This Massive Planet Shouldn't Exist

fahrbot-bot shares a report from Gizmodo: Scientists have spotted an unusually large exoplanet in orbit around b Centauri, a massive two-star system that is visible to the unaided eye. With a combined weight of roughly 10 Suns, it's now the heaviest star system known to host a planet. The details of this discovery were published today in Nature. The newly discovered planet, called 'b Cen (AB)b,' is likely a gas giant and is heavier than 10 Jupiters combined, making it one of the most massive planets ever discovered. It orbits the b Centauri binary system, which is located 325 light-years from Earth and has a combined mass of nearly 10 Suns. At 52 billion miles from its host stars, this planet has one of the widest orbits ever detected. By comparison, Pluto orbits the Sun at around 3.3 billion miles, so yeah, that's an unbelievable separation. Until now, planets had not been found in orbit around star systems weighing more than three solar masses. Astronomers didn't think planets could form around systems like this, so it's forcing a major rethink of what's possible in terms of planetary architectures and the conditions under which planets can form.

That a planet exists in this star system is indeed surprising. Young stars have protoplanetary disks around them, from which planets eventually emerge. A hot star system like b Centauri, however, is not supposed to be conducive to planetary formation, owing to tremendous amounts of ultraviolet and X-ray radiation. This high-energy radiation 'tends to destroy the disks in a very short time,' and it was 'thought that this wouldn't give planets enough time to form in the disk before it disappeared,' [said Markus Janson, an astronomer at Stockholm University and the first author of the study]. Yet there it is -- a full fledged planet around the b Centauri system. A neat observation is how the ratio between the masses of the star system and its planet closely matches that of our Sun and Jupiter. But that's where the comparison ends, as the scale of b Centauri is far vaster, as the planet is 10 times the mass of Jupiter and with an orbit that's 100 times wider.

From an astrobiological perspective, Janson added that b Centauri is 'possibly one of the worst places in the galaxy to host life.' Together, the binary pair spew enormous amounts of UV and X-ray radiation, 'which would sterilize any surface that is exposed to it,' so 'life on any surface in the system is certainly not very likely.' Still, Janson did not rule out the possibility that life could exist in subterranean oceans, matching ongoing speculation about basic life existing on Jupiter's moon Europa or Saturn's moon Enceladus.

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