Exoplanet in the hot-Neptune desert is the first of its kind - Ars Technica

In 2018, scientists monitoring TESS—the Transiting Exoplanet Survey Satellite—discovered a giant planet in close orbit around the star TOI-849, roughly 735 light years away.

TOI-849b is roughly 40 times the mass of Earth, which would normally indicate a gas giant, weighing in somewhere between Saturn and Neptune. Yet its radius is smaller than Neptune's, although it has more than double Neptune's mass.

TOI-849b's host star is a late G-class yellow dwarf, a little cooler and approximately 2 billion years older than our Sun, with about nine-tenths its mass and radius.

TOI-849b is very close to its host—its orbital period is a little over 18 hours.

The radius, mass, and period of TOI-849b place it firmly in a zone that's called the "hot-Neptune desert"—an orbital region where the physics are such that large planets appear to very rarely form.

The rarity of planets with large mass and close orbital period is likely due to a combination of two processes driven by the star: photoevaporation and tidal disruption.

Although we don't yet know the details of TOI-849b's unusual formation and history, its discovery offers astrophysicists fascinating clues about the mechanics of planetary formation and new insights into the likely composition of gas giant cores.