This planet celebrates new year every 21 hours

The planet's very existence challenges current theories, as it's difficult for planets to retain thick gaseous atmospheres so close to their stars1.

In Short

• Proximity to its host star makes it an ideal candidate for testing new computer models
• The star and planet system is about 6.5 billion years old
• They believe TOI-3261 b likely started as a much larger gas giant

Astronomers have discovered a rare type of planet outside Solar System where a year lasts just 21 hours. This newly discovered planet could revolutionise our understanding of planetary formation.

TOI-3261 b, an ultra-hot Neptune-sized planet, has become the latest addition to an elite group of celestial bodies that defy conventional theories of planetary evolution.

The international team of scientists, led by astronomer Emma Nabbie from the University of Southern Queensland, published their findings in The Astronomical Journal in August 2024.

Their paper, "Surviving in the Hot Neptune Desert: The Discovery of the Ultrahot Neptune TOI-3261 b," details this extraordinary planetary system.

TOI-3261 b orbits its star in an extremely close orbit, completing a year in just 21 hours. This proximity to its host star makes it an ideal candidate for testing new computer models of planet formation.

The planet's very existence challenges current theories, as it's difficult for planets to retain thick gaseous atmospheres so close to their stars.

The research team estimates that the star and planet system is about 6.5 billion years old.

They believe TOI-3261 b likely started as a much larger gas giant, possibly Jupiter-sized, before losing a significant portion of its mass. This loss occurred through two primary mechanisms: photoevaporation, where stellar energy causes gas particles to dissipate, and tidal stripping, where the star's gravity pulls away layers of the planet's atmosphere.

Intriguingly, TOI-3261 b is about twice as dense as Neptune, suggesting that only its heavier atmospheric components remain. This characteristic provides a unique opportunity for further study, potentially using Nasa's James Webb Space Telescope to analyze the planet's atmosphere in infrared light.

TOI-3261 b joins a small but growing list of ultra-short-period hot Neptunes discovered since 2020. These rare planets, including LTT-9779 b, TOI-849 b, and TOI-332 b, are helping astronomers unravel the mysteries of planetary formation and evolution in extreme environments.

As scientists continue to study these enigmatic worlds, they hope to gain deeper insights into the physical processes that shape hot, giant planets throughout the universe.