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Star fries planet with X-rays
Posted: 14 September 2011

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New data from the Chandra X-ray Observatory and ESO's Very Large Telescope find that a planet discovered in 2008 by CoRoT is being eroded away by an intense stream of X-rays from its host star.

The system, which comprises a bloated three-Jupiter mass planet orbiting its star at a distance roughly ten times the Earth-Moon separation, lies 880 light years away and was first detected by the Convection, Rotation and planetary Transits satellite, CoRoT. New data from Chandra and the VLT reveal that high-energy radiation is evaporating about five million tons of matter from the planet every second. While this may seem a lot, it is equivalent to a loss of just 0.073 Jupiter masses per billion years.

A star is blasting a planet with intense X-rays, but the planet itself could be responsible for the star's activity. Image: NASA/CXC/M.Weiss.

"Complete evaporation would take longer than the star's lifetime," comments lead scientist Sebastian Schroeter of the University of Hamburg in Germany, on the fate of the planet. "However, we would expect the planet and its host star to be gravitationally interacting – this could indeed lead to a further decay of the planet's orbit, but we do not have any observational evidence for such a process."

The system is estimated to be 100-300 million years old, that is, the star is fully formed. But the observation of such intense X-ray activity produced by the star's magnetic fields is more typical of younger stars, so the scientists suspect that the close proximity of the planet may be speeding up the star’s rotation, keeping its magnetic fields active.

“If it wasn’t for the planet, this star might have left behind the volatility of its youth millions of years ago,” adds co-author Stefan Czesla, also from the University of Hamburg.

X-Ray and optical/infrared image of CoRoT-2a and its close companion star. Image: X-ray: NASA/CXC/Univ of Hamburg/S.Schršter et al; Optical: NASA/NSF/IPAC-Caltech/UMass/2MASS, UNC/CTIO/PROMPT.

Support for this idea comes from the detection of a potential companion star orbiting Corot-2a at a thousand times greater than the separation of the Earth and Sun. The star is not seen in X-rays, which suggests the absence of a planet that would otherwise be keeping it active.

"Assuming that the distant companion star is gravitationally bound and has the same age as CoRoT-2a – both stars should have formed together – we would expect the companion to be X-ray active too, but this is not the case," Schroeter tells Astronomy Now. "One could say, the planet kept its star from maturing. Following this argument, without its planet, CoRoT-2a would be much less magnetically active, perhaps rotating slower and would be X-ray dark as is its companion star."

The study is published in the August issue of Astronomy and Astrophysics.

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