NASA's Hubble Detects Evaporating Exoplanet
Spectacular events on a planet outside our solar system have given NASA scientists a view of an exploding star and the planet that orbits it emitting an intense plume of gas.
The exoplanet, called HD 189733b, is a gas giant similar in size to Jupiter that circles a star at a distance of only 3 million miles - that's 30 times closer than Earth's distance from the sun. It completes this orbit every 2.2 days, circling a star that is 80 percent the size of our sun.
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Even though its star is slightly smaller and cooler than the Sun, this makes the planet's climate exceptionally hot, at above 1000 degrees Celsius, and the upper atmosphere is battered by energetic extreme-ultraviolet and X-ray radiation, reports The Daily Mail.
When HD 189733b crosses in front of its star in a transit, scientists are able to use the backlighting from the star to see the planet's atmosphere to learn about its composition. In April 2010, the 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 striking evidence that at least 1,000 tons of gas were leaving the planet's atmosphere every second in a 300,000 mile per hour stream of hydrogen atoms.
"We hadn't just confirmed that some planets' atmosphere evaporate, we had watched the physical conditions in the evaporating atmosphere vary over time," said study leader Alain Lecavelier des Etangs, of the National Center for Scientific Research in France, according to MSNBC. "Nobody had done that before."
Using the Swift satellite, they observed a powerful explosion from the star just as the planet was about to make its transit. The enormous flare brightened the star by 3.6 times in X-rays.
"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," said co-author Peter Wheatley, a physicist at the University of Warwick in England.
The system is close enough - just 63 light-years away - that its star can be viewed with binoculars. This makes HD 189733b an ideal target for studying the processes that drive atmospheric escape.
"Astronomers have been debating the details of atmospheric evaporation for years, and studying HD 189733b is our best opportunity for understanding the process," said Vincent Bourrier, a doctoral student at the Paris Institute of Astrophysics and a team member on the new study.
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