Recently, new progress has been made in research on the habitability of star planets (also known as ocean worlds). Star planets are planets covered by oceans, with thick hydrogen atmospheres. Although no confirmed examples exist yet, researchers are full of curiosity about their potential habitability.
In a study soon to be accepted for publication in The Astrophysical Journal, authors including Joseph Lifson from the Department of Astronomy at the University of Wisconsin-Madison and the Wisconsin Center for Origins and Astrobiology explored the role of tidal heating in the potential habitability of star planets. They believe that for star planets close to low-mass stars, tidal heating may be an important factor determining their habitable zone.
Star planets are vastly different from terrestrial planets; they have vast layers of water and atmospheres dominated by hydrogen. The study points out that since star planets are expected to orbit closely around their stars, tidal heating could alter their habitable zones. Compared to land habitable zones, the semi-major axis of star planet habitable zones may be smaller and could even extend to unbound planetary orbits.
The researchers further explain that tidal heating, in addition to stellar radiation, produces another heat source. Star planets orbiting along moderate eccentricity orbits will experience tidal flexing and heating, causing the habitable zone to shift outward. This effect depends on a more massive companion star that can introduce eccentricity to the star planet's orbit.
Although star planets are still hypothetical at present, their confirmation may not be far off. Exoplanet scientists are very interested in them because of their habitability potential. Additionally, the vast atmospheres of star planets also make them ideal targets for telescopes to conduct atmospheric spectroscopic analysis. For example, the candidate star planet K2-18b has frequently made headlines because astronomers detected water vapor, carbon dioxide, and methane in its atmosphere, as well as the potential biosignature dimethyl sulfide.
The researchers point out that on star planets with deep oceans, ocean tides would generate a large amount of heat available for biological use. They believe that strong tides on star planets may provide important energy sources for life and ultimately accelerate biological evolution.
