Astronomers have discovered a new feature in the distribution of planets beyond the solar system, and this finding could help us understand the dynamics that determine the formation of exoplanets close to their stars.
The discovery — made by a team of scientists from the University of Geneva, the National Centers of Competence in Research (NCCR) Planets group, and the Centro de Astrobiología (CAB) — has been termed the “Neptunian ridge.” The Neptunian ridge is a feature in the distribution of Neptune-sized exoplanets that sits between the called the “Neptunian desert,” where there’s an absence of Neptunian planets close to their star, also known as “hot-Neptunes,” and the “Neptunian savanna,” where there’s an abundance of these worlds existing further out from their star.
The Neptunian desert has long been a puzzling feature to astronomers and planetary scientists, pointing to strange quirks in the evolution of planetary systems.
“We found an overdensity of planets in this region, indicating a sharp transition between the barren Neptunian desert and the more populated Neptunian savanna,” Vincent Bourrier, Assistant Professor at the Astronomy Department of the UNIGE Faculty of Science and co-author of the study, said in a statement.
This newly identified ridge marks a critical zone where planets have managed to migrate inward while resisting intense radiation near their stars.
Related: Why are there so few ‘hot Neptune’ exoplanets?
The desert, the ridge and the savanna
To understand where the concept of the Neptunian desert comes from, it is worth considering how scientists sometimes categorize planets beyond the solar system. Since the discovery of the first extrasolar planet in the mid-1990s, scientists have uncovered over 6,000 planets beyond the solar system, with thousands more awaiting confirmation.
Exoplanets can be of a vast array of sizes and masses, and can exist at different distances from their stars. They’re usually compared to worlds within the solar system so scientists can understand some of their characteristics. So, “super-Jupiters” are planets more massive than Jupiter, super-Earths are more massive than Earth, and sub-Neptunes are planets smaller than Neptune.
The prefix “hot” describes a planet close enough to its star to complete an orbit in mere days or even hours.
Referring to a planet as “Neptune” in this respect doesn’t indicate it is an…
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