Team finds smallest transiting extrasolar planet ever

Feb 03, 2009

The CoRoT satellite has discovered a planet only twice as large as the Earth orbiting a star slightly smaller than the Sun. It is the smallest extrasolar planet (planet outside our solar system) whose radius has ever been measured. The planet's composition is not yet certain, but it is probably made predominantly of rock and water. It orbits its host star in 20 hours, which is the shortest orbital period of all exoplanets found so far. Astronomers infer its temperature must be so high (over 1000 degrees C) that it should be covered in lava or superheated water vapour.

Most of the 330 or so exoplanets discovered so far are giant planets, primarily composed of gas, like Jupiter and Neptune. This new object, named CoRoT-Exo-7b, is very different. "Finding such a small planet wasn't a complete surprise", says Dr Daniel Rouan, from LESIA in Paris, who announced the discovery today at a conference in Paris. Dr Alain Leger from the Institut d'Astrophysique de Marseille, leader of the discovery paper, explains: "It could be an example of a so-called ocean planet, whose existence was predicted some years ago: a Neptune-like planet, made of ice around a rocky core, drifts so close to its star, the ice the melting to form a fluid envelope."

Such a small planets such as this one is extremely difficult to detect. CoRoT-Exo-7b was found because it passes in front of its host star, causing the star to dim very slightly once per orbit - a so-called transit, which in this case is only 0.03% deep. "We were able to see it with CoRoT because it is in space, with no atmosphere to disturb the measurements or daylight to interrupt them." explains Dr Roi Alonso, from the Laboratoire d'Astrophysique de Marseille.

The team then had to make sure they were not seeing one of many other kinds of objects that can mimic planetary transits, using complementary observations from the ground. This is particularly challenging in the case of such a small planet, as Dr Aigrain from the University of Exeter explains "We ruled out every mimic except for a very improbable, almost perfect chance alignment of three stars. All our data so far is consistent with the transits being caused by a planet of a few Earth masses, though more data are needed for a precise mass estimate."

The discovery of CoRoT-Exo-7b is being announced today at the CoRoT Symposium 2009 in Paris and will be the published in a forthcoming special issue of the journal Astronomy and Astrophysics dedicated to results from CoRoT.

CoRoT - which stands for Convection, Rotation and planetary Transits - was developed by the French Space Agency CNES, with important contributions from Austria, Belgium, Brazil, the European Space Agency, Germany, and Spain. It was designed to detect tiny variations in the luminosity of stars, with two scientific goals: searching for planets orbiting stars other than the Sun, and studying the internal structure of seismology.

This discovery is based on data from the CoRoT satellite and complementary observations made from the European Southern Observatory at Paranal and La Silla (Chile), the 80-cm telescope at the Canary Islands Astrophysics Institute, and the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii (operated by CNRS, CNRC, and University of Hawaii).

Source: University of Exeter

Explore further: A new approach in the search for extraterrestrial intelligence: targeting alien polluters

add to favorites email to friend print save as pdf

Related Stories

The Sloan Digital Sky Survey expands its reach

Jul 16, 2014

The Sloan Digital Sky Survey (SDSS) has launched a major program of three new surveys, adding novel capabilities to expand its census of the Universe into regions it had been unable to explore before.

James Webb and the search for life beyond Earth

Jul 16, 2014

Before the invention of the telescope, before every continent was on a map, even before the revelation that Earth was not the center of the Universe, humans have wondered at the possibility of life beyond ...

Worldwide contest to name exoplanets and host stars

Jul 10, 2014

For the first time, in response to the public's increased interest in being part of discoveries in astronomy, the International Astronomical Union (IAU) is organizing a worldwide contest to give popular names ...

Recommended for you

Satellite galaxies put astronomers in a spin

39 minutes ago

An international team of researchers, led by astronomers at the Observatoire Astronomique de Strasbourg (CNRS/Université de Strasbourg), has studied 380 galaxies and shown that their small satellite galaxies almost always ...

Video: The diversity of habitable zones and the planets

46 minutes ago

The field of exoplanets has rapidly expanded from the exclusivity of exoplanet detection to include exoplanet characterization. A key step towards this characterization is the determination of which planets occupy the Habitable ...

Ultra-deep astrophoto of the Antenna Galaxies

49 minutes ago

You might think the image above of the famous Antenna Galaxies was taken by a large ground-based or even a space telescope. Think again. Amateur astronomer Rolf Wahl Olsen from New Zealand compiled a total ...

The most precise measurement of an alien world's size

2 hours ago

Thanks to NASA's Kepler and Spitzer Space Telescopes, scientists have made the most precise measurement ever of the radius of a planet outside our solar system. The size of the exoplanet, dubbed Kepler-93b, ...

Lives and deaths of sibling stars

Jul 23, 2014

This beautiful star cluster, NGC 3293, is found 8000 light-years from Earth in the constellation of Carina (The Keel). This cluster was first spotted by the French astronomer Nicolas-Louis de Lacaille in ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

3.7 / 5 (3) Feb 03, 2009
Can we get a little more meat here please?

What's the eccentricity, estimated diameter, what's the metalicity of the star it orbits, is it in the goldilocks zone??

ON EDIT: Nevermind, found my own info. For anyone else intrested...