First results

In May 2007, CoRoT already started delivering a set of seismological data springing from the first exploratory phase. They concerned a Sun like star. From an astrophysical point of view they provided nothing revolutionary: one finds in them a range of frequencies analogous to those of our Sun. It is on the technical level that the results stand out: a precision of less than a millionth has been achieved, which is already better than anticipated even though the data were collected over 60 days only and have still to be entirely interpreted. Astrophysicists hope to gain another factor of ten in terms of precision with fully analysed observations taken over 150 consecutive days.

In the coming months, the deliveries of new data should follow one after the other. Once they have been completely cleaned of interferences, the Liège team grouped around Professor Arlette Noels will play a full part in interpreting them. All in all, the observations gathered by CoRoT will provide our team of theorists with several years of work, as it will to other Belgian teams, including that of Professor Conny Aerts at the Catholic University of Leuven, in very close collaboration at the heart of the Belgian Asteroseismology Group, (BAG). But CoRoT is not exclusively dedicated to asteroseismology.

Exoworlds

Since the end of the 1990s the CoRoT mission has seen itself acquire a second project. That period saw the first discoveries of planets orbiting stars other than our Sun. They have been given the name 'exoplanets'. Scientists were aware that beyond its initial seismology tasks, the CoRoT satellite would be capable of detecting a large number of exoplanets through the transit method. What is the principle at work? When a planet orbiting around a star passes in front of the latter's stellar disc it causes a slight partial eclipse of its star and thus a very tiny lowering of its apparent magnitude.

We have been able to observe this phenomenon in our Solar System, during the transit of Mercury in 2003 and that of Venus in 2004. In each case the planet interposed itself between the Sun and the Earth, giving rise to the crossing of a small black disc across the solar disc.

Astronomers expect an exoplanet to reduce the apparent magnitude of its star by 1% if it is a giant Jupiter like planet or by 0.01% in the case of a small Earth. CoRoT has been precisely designed to measure very weak variations in brightness. It is thus natural that the search for exoplanets has been grafted onto its initial mission.

[1] Pierre-Olivier Bourge, Patrick Eggenberger, Mélanie Godart, Andrea Miglio, Josefina Montalban, Olga Moreira, Arlette Noels, Richard Scuflaire, Sylvie Théado, Anne Thoul.