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

Abstract 55 Cancri e (55 Cnc e) is an ∼8 Gyr rocky world (1.95 R ⊕ and 8.8 M ⊕ ) orbiting a K-type star. JWST observations suggest a carbon-dominated atmosphere (CO 2 and CO) over a global magma ocean (>3000 K). We suggest that any CO 2 -dominated atmosphere, with trace amounts of H 2 O and O 2 , 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 postformation cooling. Without tidal heating, an initial 5 wt% water mass fraction ( F H 2 O ) or 3 wt% CO 2 mass fraction ( F CO 2 ) 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 trade-off 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 ultrashort period magma ocean planets, linking age-dependent tidal heating and volatile inventory to the formation and size of secondary atmospheres.