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HD 189733 b is an extrasolar planet approximately 63 light-years away from the Solar System in the constellation of Vulpecula. The planet was discovered orbiting the star HD 189733 A on October 5, 2005, when astronomers in France observed the planet transiting across the face of the star. With a mass 13% higher than that of Jupiter, HD 189733 b orbits its host star once every 2.2 days at an orbital speed of 152.5 kilometres per second (341,000 mph), making it a hot Jupiter with poor prospects for extraterrestrial life. Being the closest transiting hot Jupiter to Earth, HD 189733 b is a subject for extensive atmospheric examination. HD 189733 b was the first extrasolar planet for which a thermal map was constructed, to be detected through polarimetry, to have its overall color determined (deep blue), to have a transit detected in X-ray spectrum and to have carbon dioxide detected in its atmosphere.

In July, 2014, NASA announced finding very dry atmospheres on three exoplanets (HD 189733b, HD 209458b, WASP-12b) orbiting Sun-like stars.

This artist�s impression shows the super-Earth exoplanet GJ 1214b passing in front of its faint red parent star. This is the first super-Earth exoplanet to have had its atmosphere analysed. The exoplanet, orbiting a small star only 40 light-years away from us, has a mass about six times that of the Earth. GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes.

This is an artist�s impression of the gas giant exoplanet WASP-121b. The bloated planet is so close to its star that the tidal pull of the star stretches it into an egg shape. The top of the planets atmosphere is heated to a blazing 2500 degrees Celsius, hot enough to boil iron. This is the first planet outside our Solar System where astronomers have found the strongest evidence yet for a stratosphere � a layer of atmosphere in which temperature increases with higher altitudes. The planet is about 900 light-years away.

Astronomers have discovered the second super-Earth exoplanet for which they have determined the mass and radius, giving vital clues about its structure. It is also the first super-Earth where an atmosphere has been found. The exoplanet, orbiting a small star only 40 light-years away from us, opens up dramatic new perspectives in the quest for habitable worlds. The planet, GJ1214b, has a mass about six times that of Earth and its interior is likely to be mostly made of water ice. Its surface appears to be fairly hot and the planet is surrounded by a thick atmosphere, which makes it inhospitable for life as we know it on Earth.

In this week�s issue of Nature, astronomers announce the discovery of a planet around the nearby, low-mass star GJ1214. It is the second time a transiting super-Earth has been detected, after the recent discovery of the planet Corot-7b. A transit occurs when the planets orbit is aligned so that we see it crossing the face of its parent star. The newly discovered planet has a mass about six times that of our terrestrial home and 2.7 times its radius, falling in size between the Earth and the ice giants of the Solar System, Uranus and Neptune.

Although the mass of GJ1214b is similar to that of Corot-7b, its radius is much larger, suggesting that the composition of the two planets must be quite different. While Corot-7b probably has a rocky core and may be covered with lava, astronomers believe that three quarters of GJ1214b is composed of water ice, the rest being made of silicon and iron.

GJ1214b orbits its star once every 38 hours at a distance of only two million kilometres � 70 times closer to its star than the Earth is to the Sun. �Being so close to its host star, the planet must have a surface temperature of about 200 degrees Celsius, too hot for water to be liquid,� says David Charbonneau, lead author of the paper reporting the discovery.

When the astronomers compared the measured radius of GJ1214b with theoretical models of planets, they found that the observed radius exceeds the models� predictions: there is something more than the planet�s solid surface blocking the star�s light � a surrounding atmosphere, 200 km thick. �This atmosphere is much thicker than that of the Earth, so the high pressure and absence of light would rule out life as we know it,� says Charbonneau, �but these conditions are still very interesting, as they could allow for some complex chemistry to take place.�

�Because the planet is too hot to have kept an atmosphere for long, GJ1214b represents the first opportunity to study a newly formed atmosphere enshrouding a world orbiting another star,� adds team member Xavier Bonfils. �Because the planet is so close to us, it will be possible to study its atmosphere even with current facilities.�

The planet was first discovered as a transiting object within the MEarth project, which follows about 2000 low-mass stars to look for transits by exoplanets. To confirm the planetary nature of GJ1214b and to obtain its mass (using the so-called Doppler method), the astronomers needed the full precision of the HARPS spectrograph, attached to ESO�s 3.6-metre telescope at La Silla. An instrument with unrivalled stability and great precision, HARPS is the world�s most successful hunter for small exoplanets.

�This is the second super-Earth exoplanet for which the mass and radius could be obtained, allowing us to determine the density and to infer the inner structure,� adds co-author Stephane Udry. �In both cases, data from HARPS was essential to characterise the planet.�

�The differences in composition between these two planets are relevant to the quest for habitable worlds,� concludes Charbonneau. If super-Earth planets in general are surrounded by an atmosphere similar to that of GJ1214b, they may well be inhospitable to the development of life as we know it on our own planet.