Over 4000 exoplanets have been discovered since the first one in 1995, but the vast majority of them orbit their stars with relatively short periods of revolution. But five new planets have been discovered with periods of revolution between 15.6 and 40.4 years, with masses ranging approximately from 3 to 27 times that of Jupiter. A new study using the EULER telescope at the La Silla Observatory in Chile increases the list of 26 planets with a rotation period greater than 15 years.
To confirm the presence of a planet, it is necessary to wait until it has made one or more revolutions around its star. This can take from a few days for the closest to the star to decades for the furthest away: Jupiter for example takes 11 years to go around the sun. Only a telescope dedicated to the search for exoplanets can carry out such measurements over such long periods of time, which is the case of the EULER telescope.
These planets with long periods of revolution are of particular interest to astronomers because they are part of a poorly known but unavoidable population to explain the formation and evolution of planets.
“It took 20 years and many more observers,” says Emily Rickman, first author of the study and a researcher in the Astronomy Department of the University of Geneva. “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.”
Planets with long periods of revolution are of great interest to astronomers. Being farther away from their stars, they can be observed using direct imaging techniques. To date, almost all planets have been discovered using the two main indirect methods: radial velocities, which measure the gravitational influence of a planet on its star, and transits, which detect the mini eclipse caused by a planet passing in front of its star.
Planets directly observed
The EULER telescope is mainly dedicated to the study of exoplanets. Since its commissioning in 1998, it has been equipped with the CORALIE spectrograph, which allows astronomers to measure radial velocities with an accuracy of a few meters per second for the detection of planets with a mass as small as Neptune’s.
“As early as 1998, a planetary monitoring program was set up and carried out scrupulously by the many UNIGE observers who took turn every two weeks in La Silla for 20 years,” says Emily Rickman.
Glowing a dark magenta, exoplanet GJ 504b shown at the top of the page weighs in with about four times Jupiter’s mass. NASA’s Goddard Space Flight Center/S. Wiessinger
The Daily Galaxy, Sam Cabot via Geneva University (UNIGE)