Paris, 28 June 2012
Located 63 light years (600 000 billion km) from Earth, HD 189733b is a gas giant planet with a hazy atmosphere mainly composed of hydrogen (H2). Due to close proximity to its star (1/30th of the distance from the Earth to the Sun), its upper atmosphere receives a huge amount of energy in the form of ultraviolet and X-ray radiation.
The researchers initially observed the star in order to confirm a result obtained in 2003 with the Hubble telescope for another exoplanet, HD 209458b (2), located in a different planetary system. They discovered that the hydrogen making up the topmost layer of the planet's atmosphere was spreading out in a huge plume, providing evidence that its atmosphere was evaporating into space.
Recent observations of HD 189733b confirm the existence of this phenomenon on another exoplanet. More importantly, they reveal meteorological variations in an exoplanet's atmosphere.
In fact, the researchers observed HD 189733b on two occasions. In April 2010 they saw nothing unusual. However, in September 2011 they detected a huge cloud of gas six times larger than the planet itself. This shows that the state of the atmosphere had changed in the meantime, and that the scientists had found a meteorological difference on HD 189733b.
What caused the change? What is the effect of the star and its radiation on the weather in the exoplanet's upper atmosphere? To find out more, three new observations are already planned.
© NASA, ESA, L. Calçada
"A stellar flare blasting an exoplanet": this artist's impression shows exoplanet HD HD189733b transiting in front of its star. The Hubble Space Telescope observed the transit in September 2010 and April 2011. The April 2011 observation took place just after a strong stellar flare (shown in the image) observed in the X-ray waveband by the Swift telescope. After the flare, the Hubble observations showed that the planet was losing over 1000 tonnes of gas per second.
(In this image, the star's surface is inspired by observations of the Sun by the Solar Dynamics Observatory spacecraft.)
(1) IPAG is a laboratory belonging to the Observatoire des Sciences de l'Univers de Grenoble (OSUG).
(2) “An extended upper atmosphere around the extra-solar planet HD 209458b”; A. Vidal-Madjar et co.; Nature; 13 March 2003.
Temporal variations in the evaporating atmosphere of the exoplanet HD189733b
Lecavelier des Etangs, V. Bourrier, P. J. Wheatley, H. Dupuy, D. Ehrenreich, A. Vidal-Madjar, G. Hébrard, G. E. Ballester, J.-M. Désert, R. Ferlet, and D. K. Sing
Astronomy & Astrophysics Letters, 28 June 2012.
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