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arxiv: 2604.11779 · v1 · submitted 2026-04-13 · 🌌 astro-ph.EP

Origin and characterization of super-Earths and sub-Neptunes

L\'ena Parc , Julia Venturini , Fran\c{c}ois Bouchy , Ravit Helled , Caroline Dorn , Adrien Leleu , Yann Alibert , Simon M\"uller
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Haiyang Wang
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Pith reviewed 2026-05-10 16:03 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords super-Earthssub-Neptunesexoplanet demographicsplanet formationinternal structureatmospheric compositionexoplanet characterization
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The pith

Combined photometric and radial velocity data with theoretical models are revealing the origins and diversity of super-Earths and sub-Neptunes.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper overviews progress in detecting and interpreting super-Earths and sub-Neptunes, the most common exoplanets but without solar system counterparts. Photometric missions and ground-based spectroscopy have supported detailed demographic studies of these planets. Theoretical work on internal structures, bulk compositions, formation, and evolution accounts for the variety observed in the data. Atmospheric measurements are beginning to produce a fuller picture that challenges and refines existing planet formation theories.

Core claim

Super-Earths and sub-Neptunes represent the most common class of exoplanets discovered to date with no direct analogues in the Solar System. The combined data from space-based photometric missions together with ground-based radial velocity campaigns have enabled detailed demographic analyses. These observational efforts are complemented by theoretical work exploring internal structures, bulk compositions, formation and evolution, shedding light on the physical processes responsible for the observed diversity. As high-precision observations begin to probe atmospheric composition, a more complete picture of super-Earth and sub-Neptune origins is emerging that challenges and refines current 0.7

What carries the argument

The synthesis of exoplanet demographic analyses from photometry and radial velocity data with models of internal structure, composition, and formation pathways.

Load-bearing premise

The cited observational campaigns and theoretical models together provide a coherent and sufficiently complete picture of super-Earth and sub-Neptune origins without major unresolved tensions in the data.

What would settle it

Atmospheric composition measurements that show clear and persistent mismatches with the bulk compositions and formation pathways predicted by current models.

Figures

Figures reproduced from arXiv: 2604.11779 by Adrien Leleu, Caroline Dorn, Fran\c{c}ois Bouchy, Haiyang Wang, Julia Venturini, L\'ena Parc, Ravit Helled, Simon M\"uller, Yann Alibert.

Figure 12
Figure 12. Figure 12 view at source ↗
Figure 12
Figure 12. Figure 12: compares the M–R relations from various studies with data from the view at source ↗
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Figure 12. Figure 12 view at source ↗
Figure 12
Figure 12. Figure 12 view at source ↗
Figure 12
Figure 12. Figure 12 view at source ↗
Figure 12
Figure 12. Figure 12 view at source ↗
Figure 3
Figure 3. Figure 3: Histogram of core masses (left) and core radii (right) of the full population with P  100 days, just after formation. Red: fice < 5%, green: 5%  fice < 45%, blue: fice ￾ 45%. Black: all together. The vertical lines indicate the position of the peaks as reported by Fulton et al. (2017). Model A: evap. H-He env Model B: evap. H-He-H2O env view at source ↗
Figure 4
Figure 4. Figure 4: ); that is, they migrated from beyond the ice line. Interest￾ingly, even though most first-peak planets were born dry (i.e. within the ice line), a few also started with water that was then lost. This means that bare rocky cores could also originate beyond the ice line and lose all their volatile content (H, He, and water) due to stellar irradiation. The number of first-peak objects with this origin should… view at source ↗
read the original abstract

Super-Earths and sub-Neptunes represent the most common class of exoplanets discovered to date in our galaxy, yet they have no direct analogues in the Solar System. Since 2014, researchers within the NCCR PlanetS have made significant contributions to understanding the origin and nature of these small planets. This chapter provides an overview of the progress made in their detection, characterization, and theoretical interpretation during the 2014-2025 period. The combined data from space-based photometric missions such as Kepler and TESS, together with ground-based radial velocity campaigns using state-of-the-art spectrographs (e.g., HARPS, ESPRESSO, NIRPS), have enabled detailed demographic analyses of these planets. These observational efforts are complemented by theoretical work exploring their internal structures, bulk compositions, formation and evolution, shedding light on the physical processes responsible for the observed diversity. As high-precision observations from facilities like JWST begin to probe the atmospheric composition of individual planets, a more complete picture of super-Earth and sub-Neptune origins is emerging, one that continues to challenge and refine current planet formation theories.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 1 minor

Summary. The manuscript is a review chapter summarizing NCCR PlanetS contributions (2014-2025) to the detection, demographic analysis, internal structure modeling, and formation theory of super-Earths and sub-Neptunes. It describes how Kepler and TESS photometry combined with RV data from HARPS, ESPRESSO, and NIRPS have enabled population studies, how theoretical work on bulk compositions and evolution complements these data, and how JWST atmospheric observations are beginning to refine planet formation models while highlighting ongoing challenges.

Significance. As a synthesis of observational and theoretical progress on the most common exoplanet class, the review consolidates key advances from a major collaboration and explicitly notes unresolved tensions rather than asserting full coherence. This provides useful context for the field, particularly by linking specific facilities and instruments to demographic insights and theory refinement. No new derivations or predictions are presented, but the descriptive integration of existing results is a strength for readers seeking an overview of recent developments.

minor comments (1)
  1. Abstract: the phrasing 'a more complete picture ... is emerging' could be tempered to better reflect the review's own emphasis on remaining challenges in formation theories.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript and for recommending acceptance. The referee's summary correctly identifies the review's focus on NCCR PlanetS contributions to super-Earth and sub-Neptune research, and we appreciate the recognition that the work consolidates observational and theoretical advances while noting unresolved issues.

Circularity Check

0 steps flagged

Review paper with no derivations or predictions; no circularity present

full rationale

This is a descriptive review summarizing external observational campaigns (Kepler, TESS, HARPS, ESPRESSO, NIRPS) and theoretical modeling on super-Earths and sub-Neptunes from NCCR PlanetS contributions 2014-2025. The text contains no original equations, derivations, fitted parameters, or predictions that could reduce to inputs by construction. All statements are attributed to cited literature or noted as ongoing challenges, with no load-bearing self-citations, ansatzes, or uniqueness claims that close a loop. The argument is self-contained as a literature overview without deductive steps.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Review paper containing no new mathematical derivations, fitted parameters, axioms, or postulated entities; all content references prior published work.

pith-pipeline@v0.9.0 · 5525 in / 1026 out tokens · 39908 ms · 2026-05-10T16:03:20.364761+00:00 · methodology

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Works this paper leans on

9 extracted references · 9 canonical work pages

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