Exoplanets Termed ‘Tidal Venuses’ Might Have Experienced Significant Desiccation

Earth-sized exoplanets located within the habitable zone of a distant star may not necessarily be suitable for life due to potential tidal stresses. These stresses, whether they occurred in the past or are currently happening, could have caused the complete evaporation of water, leaving behind a dry and barren planet.Recent research conducted by an international team of scientists suggests that even a moderately eccentric orbit within a star’s habitable zone could result in tidal stress on an Earth-sized planet. This stress would generate increased surface heating through friction, leading to the boiling off of any liquid water due to an extreme greenhouse effect.These particular exoplanets are referred to as “Tidal Venuses” due to their resemblance to our own scorching-hot neighboring planet. This evolutionary possibility plays a significant role in determining the habitability of an exoplanet, regardless of the amount of solar heating it receives from its star.

The study, led by Dr. Rory Barnes from the University of Washington in Seattle, explains that even an exoplanet currently in a stable, circular orbit could have initially formed with a highly eccentric orbit, subjecting it to tidal forces. Any liquid water that existed during its formation would have gradually evaporated over time, with the hydrogen atoms necessary for sustaining life being lost to space.The risk of this “desiccating greenhouse” effect is particularly high for exoplanets orbiting stars with lower luminosity. In such cases, the potential habitable zone would be closer to the star, resulting in stronger tidal forces and a greater likelihood of water loss.

Moreover, if such an effect were to occur and create habitable zones beyond what stellar radiation alone allows, it does not necessarily guarantee favorable conditions. Even if a moon-like exoplanet such as Europa could maintain liquid water on or beneath its surface due to tidal forces, a rocky planet the size of Earth or larger would likely still be inhospitable. Dr. Barnes explained that the interior’s tidal heating would result in a surface dominated by super-volcanoes, making it unsuitable for an Earth-like planet. Therefore, even if exoplanets of the right size are located within the “Goldilocks zone” of their star, they may not be suitable for life as we currently understand it.

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