A few hours before the second Hubble observation, NASA's Swift telescope detected a powerful flash of radiation coming from the surface of the star, its X-ray emissions briefly quadroupling in brightness.
"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," Peter Wheatley, with the University of Warwick in the United Kingdom, said in a statement.
Scientists, who presented their research on Thursday, said the finding has significance for studying Jupiter-class planets, but also could explain the rocky "super Earths" found orbiting other stars. They theorize the bodies could be the remnants of massive planets that have completely lost their atmospheres.
Astronomers were able to separate the planet's light from the light of its parent star as it passed across the face of the star, relative to Hubble's point of view.
The study will be published in an upcoming issue of Astronomy and Astrophysics.