Hubble spots strange new planet with evaporating atmosphere

Hubble spots strange new planet with evaporating atmosphere


Astronomers making use of the Hubble Space Telescope have been able to make measurements of changes in a distant exoplanet’s atmosphere for the first time, according to a report from NASA. After monitoring a powerful solar flare from the planet’s parent star, astronomers were able to detect noticeable changes in the planet’s atmosphere in response.

The planet in question is identified as HD 189733b, and it is in that class of exoplanets which pass directy in front of their parent stars as viewed from Earth. Such a pass in front of the star is referred to as a “transit”. The light traveling to Earth during such a transit can be examined to uncover details about the orbiting exoplanet.

“We hadn’t just confirmed that some planets’ atmosphere evaporate, we had watched the physical conditions in the evaporating atmosphere vary over time,” study leader Alain Lecavelier des Etangs, of the National Center for Scientific Research in France, said in a statement. “Nobody had done that before.”

Astronomers had previously determined that HD 189733b was a “hot Jupiter”, that is, a very large planet that orbits very close to its parent star. HD 189733b is about 14 percent more massive than Jupiter, and orbits only 3 million miles from its parent star. (For comparison, the innermost planet in our own solar system is tiny Mercury, which orbits over 28 million miles from the Sun, and our largest planets orbit in the farthest portion of our solar system.) This close orbit means that HD 189733b is subject to high temperatures, with an estimated internal atmospheric temperature of over 1900 degrees Fahrenheit.

During a previous transit, astronomers detected no signals from the planet’s atmosphere. Then, just hours prior to the scheduled observation of another transit, NASA’s Swift X-ray Telescope observed a massive X-ray flare on HD 189733b’s parent star, watching as the star brightened over 3.6 times in X-ray wavelengths.

Subsequently observing the transit of the planet across the face of the star with the Hubble Space Telescope, the astronomers detected signs that the planet’s atmosphere was streaming away from it into space. Peter Wheately, a co-author of the paper reporting the observations, explains, “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.”

Astronomers found that the planet seemed to be losing approximately 1,000 tons of gas from its atmosphere per second, blasted away by the star’s tremendous flare. Astronomers working on the project say the massive solar flare from the nearby star is likely the source  behind stripping the planet of its atmosphere.

“We noticed the flare just eight hours before the observation, so we suspect this is the reason for the evaporation event,” Mr. Lecavelier said.

The astronomers note that this is a remarkable example of being able to observe the interaction between a star’s activity and its effects on the atmosphere of an orbiting planet. Team member Vincent Bourrier says, “Astronomers have been debating the details of atmospheric evaporation for years, and studying HD 189733b is our best opportunity for understanding the process.”

The study could further shed light on how solar weather impacts planets, including Earth. Scientists studying solar weather in recent months have warned of possible consequences related to how solar storms could impact electrical systems across the globe.  Already this year Bob Routledge, from the US Space Weather Prediction Centre in Boulder, Colorado, says long-haul flights crossing over the arctic have twice had to be re-routed to avoid potential disaster.

HD 189733b orbits the star HD 189733A, which lies 63 light-years distant in the constellation of Vulpecula. The findings will be published in an upcoming issue of Astronomy & Astrophysics.