Exoplanet HD 189733b Gets Blasted by Eruption From Its Host Star
Astronomers using data from NASA's Hubble Space Telescope have detected significant changes in the atmosphere of a planet (HD 189733b) located beyond our solar system. The variations occurred in response to a powerful eruption on the planet's host star, an event observed by NASA's Swift satellite. The artist's rendering above illustrates the evaporation of HD 189733b's atmosphere in response to a powerful eruption from its host star.
Lead researcher Alain Lecavelier des Etangs at the Paris Institute of Astrophysics (IAP), says, "The multiwavelength coverage by Hubble and Swift has given us an unprecedented view of the interaction between a flare on an active star and the atmosphere of a giant planet."
HD 189733b, a gas giant similar to Jupiter, but it is about 14% larger and more massive. The exoplanet is classified as a "hot Jupiter." Previous Hubble observations indicate the planet's deep atmosphere reaches a temperature of about 1,900 degrees Fahrenheit (1,030 C). The planet circles its star at a distance of only 3 million miles, which is about 30 times closer than Earth's distance from the sun. The planet is so close to its host star that it completes an orbit every 2.2 days. The planet's star, named HD 189733A, is about 80% the size and mass of our sun.
In April 2010, researchers observed a single transit using Hubble's Space Telescope Imaging Spectrograph (STIS), but they detected no trace of the planet's atmosphere. Follow-up STIS observations in September 2011 showed a surprising reversal, with evidence that a plume of gas was streaming away from the exoplanet. The researchers determined that at least 1,000 tons of gas was leaving the planet's atmosphere every second. Because X-rays and extreme ultraviolet starlight heat the planet's atmosphere and likely drive its escape, the team also monitored the star with Swift's X-ray Telescope (XRT). On Sept. 7, 2011, just eight hours before Hubble was scheduled to observe the transit, Swift was monitoring the star when it unleashed a powerful flare. It brightened by 3.6 times in X-rays, a spike occurring atop emission levels that already were greater than the sun's. The astronomers say HD 189733b encountered about 3 million times as many X-rays as Earth receives from a solar flare at the threshold of the X class.
Study co-author Peter Wheatley, a physicist at the University of Warwick in England, says, "The planet's close proximity to the star means it was struck by a blast of X-rays tens of thousands of times stronger than the Earth suffers even during an X-class solar flare, the strongest category."
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The findings by the international team of astronomers will appear in an upcoming issue of the journal Astronomy & Astrophysics.