Exoplanets, -moons, -comets

The Effect of Tidal Heating and Volatile Budgets on the Outgassed Atmosphere of 55 Cancri e

By Keith Cowing
Status Report
astro-ph.EP
February 5, 2026
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The Effect of Tidal Heating and Volatile Budgets on the Outgassed Atmosphere of 55 Cancri e
Grid of simulations of atmospheric pressure contribution (bars) and total volume mixing ratio (VMR) for each molecular species as a result of initial volatile abundances. Results are shown for the current age of the system and assume no tidal heating (e = 0). Small black dots denote the simulation grid points. Top Left: CO2 atmospheric pressure (bars). Top Center: H2O atmospheric pressure (bars). Top Right: O2 atmospheric pressure (bars). Bottom Left: CO2 VMR. Bottom Center: H2O VMR. Bottom Right: O2 VMR. — astro-ph.EP

55 Cancri e is a ∼8 Gyr rocky world (1.95 R⊕, 8.8 M⊕) orbiting a K-type star. JWST observations suggest a carbon-dominated atmosphere (CO2/CO) over a global magma ocean (>3000 K).

We suggest that any CO2-dominated atmosphere, with trace H2O/O2, likely arises from outgassing of its initial volatile reservoir.

As solidification drives the magma ocean and atmosphere away from solution-equilibrium, tidal and greenhouse heating can prolong outgassing. Early atmosphere outgassing reflects rapid degassing of the volatile-saturated melt during post-formation cooling. Without tidal heating, an initial 5 wt% water mass fraction (FH2O) or 3 wt% CO2 mass fraction (FCO2) can sustain outgassing for at least ∼10 Myr.

With both at 10 wt%, greenhouse warming alone can prolong outgassing up to ∼30 Myr. Our model shows that tidal heating can reduce the volatile threshold required to maintain a high surface temperature (∼3200 K at e=0.005) and delay outgassing of additional volatiles to the present-day. However, higher tidal heating presents a tradeoff between prolonging tenuous outgassing and enlarging the overall size of the secondary atmosphere. Tidally-enhanced outgassing may produce minor pressure variations that could contribute to the observed phase-curve variability.

Additionally, our model shows that tidal heating strongly controls outgassing in the planet’s young-to-midlife stage, then shifts toward a volatile inventory dependence at mature ages. Using 55 Cnc e, we present a framework to prioritize atmosphere detections on rocky ultra short period (USP) magma ocean planets, linking age-dependent tidal heating and volatile inventory to the formation and size of secondary atmospheres.

Barron K. Nguyen, Laura K. Schaefer, Fei Dai, Héctor E. Delgado-Díaz

Comments: Accepted for publication in ApJ (The Astrophysical Journal), 2026
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2601.23235 [astro-ph.EP] (or arXiv:2601.23235v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2601.23235
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Related DOI:
https://doi.org/10.3847/1538-4357/ae3f21
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Submission history
From: Barron Nguyen
[v1] Fri, 30 Jan 2026 18:06:02 UTC (2,749 KB)
https://arxiv.org/abs/2601.23235

Astrobiology, Astrochemistry,

Keith Cowing

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) 🖖🏻

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