Researchers have identified a new exoplanet, TOI-3261b, orbiting the inactive main-sequence star TOI-3261, located 300 parsecs (978.5 light-years) away in the constellation Hydrus. This exoplanet is notable for its size, with a radius of 3.82 Earth radii and a mass of 30.3 Earth masses, more than twice the median mass of Neptune-sized planets on longer orbits.
The discovery was made by astronomer Emma Nabbie from the University of Southern Queensland and her team, utilizing data from NASA's Transiting Exoplanet Survey Satellite (TESS), the Las Cumbres Observatory Global Telescope, and the ESPRESSO and HARPS instruments. The findings place TOI-3261b in the 'hot Neptune desert,' a category of planets characterized by their scarcity.
TOI-3261b completes an orbit around its star every 21 hours, joining an exclusive group of ultra-short-period hot Neptunes, which includes only three others: LTT-9779b, TOI-849b, and TOI-332b. The researchers suggest that TOI-3261b serves as an ideal candidate for testing new models of planet formation.
Hot Neptunes like TOI-3261b are rare, primarily due to the challenges of retaining a thick gaseous atmosphere in close proximity to their stars. The gravitational forces and energy emissions from the star can strip away gas layers, leading to significant mass loss. The TOI-3261 system is estimated to be about 6.5 billion years old, and the planet likely began as a larger gas giant before losing mass through processes such as photoevaporation and tidal stripping.
The remaining atmosphere of TOI-3261b, which is approximately twice as dense as Neptune, indicates that lighter atmospheric components have been lost over time, leaving behind heavier elements. Further atmospheric analysis is anticipated, which may provide insights into the planet's formation history and its place within the hot Neptune desert.