Astronomers Discover Ultrahot Neptune around TOI-3261

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The newly-discovered exoplanet orbits TOI-3261 (also known as TIC 358070912), an inactive main-sequence star located 300 parsecs (978.5 light-years) away in the constellation of Hydrus.

An artist’s concept of the ultrahot-Neptune exoplanet TOI-3261b. Image credit: NASA / JPL-Caltech / K. Miller, Caltech & IPAC.

Named TOI-3261b (TIC 358070912b), the newfound exoplanet has a radius of 3.82 Earth radii.

It has a mass of 30.3 Earth masses — more than twice the median mass of Neptune-sized planets on longer orbits.

To determine these properties, University of Southern Queensland astronomer Emma Nabbie and her colleagues used data from NASA’s Transiting Exoplanet Survey Satellite (TESS), the Las Cumbres Observatory Global Telescope, and the ESPRESSO and HARPS instruments.

“Our measurements placed TOI-3261b squarely in the hot Neptune desert — a category of planets with so few members that their scarcity evokes a deserted landscape,” the astronomers said in a statement.

“This variety of exoplanet is similar to our own Neptune in size and composition, but orbits extremely closely to its star.”

The planet orbits its parent star, TOI-3261, once every 21 hours.

Such a tight orbit earns this planet its place in the exclusive group with, so far, only three other ultra-short-period hot Neptunes: LTT-9779b, TOI-849b and TOI-332b.

“TOI-3261b proves to be an ideal candidate to test new computer models of planet formation,” the researchers said.

“Part of the reason hot Neptunes are so rare is that it is difficult to retain a thick gaseous atmosphere so close to a star.”

“Stars are massive, and so exert a large gravitational force on the things around them, which can strip the layers of gas surrounding a nearby planet.”

“They also emit huge amounts of energy, which blow the gas layers away.”

“Both of these factors mean that hot Neptunes such as TOI-3261b might have started out as much larger, Jupiter-sized planets, and have since lost a large portion of their mass.”

According to the team, the TOI-3261 system is about 6.5 billion years old, and that the planet started out as a much larger gas giant.

“It likely lost mass, however, in two ways: photoevaporation, when energy from the star causes gas particles to dissipate, and tidal stripping, … Read More