Astronomers Discover Exoplanet With The Shortest Orbital Period Yet

Artist's impression of a hot Jupiter close to its star. University of Warwick/Mark Garlick

Astronomers from the University of Warwick have discovered an exoplanet they are calling NGTS-10b. This world has the shortest orbital period of any exoplanet known, completing a full rotation around its star in just 18 hours.

NGTS-10b is located in a stellar system about 100 light-years from Earth. The planet is about 20 percent larger than Jupiter and more than twice as massive. The star has a radius 70 percent of our Sun and is about 1,000°C (1,800°F) cooler. However, the planet is orbiting so close to the star that it will probably be destroyed by it one day. The discovery, reported in the Monthly Notices of the Royal Astronomical Society, was possible thanks to the Next-Generation Transit Survey (NGTS).

“We’re excited to announce the discovery of NGTS-10b, an extremely short period Jupiter-sized planet orbiting a star not too dissimilar from our Sun. We are also pleased that NGTS continues to push the boundaries in ground-based transiting exoplanet science through the discovery of rare classes of exoplanets,” lead author Dr James McCormac, said in a statement.

“Although in theory hot Jupiters with short orbital periods (less than 24 hours) are the easiest to detect due to their large size and frequent transits, they have proven to be extremely rare. Of the hundreds of hot Jupiters currently known there are only seven that have an orbital period of less than one day.”

The planet is close to the distance in which the star would tear it apart, making it a unique object to study. Gas giants such as these don’t form near their star; they either move there early on in the system formation process due to interactions with the disk or they are pushed forward due to interactions with other planets. Future observations might find reveal which of these is the case for NGTS-10.

“Everything that we know about planet formation tells us that planets and stars form at the same time. The best model that we’ve got suggests that the star is about 10 billion years old and we’d assume that the planet is too. Either we are seeing it in the last stages of its life, or somehow it’s able to live here longer than it should,” co-author Dr Daniel Bayliss explained.

The team is planning to observe this distant world with high-precision instruments to track even small changes to its orbit. “Over the next ten years, it might be possible to see this planet spiralling in. We’ll be able to use NGTS to monitor this over a decade. If we could see the orbital period start to decrease and the planet start to spiral in, that would tell us a lot about the structure of the planet that we don’t know yet,” Dr Bayliss concluded.

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