One year on this exoplanet lasts only 18 hours

This hot Jupiter type planet makes a full trip around its host star in just 18 hours, giving it the shortest year out of any planet we know so far. However, this may be bad news for the planet itself: the team suspects that this planet is falling into its star.


Too close for comfort


“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,” says lead author Dr. James McCormac from the University of Warwick Department of Physics. “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.


The planet lies around 1000 light-years away from Earth, and was discovered as part of the Next-Generation Transit Survey (NGTS) exoplanet survey using the transit method. Basically, it was detected by analyzing the dips in brightness it causes while passing in front of its host star.


It was immediately apparent that this planet was not like most others; it transited in front of the star way too often.


“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,” explains McCormac. “Of the hundreds of hot Jupiters currently known there are only seven that have an orbital period of less than one day.”


NGTS-10b is very close to its star, orbiting only two times the diameter of the star away from its surface. In our solar system, the team explains, this would make it around 27 times closer to it than Mercury is to our Sun. This would put NGTS-10b dangerously close to being ripped apart by the star’s tidal (gravitational) forces.


Temperatures on its surface are likely around 1000 degrees Celsius on average, they add, since the host star is only around 70% as big as the Sun in diameter and its surface is 1000 degrees Celsius cooler. NGTS-10b itself is around one-fifth larger than Jupiter, estimated to be over twice its mass and likely tidally locked to the star.


Massive planets typically form some distance away from their stars, and can then migrate either while they’re still forming or after they mature. This makes NGTS-10b particularly useful, as the team plans to continue observing it and determine whether it will continue falling into the star — potentially telling us more about how hot Jupiters form.


“It’s thought that these ultra-short planets migrate in from the outer reaches of their solar systems and are eventually consumed or disrupted by the star,” explains co-author Dr. David Brown.

“We are either very lucky to catch them in this short period orbit, or the processes by which the planet migrates into the star are less efficient than we imagine, in which case it can live in this configuration for a longer period of time.”


The paper “NGTS-10b: the shortest period hot Jupiter yet discovered” has been published in the journal Monthly Notices of the Royal Astronomical Society.

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