Sub-Neptunes Dominate Milky Way Surveys Despite 1.5-2 Earth-Radius Mystery
Updated
Updated · spacedaily.com · Jul 13
Sub-Neptunes Dominate Milky Way Surveys Despite 1.5-2 Earth-Radius Mystery
2 articles · Updated · spacedaily.com · Jul 13
Summary
Exoplanet surveys keep turning up sub-Neptunes—planets larger than Earth but smaller than Neptune—even though the Solar System has no example of this now-common class.
Kepler data sharpened the puzzle with a size gap at roughly 1.5 to 2 Earth radii, suggesting similar young planets can split into bare rocky worlds or gas-retaining sub-Neptunes.
48-light-year-away GJ 1214 b shows why they remain hard to decode: JWST and earlier spectra were largely obscured by clouds or haze, limiting clear readings of atmospheric chemistry.
Researchers say mass and radius alone cannot distinguish rocky cores with thin hydrogen envelopes from water-rich or mini-Neptune-like interiors, leaving the class physically unresolved.
The broader implication is that planet formation may routinely produce worlds missing from our own system, making the Solar System unusual rather than a standard template.
Why is our Solar System a cosmic outlier, lacking the galaxy's most common planet?
Are the galaxy's most common planets hiding their atmospheres behind vast clouds of soot?
Could planets brew their own oceans without needing water delivery from asteroids or comets?
Exoplanet Size Gaps and Sub-Neptune Diversity: New Insights into the Radius Valley and Planetary Evolution (2026)
Overview
Sub-Neptunes, planets larger than Earth but smaller than Neptune, are common throughout the galaxy but are missing from our own solar system, creating a major mystery for astronomers. Thanks to missions like TESS, scientists can now compare thousands of planetary systems and have discovered a striking feature called the radius valley—a gap in planet sizes around 1.7 Earth radii. This valley separates rocky super-Earths from larger sub-Neptunes and is thought to result from atmospheric loss processes. These findings challenge old ideas and help researchers develop a clearer understanding of how different types of planets form and evolve.