Ultra-light planet found outside Solar System
The European Southern Observatory (ESO) has discovered what appears to be the lightest planet ever to be directly observed outside of our Solar System.
Astronomers made the discovery using the Very Large Telescope (VLT), located in Chile, which captured the faint object moving near a bright star about 300 light years from Earth. The possible planet has an estimated mass that is four-to-five times that of Jupiter.
Dubbed HD95086b, the planet appears in ESO’s observations as a faint but clear dot close to the star HD95086, which astronomers consider a fairly young star – about 10 to 17 million years old.
The star itself is a little more massive than the Sun and is surrounded by a debris disc, a disk of dust and debris orbiting a star. It was those properties that allowed ESO astronomers to identify the star as an ideal candidate to harbor young massive planets. Astronomers believe the new exo-planet was probably formed within that gaseous and dusty debris disc.
“Its current location raises questions about its formation process. It either grew by assembling the rocks that form the solid core and then slowly accumulated gas from the environment to form the heavy atmosphere, or started forming from a gaseous clump that arose from gravitational instabilities in the disc,” said Anne-Marie Lagrange, a member of the team that made the discovery. “Interactions between the planet and the disc itself or with other planets may have also moved the planet from where it was born.”
Later observations indicated the planetary object moved with the star across the sky, suggesting that it is in orbit with the star.
HD95086b is believed to orbit its young star at a distance of around 56 times the distance from the Earth to the Sun and twice distance between the Sun and Neptune.
Considering the brightness of its star, ESO astronomers estimate the surface temperature of HD95086b is about 700 degrees Celsius.
“This is cool enough for water vapor and possibly methane to exist in its atmosphere. It will be a great object to study with the forthcoming SPHERE instrument on the VLT. Maybe it can also reveal inner planets in the system, if they exist,” said Gaël Chauvin, another member of the team.
Astronomers were able to capture an image of HD95086b, which is unusual. Most exo-planets are too far away to be properly imaged.
Experts usually have to rely on indirect methods to find planets, such as looking for a star to dim slightly which may be caused by a planet crossing in front of it. The ESO says there are only about 12 extra-solar or exo-planets that have been discovered using direct imaging.
“Direct imaging of planets is an extremely challenging technique that requires the most advanced instruments, whether ground-based or in space,” says Julien Rameau of the Institute of Planetology and Astrophysics in Grenoble, France who is first author of the paper announcing the discovery. “Only a few planets have been directly observed so far, making every single discovery an important milestone on the road to understanding giant planets and how they form.”
(VLT image of exoplanet HD 95086b, the blue circle is the size of the orbit of Neptune in the Solar System. Photo credit: ESO/J. Rameau)