An international team from the Institut d'Astrophysique de Paris (CNRS/UPMC) and the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG(1) -- CNRS/Université Joseph Fourier -- Grenoble 1) has detected meteorological variations in the atmosphere of an exoplanet (a planet outside our own Solar System). The astrophysicists made the discovery while observing the exoplanet HD 189733b with the Hubble space telescope.
This work could widen the scope of climate sciences and meteorology, still confined to studying the weather on planets in our Solar System, and give rise to a new sub-discipline, exo-meteorology. These findings are published in the 28 June 2012 issue of the journal Astronomy & Astrophysics Letters. 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 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 , 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.
(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.
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