Astronomers discover a massive super-Jupiter hiding around a nearby star

In the last decade, astronomers on Earth have thought of Beta Pictoris b a solitary exoplanet gravitating around a huge dusty disc around the star Beta Pictoris. The planet, a super-Jupiter about 13 times larger than our Jupiter, is the only known planet in the young planetary system located about 63 light-years from Earth for 11 years. That was until today.

A new study, published Monday in the journal Nature Astronomy, reveals a second planet of the system Beta Pictoris, Beta Pictoris c. The discovery of the planet, another super-Jupiter representing about nine times the mass of Jupiter, throws a cosmic key into our current understanding of the well-studied but largely mysterious system of the Beta Pictoris system. The system is somewhat famous in the world of astronomy because it is barely 23 million years old and is surrounded by a disk of rock and ice, which allows researchers to discover To study how planetary systems are formed and to shape these discs.

Beta Pictoris was discovered by the same team responsible for the discovery of Beta Pictoris b more than ten years ago, led by the French astronomer Anne-Marie Lagrange, who has been studying the system for more than 30 years. This time, the hunt was a little more indirect.

To search for planets outside our solar system, astronomers use a multitude of different methods. One of the least favorable looking planets is called "direct imaging". The method can detect a planet by seeing the light it reflects from its host star, but most of the time, it is so bright that we can not distinguish the dim light it releases. Fortunately for Lagrange and his colleagues, Beta Pictoris b, which is about the same distance from its star as Saturn from our sun, was found in this way after having carefully studied the data of the Very Large Telescope of Chile.

A measure of "radial velocity" examines the host star looking for small perturbations of its orbit caused by other huge cosmic bodies. Astronomers can measure these disturbances and determine what causes them by measuring the light reaching the Earth. Each year, radial velocity measurements detect dozens of exoplanets, but they are not as effective at tracking distant worlds as the NASA Kepler or TESS telescope.

Although Lagrange and other astronomers focused on the star system for three decades, they were persuaded to host only one planet. Fortunately, Beta Pictoris c could be detected using radial velocity measurements. It was not easy.

"We monitored the radial velocities of Beta Pictoris (which is really complicated because of the fast rotation of the star) and analyzed the data (which was also very complicated because of the pulsation of the star ), "said Lagrange by e-mail.

A specialized instrument installed at the La Silla Chilean Observatory, the HARPS (High Precision Radial Velocity Radial Planetarium), has provided 15 years of data to locate the new planet. The team said Beta Pictoris c was about 2.7 AU from its star. For comparison, this places it approximately in the same position as the asteroid belt of the solar system.

If the signal they detected is another planet, it would be the first time that a multi-planet system has been detected using direct imaging and indirect detection methods. . Lagrange says that the discovery shows that the planetary systems can be incredibly gigantic, this one now representing about 20 times the mass of Jupiter in only two worlds. And if there are other smaller planets in the system, the huge Beta Pictoris probably also influences their orbit.

Lagrange says she will continue to study Beta Pictoris and search for other planets, which could help explain some of the more difficult questions posed by her latest discovery. The hypothesis is that Beta Pictoris c could also transit in front of the star (view of the Earth), which would allow the team to characterize its size, its atmosphere and determine if it has moons. or rings.

Updated 17:13 PT