Using NASA‘s TESS (the Transiting Exoplanet Survey Satellite) and observations from ground-based telescopes in Australia, Chile, and South Africa, an international team of scientists discovered an exoplanet of in a scorching close orbit around its host star.
This ‘Hot Neptune,’ named TOI-3261 b, is the fourth object of its kind ever found.
Its discovery could offer insights into how this type of planet forms. Hot Neptunes are so rare that it is difficult to retain a thick gaseous atmosphere so close to a star. Because of its proximity to its star, a large gravitational force on the things around the planet can strip gaseous layers surrounding a nearby planet.
The high-energy emissions from the stars blow away the outer gas layers, shrinking the planet in size. Over time, intense radiation and strong winds from their stars cause these planets to lose significant mass. Hot Neptunes like TOI-3261 b may have originally been much larger, Jupiter-sized planets.
Study portrays the atmosphere of exoplanet ‘hot Neptune’
TOI-3261 b belongs to the “hot Neptune desert,” a rare category of exoplanets characterized by scarcity. These planets are similar in size and composition to Neptune but orbit extremely close to their stars. In the case of TOI-3261 b, its orbit is so tight that a “year” lasts only 21 hours. This places it in an exclusive group of ultra-short-period hot Neptunes, with only three other planets having their masses precisely measured within this category.
The science team modeled various scenarios to estimate the age and development of the TOI-3261 b system, determining that it is about 6.5 billion years old. Initially, the planet was likely a much larger gas giant. Over time, it lost mass through two main processes: photoevaporation, where stellar energy causes gas to dissipate, and tidal stripping, where the star’s gravity pulls away the planet’s outer layers. The planet may have also formed farther from its star, where these effects would have been weaker, allowing it to retain more of its atmosphere.
The remaining atmosphere of TOI-3261 b is a key feature that could provide insights into its formation history, particularly within the “hot Neptune desert.” The planet’s density is about twice that of Neptune, suggesting that much of its lighter atmospheric components have been stripped away, leaving behind heavier elements.
While it’s unclear which elements remain, studying the planet’s atmosphere in infrared light—potentially using NASA’s James Webb Space Telescope—could reveal its composition’s molecular “fingerprints.” This analysis could shed light on TOI-3261 b’s past and help astronomers understand the physical processes affecting all hot, giant planets.
Journal Reference:
- Emma Nabbie, Chelsea X. Huang et al. Surviving in the Hot-Neptune Desert: The Discovery of the Ultrahot Neptune TOI-3261b. The Astronomical Journal. DOI: 10.3847/1538-3881/ad60be