[astro-ph.IM] Sub-Neptunes are the most common class of planets in the Galaxy, yet they have no Solar System analog and remain poorly understood as a population. JWST observations have revealed atmospheres spanning a wide range of metallicities, compositions, and cloud properties, driving active debates over whether warm sub-Neptunes harbor liquid water oceans beneath H2-rich envelopes, maintain stratified H2/H2O interiors, or have well-mixed, metal-rich envelopes.
Open questions also remain over what physical processes drive transitions between hazy and clear atmospheres. These are intrinsically population-level questions that single-target observations, however deep, cannot resolve.
Here we argue that a sub-Neptune population survey with the Nautilus Space Observatory, a proposed constellation of large-diameter space telescopes, would deliver the first statistical map of sub-Neptune atmospheric diversity, test competing classification schemes, identify habitable candidates, and serve as a pathfinder population for the eventual habitable-worlds search.
These goals are achievable across the proposed mission classes for the constellation, and this architecture is uniquely well-matched to this science case since population-level questions demand sample size and a uniform observing strategy.
Luis Welbanks, Kylie E. Hall, Julien de Wit, Ana Glidden, Noah Tuchow, Ilaria Pascucci, Dániel Apai, Robin Wordsworth, Benjamin V. Rackham, Chia-Lung Lin, Raymond Pierrehumbert, Mercedes López-Morales, A. D. Feinstein
Comments: White Paper for the Nautilus Space Observatory
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2607.00268 [astro-ph.IM] (or arXiv:2607.00268v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2607.00268
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Submission history
From: Luis Welbanks
[v1] Tue, 30 Jun 2026 23:32:53 UTC (408 KB)
https://arxiv.org/abs/2607.00268
Astrobiology, exoplanet,
