Tides Tighten the Hycean Habitable Zone

TL;DR

This paper demonstrates that tidal heating significantly influences the habitable zone of hycean planets, especially around low-mass stars, by extending the zone due to tidal effects and affecting potential biosphere development.

Contribution

It introduces the impact of star-planet tidal interactions on the habitable zone boundaries of hycean planets, a factor previously overlooked.

Findings

Tidal heating can truncate the habitable zone at larger orbital distances.

Moderate eccentricity in hycean planets is common and affects habitability.

Tidal effects are crucial for future assessments of hycean planet habitability around M dwarfs.

Abstract

Hycean planets -- exoplanets with substantial water ice layers, deep surface oceans, and hydrogen-rich atmospheres -- are thought to be favorable environments for life. Due to a relative paucity of atmospheric greenhouse gases, hycean planets have been thought to have wider habitable zones than Earth-like planets, extending down to a few times 0.001 au for those orbiting M dwarfs. In this Letter, we reconsider the hycean habitable zone accounting for star-planet tidal interaction. We show that for a moderately eccentric hycean planet, the surface temperature contribution from tidal heating truncates the habitable zone at significantly larger orbital radii, and that moderate eccentricity is readily obtained from any massive outer companion in the system. Though few current hycean planet candidates orbit stars of low enough mass for tides to plausibly significantly alter the extent of the habitable zone, this effect will be important to note as more such candidates are identified orbiting M dwarfs. We suggest that tides are a significant factor both for determining the extent of the hycean habitable zone around low-mass stars and for the development of a detectable hycean biosphere.