Out of the few thousand known exoplanets, astronomers have only been able to directly image a handful. Each and every one of them has been quite unique so far so it was quite a shock to discover two nearly identical exoplanets in two different star systems.
As reported in an upcoming issue of The Astronomical Journal, researchers have discovered that exoplanet 2MASS 0249 c is like a twin to exoplanet beta Pictoris b. They have the same brightness and the same light spectrum. They also have the same mass, roughly 13 times the mass of Jupiter. The paper is currently available on arXiv.
There is another peculiar fact about these two planets. The researchers believe the stars they orbit come from the same stellar nursery. Stars form in groups from giant clouds of gas and dust stretching for many light-years. Stars formed this way don’t have to be similar at all and this is, in fact, the case for these two planets. Beta Pictoris b orbits a star 10 times brighter than our Sun while 2MASS 0249 c orbits a pair of brown dwarfs, 2,000 times fainter than the Sun.
This difference is actually very important. The two would-be twin planets have different stars and different origins. Beta Pictoris b grew near its star, forming from the accumulation of gas from the protoplanetary disk, which is how we expect the gas giant planets in the Solar System to have formed. 2MASS 0249 c formed 300 billion kilometers from its stars, and it likely formed directly from the stellar nursery.
“To date, exoplanets found by direct imaging have basically been individuals, each distinct from the other in their appearance and age. Finding two exoplanets with almost identical appearances and yet having formed so differently opens a new window for understanding these objects,” co-author Michael Liu, from the University of Hawai`i Institute for Astronomy, said in a statement.
“2MASS 0249 c and beta Pictoris b show us that nature has more than one way to make very similar looking exoplanets,” co-author Kaitlin Kratter, an astronomer at the University of Arizona, added. "They’re both considered exoplanets, but 2MASS 0249 c illustrates that such a simple classification can obscure a complicated reality.”
The last two decades have seen our view on planetary formation be challenged and shift as more and more planetary objects have been discovered beyond the Solar System.