Astronomers find the doppelganger of a famous exoplanet

When it comes to extrasolar planets, appearances can be misleading. Astronomers have imagined a new planet, and it seems almost identical to one of the best studied gaseous planets. But this doppelganger differs in a very important way: its origin.

"We found a gas giant planet that is a virtual twin of a previously known planet, but it looks like two objects formed in different ways," Trent Dupuy, astronomer at the Gemini Observatory and leader from the study

Emerging from stellar nurseries of gas and dust, stars are born like kittens in a litter, in clusters and inevitably move away from their place of birth. These litters include stars that vary widely, ranging from small runtes unable to generate their own energy (called brown dwarfs) to massive stars that end their lives with supernova explosions. In the midst of this turmoil, planets are forming around these new stars. And once the stellar nursery exhausts its gas, the stars (with their planets) leave their place of birth and roam freely in the galaxy. Because of this exodus, astronomers believe that there should be planets born at the same time from the same stellar nursery, but are stars in orbit that have moved away from each other over the ages, as brothers and sisters lost for a long time

. The exoplanets discovered by direct imaging are essentially individuals, distinct from one another by their appearance and their age: finding two exoplanets with almost identical appearances and forming so differently opens a new window to understand these objects, "says Michael Liu, astronomer at the Institute of Astronomy of the University of Hawaii, and collaborator at this work.

Dupuy, Liu and their collaborators identified the first case of such a planetary doppelganger.An object is known for a long time: the beta planet of 13-Jupiter Pictoris b, one of the first planets discovered by direct imaging, in 2009. The new object, dubbed 2MASS 0249 c, has the same mass, the same brightness and the same beta spectrum Pictoris B.

After discovering this object with the Canada-France-Hawaii telescope (CFHT), Dupuy and his collaborators then determined that 2MASS 0249 c and beta Pictoris b were born in the same stellar nursery. On the surface, this makes the two objects not only look-alikes but authentic brothers and sisters.

However, planets have very different life situations, namely the types of stars that they orbit. The host of Beta Pictoris b is a star 10 times brighter than the Sun, while 2MASS 0249 c orbiting a pair of brown dwarfs 2000 times weaker than the Sun. In addition, the beta Pictoris b is relatively close to its host, about 9 astronomical units (AU, the distance from the Earth to the Sun), while 2MASS 0249 c is 2000 AU of its binary host.

These radically different arrangements suggest that the education of the planets did not resemble each other at all. The traditional image of the gaseous giant formation, where the planets begin as small rocky nuclei around their host star and grow by accumulating gas from the star disk, probably created beta Pictoris b. In contrast, the host of 2MASS 0249 c did not have enough disk to make a gaseous giant, so the planet probably was formed by directly accumulating gas from the stellar nursery of 39; origin. "2MASS 0249c and Beta Pictoris B show us that nature has more of a way to make very similar exoplanets," says Kaitlin Kratter, an astronomer at the University of Arizona and a collaborator at the University of Arizona. job. "The Pictoris B beta is probably formed like most gaseous giants, starting with tiny grains of dust, while 2MASS 0249 c looks like an underweight brown dwarf, formed by the collapse of 2MASS 0249 c illustrates that such a simple classification can obscure a complicated reality. "

The team first identified 2MASS 0249 c using images from CFHT, and their repeated observations revealed that this object is in orbit at a great distance from its host. The system belongs to the group in motion beta Pictoris, a widely dispersed star set named for its famous star of hosting in planet. The observations of the team at W.M. Keck observatory determined that the host is actually a closely separated pair of brown dwarfs. So, in total, the 2MASS 0249 system includes two brown dwarfs and a giant gas planet. The 2MASS 0249 c tracking spectroscopy with the NASA infrared telescope facility and the 3.5 meter telescope of the Astrophysical Research Consortium at the Apache Point Observatory have demonstrated that it shares a remarkable resemblance to the beta Pictoris B.

The 2MASS 0249 system is an attractive target for future studies. The most directly imaged planets are very close to their host stars, preventing detailed studies of the planets due to the bright light of the stars. On the other hand, the very large separation of 2MASS 0249c from its host binary will make measurements of properties such as its surface and composition much easier, which will allow a better understanding of the characteristics and origins of giant gas planets

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This work has been published in ArXiv and is accepted for publication in the Astronomical Journal .

This work was supported by the National Science Foundation under Grant No. AST-1518339.