Scientists said they believe the atmospheric variations occurred in response to a powerful eruption on the surface of the planet's host star, an event observed by NASA's Swift satellite, the space agency reported Thursday.
"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," lead researcher Alain Lecavelier des Etangs at the Paris Institute of Astrophysics said.
The observed exoplanet is HD 189733b, a gas giant similar to Jupiter circling its star at a distance of just 3 million miles, or about 30 times closer than Earth's distance from the sun.
The planet's parent star is just 63 light-years away from Earth, close enough to be seen with binoculars near the Dumbbell Nebula and giving astronomers an excellent opportunity to study 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," researcher Vincentg Bourrier said.
The researchers say they've determined at least 1,000 tons of gas was leaving the planet's atmosphere every second at speeds greater than 300,000 mph.
"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 study co-author Peter Wheatley, a physicist at the University of Warwick in England.