Jupiter is less bright than the Sun times 1milliard

It rains showers of small pebbles condensing like water droplets in the clouds of oxygen and hot gas of the seventh planet recently discovered by the French Corot satellite! This astonishing hypothesis, issued by two American researchers, who have submitted their data in a powerful software, is one of these beautiful surprises are astrophysicists since that they engage in the assault on extrasolar planets. "Because of their cousin with Earth exoplanets offer exciting fields of study to understand our own evolution," says Claire Moutou, one of the specialists of the subject at the CNRS.

Launched in décembre2006, Corot was theoretically completed his work of observation end of December. But his discoveries were such that his mission will be extended for three years. The space telescope was able to find eight planets outside our solar system. The last, Corot - 7B, revealed in February, has just been confirmed as the first Rocky planet with a density close to Earth. "It justifies it only program", slice Didier Queloz, who confirmed its characteristics at the Observatory of Geneva with data collected by the telescope of ESO Harps spectrograph to the Chile.

"So far, it had no idea of the composition of these small planets are found, says Claire Moutou." "Corot - 7B is a case of school."Small, with a diameter of 1.8 times greater that that of the Earth and a mass five times, Corot-7 b is also sufficiently close to its star to have reached a State of synchronous rotation, as is the case for mercury, for example. "It's rock." "It therefore imagine that similar planets, with a mass between 3 and 5 times that of Earth, are also", extrapolates the astrophysicist.

New detection method

Researchers are therefore close the Holy Grail of the sister planet. Among the discovered exoplanets, most of the gas giants, such as Saturn or Jupiter. Only a dozen are telluric planets, whose surface is solid. Their discovery is extremely difficult, because unlike the stars, they do not shine, but reflect the light of the luminary that illuminates. Jupiter is less bright than the Sun times 1milliard. The Earth, 10milliards. "The locate in stellar infinity, it is like posting in Paris to find a shiny worm posed next to a lighthouse of Navy somewhere on the Mediterranean coast," compares Marc Ollivier, astrophysicist at the Institute of space astrophysics. And where to point the instruments

"Observation owes much to intuition," recognizes Magali Deleuil, teacher-researcher at the Astronomical Observatory of Marseille. The first images of extrasolar planets in our Galaxy (less than 6,000 light years) reached scientists in 2008. They remain the exception. With the increased accuracy of observation instruments, a new detection method has emerged: the calculus of variations of the luminous intensity produced by the passage of a planet before the bright disk of its star. At the time, found primarily on the nearby planets of their Sun have a period of rapid rotation (the most important discovery so far is one hundred eleven days). These are hot planets, even at stage magmatic, or even gas.

Kepler and Plato missions

To discover planets more advanced in evolution, scientists now have two new observation missions. The first, Kepler, is American: it will allow to analyze the light from 100 000étoiles in the constellation of Cygnus for four years. Another hope to discover earth binoculars comes from Europe, with the French program Plato, which the European Space Agency (ESA) must determine the financing (between 200 and 300millions of euros) here in a few weeks, for a launch planned in 2017. Its field of investigation will cover 500,000 nearby stars (less), of which planets will be especially analysed by seismology to determine precisely their size, weight and age.

This valuable catalogue of the distant lights will provide the "short list" of the first candidates to direct observations, images, vague but sufficiently precise to give indications of texture, topography or seasonal cycles. That means, it should wait until 2030.