THE MOST DENSE NEPTUNIAN PLANET EVER OBSERVED

The result of a research published in Nature, with the contribution of two researchers from the University of Florence: Luca Naponiello and Emanuele Pace.

A group of Italian researchers has discovered an exoplanet with a size similar to that of Neptune but with a mass 4 times greater, at a distance of 545 light-years from the Solar System. Exoplanets the size of Neptune are not rare, but they almost never appear so close to their star, within the so-called "Neptunian desert." The new planet, TOI-1853b, is so close to its star that it takes only 30 hours to complete a full orbit. However, its most important characteristic is its density, almost double that of Earth's. According to the lead author of the article, Luca Naponiello: "Neptunian-type planets can have very different densities, but no one expected them to be so compact. This discovery implies that planets of this size can have a much larger amount of heavy materials than previously thought."

The formation of TOI-1853b is also a mystery, and one possibility proposed by the authors is that the planet has a catastrophic origin. "One possibility is that the planet is the result of several proto-planetary collisions that would have removed its atmosphere almost completely, leaving the dense rocky core exposed. If that's the case, TOI-1853b should have a planetary companion not very far away." Alternatively, however, it's also possible that the exoplanet was initially a more massive gas giant than Jupiter, which would have lost its outer layers due to close encounters with the star on an elliptical orbit, which over time would have circularized.

TOI-1853b, as we observe it today, could be almost entirely rocky or composed of rock and water in equal parts. "Understanding the nature of TOI-1853b will be challenging, but we will still try to unveil its atmosphere and therefore its composition, with new observations in the future," Naponiello concludes.

Link to the article: https://www.nature.com/articles/s41586-023-06499-2