due to intense radiation being emitted from its host star. The tail's composition has helped elucidate the small planet's history.

"This cloud of hydrogen is very spectacular," writes David Ehrenreich, an astronomer at the Observatory of the University of Geneva in Switzerland and lead author of a study describing the planet's tail. "Although the evaporation rate doesn't threaten the planet right now, we know that the star, a faint red dwarf, was more active in the past. This means that the planet's atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that it may have lost up to 10 percent of its atmosphere."

The planet's proximity to its host star may also be a factor. Gliese 436b orbits at a mere 4 million kilometers distance from its star, compared to Earth, which orbits the sun from about 150 kilometers away. And because of its proximity, it takes Gleise 436b less than 36 hours to orbit its nearby sun.

So the hunt is on for other exoplanets that may sport such impressive tails.

According to Vincent Bourrier, an astronomer and co-author of the paper, which appeared in the June 24 issue of the journal Nature, there could be thousands of similar planets yet to be discovered.

"Finding the cloud around Gliese 436b could be a game-changer for characterizing atmospheres of the whole population of Neptunes and Super-Earths in ultraviolet observations," he said.

Scientists will just have to keep looking.