Researchers have discovered a Neptune-sized planet TOI-3261 b orbiting its star every 21 hours, placing it in the category of rare “hot Neptunes”. This planet provides important information about the formation and evolution of the atmospheres of planets close to their stars; this suggests that the initial mass was larger and the atmosphere subsequently disappeared.

Discovery of TOI-3261 b: A rare hot Neptune

TOI-3261 b, a planet about the size of Neptune, orbits extremely close to its host star. It is only the fourth known planet of its kind, offering valuable insight into how such rare planets form.

The discovery was made by an international team of scientists using NASA’s Transiting Exoplanet Survey Satellite (TESS). Subsequent observations using ground-based telescopes in Australia, Chile and South Africa confirmed this finding. TOI-3261 b is located in a region of space that astronomers call “Neptune’s hot desert,” where planets of this size and composition are extremely rare.

TOI-3261 b, similar to Neptune in size and structure, stands out with its extremely narrow orbit and completes a “year” in just 21 hours. This fast orbit places exoplanets in a privileged category: ultra-short-period hot Neptunes, whose masses have been precisely measured, and only three have been identified so far.

Challenges of Neptune’s hot atmosphere

The exoplanet TOI-3261 b turned out to be an ideal candidate for testing new computer models of planet formation. One of the reasons why hot Neptunes are so rare is that it is difficult to have a dense gaseous atmosphere this close to the star. Because stars are so massive, they exert a large gravitational force on objects around them, which can loosen the layers of gas surrounding a nearby planet. They also release large amounts of energy, blowing up layers of gas. Both of these factors mean that hot Neptunes such as TOI-3261 b may have initially become much larger Jupiter-sized planets and have since lost much of their mass.

By modeling different starting points and development scenarios, the research team determined that the star-planet system is approximately 6.5 billion years old and that the planet was originally a much larger gas giant. However, it likely lost mass in two ways: photoevaporation, in which energy from the star causes gas particles to scatter, and tidal dissipation, in which the star’s gravitational pull clears the planet of layers of gas. A planet can also form further away from its star, both of these effects being less intense and allowing it to retain its atmosphere.

Mysteries of the atmosphere and future research

The remnants of its atmosphere, one of the planet’s most interesting features, will likely require further analysis of the atmosphere and perhaps help elucidate the history of the formation of this inhabitant of the “hot desert of Neptune.” Planet TOI-3261 b is about twice as dense as Neptune; This suggests that the lighter parts of its atmosphere have been stripped away over time, leaving only the heavier components.

This suggests that the planet must have started out with many different elements in the atmosphere, but it’s hard to tell exactly which ones at this stage. This mystery could be solved by observing the planet in infrared light, perhaps with NASA’s James Webb Space Telescope; This is an ideal way to see the identifying fingerprints of various molecules in a planet’s atmosphere. This will not only help astronomers understand the history of TOI-3261 b, but will also begin to reveal the physical processes behind all the hot giant planets.

Extension of the hot Neptune club with an ultra-short duration

The first discovery of the ultra-short-period hot Neptune LTT-9779 b occurred in 2020. Since then, TESS discoveries TOI-849 b and TOI-332 b have also joined the elite ultrashort-period hot Neptune. Club Neptune (whose masses were accurately measured). Both LTT-9779 b and TOI-849 b are suitable for infrared observations with the James Webb Space Telescope, potentially expanding our understanding of these planets’ atmospheres in the coming years.

An international research team led by astronomer Emma Nabby from the University of Southern Queensland has published the discovery paper titled “Surviving Neptune’s Hot Desert: Discovery of Ultra-Hot Neptune TOI-3261 b.” Astronomy Magazine In August 2024.