Astronomers have discovered a new Neptune, marking only the fourth planet of its rare type among those known to date.

Astronomers have discovered a new exoplanet, which is a planet outside our Solar System, comparable in size to Neptune. It orbits at a very close distance to its star, categorizing it as a very rare class of planets known as "hot Neptunes." This newly found planet is only the fourth known representative of this class, according to Space.

NASA scientists identified the new "hot Neptune," named TOI-3261 b, using the TESS space telescope. It has been orbiting since 2018 and has already discovered several thousand new exoplanets. The telescope's instruments enable the detection of new planets around dwarf stars, which are smaller and less luminous than the Sun, using the transit method. This means that the telescope detects the planet when it blocks a portion of the light from its star. Astronomers confirmed this new discovery with ground-based telescopes.

The planet TOI-3261 b belongs to the very rare class of worlds known as "hot Neptunes." It is currently the fourth known planet of this class. The first "hot Neptune," the planet LTT-9779 b, was discovered in 2020. Following that, astronomers found two more similar planets — TOI-849 b and TOI-332 b.

As the name suggests, these planets are approximately the same size as Neptune, which is the eighth planet in the Solar System. However, the distinction lies in the fact that "hot Neptunes" orbit their stars at a very close distance. In the case of the new planet TOI-3261 b, a year on it lasts less than an Earth day. This means that this world completes a full orbit around its star in just 21 Earth hours.

In our Milky Way galaxy, astronomers have discovered a significant number of super-Earths or "hot Jupiters." But why have so few "hot Neptunes" been found? There are many hypotheses explaining this. However, the authors of the new study believe that one reason these planets are so rare is that, due to their proximity to their stars, it is more likely that the planet's atmosphere will be destroyed by the star's gravity and radiation. Scientists have found that the density of TOI-3261 b is about twice that of Neptune, indicating that the lighter components of the planet's atmosphere have already been lost.

So far, astronomers do not know the precise process of "hot Neptune" formation, but the authors of the study proposed two possible scenarios based on computer modeling. One suggests that such planets initially had the size of Jupiter but gradually lost mass over time. On the other hand, these planets may have formed further from their stars and then moved to a new, closer orbit where conditions do not allow for the retention of an atmosphere.

NASA scientists plan to use the James Webb Space Telescope for a more detailed study of all four very rare planets. It is hoped that new data will help to understand how they form and uncover other mysteries of these gas giants.