Origin & Evolution of Life

Solar Hegemony: M-Dwarfs Are Unlikely to Host Observers Such as Ourselves

By Keith Cowing
Status Report
astro-ph.IM
October 7, 2025
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Solar Hegemony: M-Dwarfs Are Unlikely to Host Observers Such as Ourselves
Number of stars capable of hosting observers (amongst a sample of 106) as a function of time. The darkest track assumes that all stars are equally capable of hosting life during their MS lifetime. Each lighter track sequentially truncates the lowest mass star capable of hosting observers in 0.02 MβŠ™ steps. One can see that removing low-mass stars gradually relaxes the tension as to why we live so early in the stelliferous period. — astro-ph.IM

With no firm evidence for life beyond our solar system, inferences about the population observers such as ourselves rests upon the Earth as a single input, at least for now.

Whilst the narrative of our home as a ‘humdrum’ system has become ingrained in the public psyche via Sagan, there are at least two striking facts about our existence which we know are certainly unusual.

First, the stelliferous period spans ~10Tyr – yet here we are living in the first 0.1% of that volume. Second, over three-quarters of all stars are low-mass M-dwarfs, stars with no shortage of rocky habitable-zone planets – and yet, again, our existence defies this trend, previously dubbed the Red Sky Paradox.

Two plausible resolutions are that a) stars below a certain mass, Mcrit, do not produce observers, and, b) planets have a truncated temporal window for observers, Twin, negating the longevity advantage of M-dwarfs. We develop a Bayesian model that encompasses both datums and jointly explores the two resolutions covariantly.

Our analysis reveals that 1) the hypothesis that these observations are mere luck is disfavored with an overwhelming Bayes factor of ~1600; 2) some truncation of low-mass stars is indispensable, lowering Twin alone cannot well-explain the observations; and, 3) the most conservative limit on Mcrit occurs when fixing Twin=10Gyr, yielding Mcrit>0.34MβŠ™ [0.74MβŠ™] to 2Οƒ [1Οƒ]. Our work challenges the tacit assumption of M-dwarfs being viable seats for observers and, indirectly, even life.

David Kipping

Comments: Submitted to AAS Journals
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2510.01215 [astro-ph.IM] (or arXiv:2510.01215v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2510.01215
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Submission history
From: David Kipping
[v1] Fri, 19 Sep 2025 08:15:13 UTC (3,183 KB)
https://arxiv.org/abs/2510.01215
Astrobiology, SETI,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»