Paris Observatory / UFE
Instead of trying to observe an exoplanet directly, we measure the effects it creates on its star :
- The perturbation on the movement of the star can lead to two different types of measurements :
- the perturbation on the relative velocity of the star compared to the Earth, which is measured by spectroscopy. To date, most of the known exoplanets have been discovered with this method. It does not allow us to reach the accuracy necessary for the detection of planets such as the Earth.
- the successive positions of the star over the course of time. This method is more difficult to realize.
- The perturbation of the luminosity of the star (transit), which is the method used by CoRoT.
The star and its planet form a system with a center of mass very close to the star, even in the interior; the star and the planet both move around the barycenter of the system. The movement of the star looks like the head of a hammer thrower. This is a slight periodic movement that we can detect either by measuring the velocity variations compared to the Earth through spectroscopy, or accurately measuring its position relative to nearby stars.