Exoplanet Gets Partially Evaporated By Host Star
June 28, 2012

Exoplanet Gets Partially Evaporated By Host Star

Lee Rannals for redOrbit.com - Your Universe Online

Astronomers have observed one planet in another solar system, similar to Jupiter, giving off a powerful burst of evaporation after passing by its parent star.

Using the Hubble Space Telescope, astronomers saw exoplanet HD 189733b bathe in an intense X-ray radiation after its parent star gave off a violet flare.

The team observed the planet with Hubble during early 2010 and late 2011, during which HD 189733b was silhouetting its parent star. The planetary system lies so close to Earth, at 63 light-years away, that it can be seen with binoculars.

During observations, the planet's atmosphere imprints its chemical signature on the starlight, allowing astronomers to decode what is happening in the alien solar system.

The team carried out the observations to confirm what they had seen in a different planetary system, which was the evaporation of an exoplanet's atmosphere.

HD 189733b is a giant gas planet similar to Jupiter, but lies extremely close to its parent star at just one thirtieth the distance Earth is from the Sun.

The planet's climate is 1,832 degrees Fahrenheit, and its upper atmosphere is constantly being bombarded by energetic extreme-ultraviolet and X-ray radiation.

“The first set of observations were actually disappointing, since they showed no trace of the planet´s atmosphere at all," astronomer Alain Lecavelier des Etangs said in a press release, "We only realized we had chanced upon something more interesting when the second set of observations came in."

The second observation made in late 2011 showed a dramatic change, with clear signs of a plume of gas being blown from the planet at a rate of at least 1,000 tons per second.

"We hadn´t just confirmed that some planets´ atmospheres evaporate,” Lecavelier said in the release, “we had watched the physical conditions in the evaporating atmosphere vary over time. Nobody had done that before."

The evaporation is thought to have been caused by the intense X-ray and extreme-ultraviolet radiation from the parent star, which is about 20 times more powerful than the Sun.

Because the giant planet is so close to its star, the astronomers assume it suffers an X-ray dose 3 million times higher than the Earth.

A few hours before the astronomers used Hubble to observe the planet for the second time, NASA's Swift satellite captured a powerful flash of radiation coming from the surface of the star.

"X-ray emissions are a small part of the star´s total output, but it is the part that it is energetic enough to drive the evaporation of the atmosphere," Peter Wheatley (University of Warwick, UK), one of the co-authors of the study, said in a press release. "This was the brightest X-ray flare from HD 189733A of several observed to date, and it seems very likely that the impact of this flare on the planet drove the evaporation seen a few hours later with Hubble."

The X-rays hitting the upper atmosphere cause such extreme heat, that it causes the gas to escape the gravitational pull of the planet.

The researchers are publishing their findings in the upcoming issue of Astronomy and Astrophysics.