Why are Neptune-sized planets missing from the region closest to their stars?

Space · Published 23 October 2026 Swipe more like this →

In short: Astronomers have found plenty of scorching rocky worlds and massive gas giants, but a mysterious gap exists in between. This 'Neptunian Desert' is a cosmic zone where large, gaseous atmospheres should theoretically evaporate, leaving only barren, rocky cores behind.

The Neptunian Desert refers to a specific region near stars where 'hot Neptunes'—planets with hydrogen and helium-dominated atmospheres—appear to be remarkably rare. While we frequently observe 'hot Jupiters' like 51 Pegasi b and 'super-Earths' like 55 Cancri e in close orbits, planets with Neptune-like proportions are missing. The prevailing theory is that intense stellar irradiation causes the gaseous envelopes of these planets to evaporate, stripping them down to their rocky interiors.

However, a recent discovery by an international team of astronomers has challenged this scarcity. Using the Next-Generation Transit Survey (NGTS) at the European Southern Observatory in Chile, researchers identified NGTS-4b, a planet nicknamed the 'Forbidden Planet.' Despite orbiting its star in the heart of the desert, NGTS-4b has managed to keep its atmosphere intact. This world is significantly denser than Neptune, possessing a mass 20 times that of Earth and a radius roughly three times larger.

The existence of NGTS-4b raises fascinating questions about planetary survival. Scientists, including Dr. Ed Gillen of Cambridge and Dr. Richard West of the University of Earth, suggest two possibilities: the planet may have migrated into this harsh orbit only recently—within the last one million years—or it was originally much larger and is currently in the process of losing its atmosphere. This discovery forces astronomers to reconsider whether the Neptunian Desert is as barren as once thought.

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