Planet Hunter Corot Launched
In our own solar system, we can already see small planets like Mars with the naked eye. With the European Corot space telescope, terrestrial celestial bodies can finally be detected elsewhere - using the tiniest changes in brightness.
Astronomers have discovered an average of 25 new planets a year since 1995, when Michel Mayor and Didier Queloz of the Geneva Observatory were able to prove the existence of such an "exoplanet" for the first time. They concluded from the periodic wobble of a star that it must have a companion with which it orbits around a common center.
However, the planets found using this method are mostly very massive gas giants similar to Jupiter, which orbit their central star in a very narrow orbit and are heated up considerably by it. Earth-like planets, on the other hand, are too light to be detectable with the best tools of the exoplanet finder.
The new Corot (pronounced "Koroh") space telescope, which has just been launched on board a Soyuz 2 rocket from the Baikonur Cosmodrome in Kazakhstan, is intended to prove that there are also planets similar to the Earth outside the solar system All started. Equipped with a highly sensitive camera and a 27-centimetre reflecting telescope, Corot will be on the lookout for telltale fluctuations in the brightness of distant stars on its 900-kilometer orbit. Astronomers interpret certain changes in light intensity as a so-called transit - as a brief solar eclipse triggered by the passing of a star planets in front of its sun.
Corot can even measure the minimal light attenuation caused by the small earth-like planets and thus provide indirect evidence of their existence. What's more, the degree of change also provides information about the size of the planet, repeated observations even allow conclusions to be drawn about its mass.
However, despite all the measuring accuracy, this method also requires a good deal of luck. First, the possibility of a transit exists only if a planet's orbit happens to be exactly between the telescope and its star, and second, the longer its orbit, the rarer - and therefore less likely to be observed - its passage. The operators of the telescope - the French space agency CNES in cooperation with ESA and other European partners - therefore assume that most of the planets that Corot will discover during his more than two-year mission will also be "hot Jupiters".
How many Earth-like rocky planets Corot can observe ultimately depends on whether they are the rule or the exception among the celestial bodies. With a total of five different regions of the sky, each with 12,000 stars, which are to be systematically surveyed with the telescope, the probability should be high enough to find at least tens of specimens of the hitherto undiscovered genus.
Besides finding planets using the transit method, Corot (Convection Rotation and Planetary T ransits), as the name suggests, has yet another task to perform, which must be accomplished with the same technology as that used to capture minute variations in brightness: even when there are no planets orbiting stars, their brightness varies as a result of seismic waves blasting their interiors run through. By analyzing these waves, scientists hope to gain insights into the composition and structure of stars. The data that Corot will deliver will then be related to comparable measurements of the Esa satellite Soho on the sun.