No Rain on Nearby Exoplanet

An international team of astrophysicists using NASA’s Hubble Space Telescope has detected meteorological variations in the atmosphere of the exoplanet HD 189733b.

HD 189733 system has a Jupiter-class planet in a tight orbit, where methane and water vapor have been detected by filtering the star’s light through the planet’s atmosphere (NASA / ESA / G. Bacon / Space Telescope Science Institute)

Located 63 light years from Earth, HD 189733b is a gas giant planet with a hazy atmosphere mainly composed of hydrogen. Due to close proximity to its star – about 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 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, the team revealed meteorological variations in an exoplanet’s atmosphere. The discovery was described in a paper in the journal Astronomy & Astrophysics Letters.

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.

This research 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.

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Bibliographic information: Lecavelier des Etangs A et al. 2012. Temporal variations in the evaporating atmosphere of the exoplanet HD189733b. Astronomy & Astrophysics Letters 543, L4; doi: 10.1051/0004-6361/201219363