[astro-ph.EP] Habitability is typically defined by whether a planet can support life, rather than whether it can support a technological civilization capable of escaping its gravity well.
We introduce spacefaring capability as a technological axis of habitability, defined by the ability to place a 1000 kg payload on an escape trajectory using chemical propulsion. We develop a coupled geophysical–atmospheric–astronautical model that maps this “spacefaring envelope” as a function of planetary mass and surface pressure.
Building on Hippke (2018) and Gonzalez (2020), we optimize multistage chemical rockets by minimizing the reliability-weighted expected launch mass while determining the optimal stage count, first-stage engine number, and mission reliability. Assuming F-1-class first-stage engines, the model reproduces the Saturn V gross lift-off mass to within ∼30% and the F-1 turbopump power to within ∼18%. Over 0.1–10~bar, atmospheric pressure changes the required launch mass by up to ∼35% on 0.5M⊕ planets, where drag contributes substantially to the ascent Δv, but by only a few percent for M⊕≳4.
Gravity, rather than atmospheric drag, therefore sets the primary limit on chemical escape from super-Earths. Imposing a post-optimization limit of ∼100 F-1-class first-stage engines renders escape of the benchmark payload impractical above ∼11.5M⊕. This engine-counting constraint independently corroborates the ∼10M⊕ limit derived by Hippke (2018) from an engine-independent fuel-ratio argument.
These results provide a physically motivated framework for assessing whether rocky exoplanets are capable of supporting technological civilizations that can escape their planetary gravity wells.
Geophysical constraints from Sec. 2.2 as a function of planetary mass (log–log axes). (A) Mantle Rayleigh number Ra with onset (Ra = 103 ) and robust-convection (Ra = 106 ) bands. (B) Core magnetic Reynolds number Rm with dynamo-onset (Rm = 50) and robust-dynamo (Rm = 100) bands. Blue curves: this model; markers: Earth, Mars (M/M⊕ ≈ 0.11), and Kepler-20 b (10 M⊕, 1.7 R⊕; Hippke 2018). At Mars the model gives Ra ≈ 1.6 × 106 and Rm ≈ 220, i.e. robust convection and a robust dynamo under the adopted scalings, even though Mars today lacks plate tectonics and an active global magnetic field (an ancient dynamo is recorded in crustal magnetization). Mars therefore illustrates the limit of this mass-only, equilibrium approach: Ra and Rm test convection vigor and dynamo capacity, not tectonic mode or dynamo longevity. Kepler-20 b is a super-Earth (Ra ≈ 3.7 × 109 , Rm ≈ 3.6 × 103 ) and passes both thresholds. — [astro-ph.EP]
Sanjoy M. Som
Comments: 15 pages, 4 figures, 4 tables, IAUS 404: Advancing the Search for Technosignatures technical proceeding
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2607.02691 [astro-ph.EP] (or arXiv:2607.02691v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.02691
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Submission history
From: Sanjoy Som
[v1] Thu, 2 Jul 2026 18:32:52 UTC (985 KB)
https://arxiv.org/abs/2607.02691
Astrobiology,
