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A Distant Planet Whose Atmosphere Was Blasted Away by Solar Flares

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You might think our own sun is turbulent — but it turns out we've got it easy. Astronomers have found a gas giant, 60 light years away from Earth, that's been hit with a violent flare from its star, blasting it with an intense wave of X-ray radiation. Because the exoplanet is so close to its sun, the radiation causes its atmosphere to evaporate into space at a rate of 1,000 tons per second.

Astronomer Alain Lecavelier des Etangs and his team at the French National Centre for Scientific Research were able to pick up on the dramatic events by using the Hubble Space Telescope and comparing data recorded from 2010 and 2011. Because the planet was silhouetted against its parent star, they were able to use the transit method of observation to make the discovery. When the exoplanet was backlit in this way, its atmosphere imprinted its unique chemical signature on the starlight, allowing astronomers to get a sense of what was going on.


The exoplanet, called HD 189733b, is a huge gas giant that's similar to Jupiter, but extremely close to its sun — a mere one-thirtieth the distance that we are from our Sun (about 5 million kilometers). And even though its sun is smaller and cooler than ours, this planet's climate is exceptionally hot — above 1,000 degrees Celsius. Its upper atmosphere is being constantly bombarded with extreme-ultraviolet and X-ray radiation, making it an amazing object for study purposes.


The discovery marks the first time that astronomers have measured such dramatic changes in the atmospheric conditions of a distant planet.

Despite the fact that the planet has such a hot atmosphere to begin with, it's not hot enough to cause the evaporation. Instead, the scientists believe that the evaporation is driven by intense X-rays and extreme-ultraviolet radiation from its parent star. Given its proximity to the sun, and considering that the star's energetic output is 20 times more powerful than our own, this planet probably suffers an X-ray dose 3 million times higher than the Earth.

The researchers' suspicions were backed up by data from the Swift satellite, which, unlike Hubble, can observe the star's X-Rays. A few hours before Hubble observed the planet for a second time, Swift detected a powerful flash of radiation coming from the surface of the star, which for a brief time became four times brighter in X-rays.

In a press release, team member Peter Wheatley noted that, "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."


When X-Rays are this intense, they heat the gases in the upper atmosphere to tens of thousands of degrees – hot enough to escape the gravitational pull of the gas giant. Interestingly, the same sort of effect occurs here on Earth when a space weather event such as a solar flare hits the Earth's ionosphere, disrupting communications.

Not content to posit just one theory for the observed phenomenon, the researchers also speculated that it may be that the baseline level of X-ray emissions from the star increased between 2010 and 2011, in a seasonal process similar to the Sun's 11-year sunspot cycle.


Theories aside, what the researchers can be sure about is that the gas giant was hit by a stellar flare, and that the atmosphere's rate of evaporation has skyrocketed. The team plans on making future observations with Hubble and ESA's XMM-Newton X-ray space telescope.

This kind of research is relevant for not just the study of gas giants, but for rock "super-Earths" as well. Astronomers theorize that even these planets are susceptible to similar solar blasts, causing the complete evaporation of their atmospheres.


In addition to the image above, Hubble has provided a number of video interpretations of the phenomenon.

Be sure to read the entire study.

Via Science2.0. Images via Hubble Space Telescope.