30 May 2008
The missing link between stars and planets?
The discoveries were announced last week at the IAU symposium in Boston, U.S.A., by the COROT science team. The satellite developed and operated by CNES has found 2 new gas giants orbiting very close to their star and with very extensive atmospheres. Such observations are relatively frequent, since more than 300 gas giant exoplanets have already been seen, mainly by ground observatories, since the 1st discovery in 1995.
COROT, which has now been operating for 518 days, began observing its 6th star field on 15 April. Illustration: CNES/D. Ducros.
But it was a new type of object presented at the symposium that raised particular interest and fuelled intense debate among the COROT science team and the 200 astronomers in attendance. Provisionally dubbed CoRoT-exo-3b, this object is something of an oddity. “It’s slightly smaller than Jupiter (0.8 times its radius), but follow-up observations from the ground have pinned it at 20 Jupiter masses. It would appear to be somewhere between a planet and a compact brown dwarf, and is twice as dense as the metal platinum,” explains Olivier Vandermarcq, COROT mission leader at CNES’s Toulouse Space Centre. “It might just be the missing link between stars and planets!”
1: Curve showing variation in star’s brightness during a planetary transit 2: Curve showing variation in brightness of a binary star whose 2 components eclipse each other in turn and reflect the light of their companion. Credit: CNES.
After a series of orbit correction manoeuvres early in April to set it up for subsequent observations, the satellite, which has now been operating for 518 days, began observing its 6th star field on 15 April. This phase will last 5 months, during which COROT will train its sights on no less than 12,000 stars simultaneously.
“Possibly one of the smallest exoplanets yet discovered”
Another important discovery made by COROT is a faint signal just 5/10,000ths as bright as a star, which could indicate the existence of another very small exoplanet. COROT’s measurements are so precise that it is able to detect telluric planets much smaller than gas giants. The satellite uses the transit method (see animations) to detect planets as they pass in front of their parent star and block out part of the light seen by the telescope.
This signal could indicate the existence of an object as small as 1.7 times Earth’s radius. Credit: Observatoire de Paris.
“The radius of this planet could be 1.7 times Earth’s radius,” enthuses Olivier Vandermarcq. “If confirmed by analysis here on Earth, it could be the smallest exoplanet yet discovered!”