A gas giant exoplanet has been found that orbits around its star once every 16 hours, and it is being pulled towards its star faster than any other known world.
TOI-2109b is a planet five times the mass of Jupiter, located about 850 light years from Earth. It has the shortest orbital period of any gas giant known, surpassing . “It’s a new record-holder,” says Ian Wong at the Massachusetts Institute of Technology, who led the team that discovered the planet using NASA’s Transiting Exoplanet Survey Satellite (TESS).
The planet, which has a diameter about 35 per cent larger than Jupiter, is located about 20 times closer to its star than Mercury is to our own sun. That extreme proximity makes it the second hottest planet ever found – a so-called ultra-hot Jupiter – with a day-side temperature of more than 3000°C. Only one other world, at around 4300°C, is known to be hotter.
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TOI-2109b is orbiting so near to its star that it is being pulled into it faster than any other planet we have discovered to date. “When a planet is so close, the star exerts a tidal force on the planet’s atmosphere,” says Wong. Its orbital period is thought to be reducing by nearly a second each year. “If you wait 10 million years, this planet will probably have been swallowed up by the star,” says Wong.
The high temperature of the planet, coupled with the brightness of its host star, should make this a prime target for further study. at the University of Leicester in the UK says scientists will be able to observe the reflected light of the planet to see what is in its atmosphere. “It’s a really exciting discovery,” she says. “We’ll be able to see if there’s any water there, any iron, all sorts of stuff. We can’t do these techniques for very faint planets.”
While hundreds of hot Jupiters have been found in our galaxy, how they end up in these tight orbits isn’t entirely clear. They probably form much further out from their star before migrating inwards, says Lars Buchhave at the Technical University of Denmark, a co-author of the study, but the exact process is uncertain. “They’re kind of oddballs,” he says. “Hot Jupiters were not at all expected.”
The Astronomical Journal
