The planet – called Gaia-4b – has a mass 12 times heavier than Jupiter, and it uses 570 days to orbit it's star. Gaia-4b is the first planet detected by the European Space Agency’s Gaia spacecraft using the “astrometric” technique and whose orbit has been independently confirmed with spectroscopic measurements. The planet is one of the most massive planets known to orbit a low-mass star. Gaia is expected to be able to detect thousands of exoplanets around nearby stars through its precise monitoring of the positions and motions of stars in the galaxy.

This method for detecting planets is called the astrometric technique, and it relies on detecting tiny changes in a star’s position on the sky as it is tugged by the gravity of an orbiting planet.

The observations with Gaia of the tiny movements of the host star against the sky background has been followed up by observations with the technique of spectroscopy. “Together, the astrometric technique and the spectroscopic technique can fully characterize the orbital parameters of a planet,” says coauthor Marcus Marcussen, a PhD student at Aarhus University in Denmark. “Not only does this give a wealth of information of how these planets might have formed and evolved, but also enables us to clearly visualize the orbits as they are viewed on the plane of the sky.”

Marcus has observed the exoplanet with the FIES Spectrograph on the 2.6m Nordic Optical Telescope at La Palma in the Canary Islands and managed by Aarhus University.

The paper in Astronomy & Astrophysics is titeled 'Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars' and a draft version can be found here.

(this text is adapted from a press release from The Netherlands Research School for Astronomy (NOVA)).