An international team of researchers has discovered an extremely peculiar planetary system, where a warm, massive gas giant planet is orbiting an incredibly fast-spinning star. According to physics, this planet shouldn’t exist. But the planet itself doesn’t care what we think.
There are several oddities about this star, called HIP 65426, and its planet HIP 65426b. The star is twice as massive as the Sun and should form more massive planets than HIP 65426b, which is only between six and 12 times the mass of Jupiter. It is also further away than expected, at almost 100 times the Earth-Sun distance. The star rotates on itself 150 times faster than the Sun and, although it’s just 14 million years old, it doesn’t have a dust disk around it.
"We would expect a planetary system this young to still have a disk of dust, which could show up in observations," lead author of the study Gael Chauvin, from the University of Grenoble and the University of Chile, said in a statement. "HIP 65426 does not have such a disk known for the moment – a first indication that this system doesn't quite fit our classical models of planetary formation."
The research, which is published in Astronomy and Astrophysics, proposes an explanation for the curious system. The planet might have formed with a sibling much closer to the star. The gravitational tug-of-war led HIP 65426b to migrate further out and the other planet to be thrown out of the system.
This is an interesting explanation, but anything more solid will require additional observations and simulations. Regardless, this is an exciting system to study. It’s always great when astronomers discover a system that shouldn’t exist according to current models. We know that the models are approximations and these exceptions tells where we need to look for new answers.
The discovery was possible thanks to the SPHERE instruments on the Very Large Telescope at ESO's Paranal Observatory in Chile. HIP 65426b is the first planet discovered by SPHERE, and since it’s so far away, researchers were able to get direct images of it. They detected the presence of water vapor and reddish clouds.
"Direct images of exoplanets are still very rare, but they contain a wealth of information about planets such as HIP 65426b," co-author and putative father of SPHERE Thomas Henning, from the Max Planck Institute for Astronomy, added. "The analysis of the direct light of the planet allows us to constrain the composition of the planet's atmosphere with great confidence."
HIP 65426b reminds us that although exoplanet discoveries are commonplace, there’s a lot still we don’t know about their formation.