[astro-ph.EP] The number of rocky extrasolar planets being discovered continues to increase, but so too does the apparent diversity of such worlds.
As we work to understand the likely bulk properties and thermal, geological, and climatological attributes we might expect of rocky exoplanets, we can look to the Solar System for guidance.
Here, we review the interior, surface, and atmospheric characteristics of modern Earth, and discuss how our homeworld has changed through Solar System history.
We then visit in turn Venus, Mars, Mercury and Earth’s Moon, and Io, noting how these terrestrial planets are alike, how they are different, and how they have evolved through time.
Finally, we consider some examples of the types of rocky worlds known or suspected to exist without direct Solar System counterparts — but we argue that even then, for all the variety we might expect, they are still variations on a common theme.
Perhaps the most important lesson the Solar System can teach us is that terrestrial bodies change through time, sometimes dramatically, and that rocky worlds of similar size and mass can have vastly different planetary outcomes.
A plot of planetary mass versus radius (relative to Earth, often denoted by ⊕) for known, confirmed exoplanets as of 4 December 2024. Scatter points (with error bars shown) denote all planets with measured radius <4 R⊕ and with measured mass <30 M⊕ values (n = 372). Projected histograms along the X- and Y-axes show the entire sample of planets with at least that quantity measured (n = 448 for mass, n = 581 for radius). The dotted red line marks the planetary radius threshold of <1.6 R⊕, the rule-of-thumb criterion used to classify planets as “rocky” in current practice. There are dozens of known worlds that meet this criterion, some of which are Earth mass or less and thus may have Solar System cognates. Earth, Venus, Uranus, and Neptune are also shown (but not to scale). Data are from the NASA Exoplanet Archive (exoplanetarchive.ipac.caltech.edu) – -[astro-ph.EP]
Paul K. Byrne, Claire Marie Guimond, Peter A. Cawood, Michael J. Way, Doris Breuer, Tilman Spohn, João C. Duarte, Diogo L. Lourenço, Francesca Miozzi, Maëlis Arnould, Nicolas Coltice, Stephanie L. Olson
Comments: 49 pages, 12 figures. Chapter 1 in Space Science Reviews, topical collection ‘The Geoscience of Exoplanets: Going Beyond Habitability’
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.16224 [astro-ph.EP] (or arXiv:2609.16224v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.16224
Focus to learn more
Journal reference: Space Sci Rev 222, 72 (2026)
Related DOI:
https://doi.org/10.1007/s11214-026-01325-3
Focus to learn more
Submission history
From: Claire Marie Guimond
[v1] Mon, 14 Sep 2026 18:52:57 UTC (6,005 KB)
https://arxiv.org/abs/2609.16224
Astrobiology,
