A "hot Jupiter" and its host star shed light -- literally -- on the interaction between a solar flare and a giant planet's atmosphere.
Exoplanet HD 189733b is a gas giant located 63 light-years away from Earth -- so close to us that its star can be observed with mere binoculars. The planet circles said star, HD 189733A, at a distance of only 3 million miles -- meaning that it's about 30 times closer to its star than the Earth is to the sun. Exoplanet HD 189733b, in size and environment, is similar to Jupiter, leading to its excellent classification as a "Hot Jupiter." And its nearness to Earth, combined with its size and its proximity to its star, makes it an ideal subject for astronomers who study the processes that drive atmospheric escape.
Exoplanet HD 189733b periodically transits its parent star. When that happens, the crossing gives astronomers an opportunity to probe the Hot Jupiter's atmosphere and environment to help them understand the details of atmospheric evaporation. When the transit occurs, some of the starlight passes through the planet's atmosphere. And that interaction imprints information about the composition and motion of the planet's atmosphere into the starlight itself.
In a previous study, a group led by Lecavelier des Etangs in France used the Hubble Space Telescope to document hydrogen gas escaping from HD 189733b's upper atmosphere. The finding made the planet the second known "evaporating" exoplanet at the time.
Now -- and, again, with the help of the Hubble -- a team of astronomers have made a new discovery about the Hot Jupiter, using a similar starlight-imprinting technique. In "an unparalleled observation," the scientists have detected what NASA calls "significant changes" in the exoplanet's atmosphere. NASA's Swift multi-wavelength observatory detected the star blasting out a strong X-ray flare -- one powerful enough to blow away part of HD 189733b's atmosphere. As one researcher put it: "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."
The image above -- which is, alas, simply an artist's rendering of the event -- depicts the evaporation of the planet's atmosphere in response to its host star's eruption.
And the video below -- also a rendering -- depicts the full motion of the transit: