Five planets revealed after 20 years of observation

More than 4000 exoplanets have been discovered since the first in 1995, but the vast majority of them revolve around their stars with relatively short periods of revolution. Indeed, to confirm the presence of a planet, we must wait until it has made one or more revolutions around its star. This can take from a few days to the nearest star to decades to the farthest: Jupiter, for example, takes 11 years to go around the sun. Only a telescope dedicated to the search for exoplanets can perform such measurements over such long periods, as in the case of the EULER telescope of the University of Geneva (UNIGE), Switzerland, located at the University of Geneva. observatory of Silla in Chile. These planets with long periods of revolution are of particular interest to astronomers because they are part of a poorly known but inevitable population to explain the formation and evolution of planets. An article published by the journal Astronomy and astrophysics.

"It has taken 20 years and many more observers," said Emily Rickman, first author of the study and researcher at the Department of Astronomy of the UNIGE Faculty of Science. "This result would have been impossible without the availability and reliability of the CORALIE spectrograph installed on the EULER telescope, a unique instrument in the world."

Since 1995, the year of the discovery of the first exoplanet, about 4,000 planets have been discovered. The vast majority of them are gigantic planets close to their stars, which are the easiest to detect using current technology. However, planets with long periods of revolution are of great interest to astronomers. Being farther from their stars, they can be observed with the help of direct imaging techniques. Indeed, to date, almost all the planets have been discovered according to the two main indirect methods: radial velocities, which measure the gravitational influence of a planet on its star, and transits, which detect the induced mini-eclipse by a planet passing in front of its star.

Planets observed directly

The EULER telescope is mainly dedicated to the study of exoplanets. Since it was commissioned in 1998, it has been equipped with the CORALIE spectrograph, which allows astronomers to measure radial velocities with a precision of a few meters per second for the detection of planets as small as Neptune.

"By 1998, a global surveillance program had been implemented and scrupulously executed by the many observers from UNIGE who took turns every two weeks in La Silla for 20 years," says Rickman. The result is remarkable: five new planets have been discovered and the orbits of four others have been precisely defined. All these planets have periods of revolution between 15.6 and 40.4 years, with masses approximately 3 to 27 times higher than those of Jupiter. This study helps to increase the list of 26 planets with a rotation period greater than 15 years, "but it provides us first and foremost new targets for direct imaging," concludes the researcher from Geneva.