Alien planets might experience tidal forces powerful enough to remove all their water, leaving behind hot, dry worlds like Venus, researchers said. These findings might significantly affect searches for habitable exoplanets, scientists explained. Although some planets might dwell in regions around their star friendly enough for life as we know it, they could actually be lifelessly dry worlds.
The tides that we experience on Earth are caused by the gravitational pull of the moon and sun. Our tides are nothing compared to what we see elsewhere in the solar system — the gravitational pull Europa experiences from Jupiter leads to tidal forces roughly 1,000 times stronger than what Earth feels from our moon, flexing and heating Europa. Heat is a major factor in how capable a planet might be of supporting life as we know it. What scientists call the habitable zone of a star is defined by whether liquid water can survive on its surface, given that life exists virtually wherever there is liquid water on Earth.
Too far from a star, and the lack of light makes a world too cold, freezing all its water; too close to a star, and all that blazing heat makes a world too hot, boiling all of its water off in what is known as a runaway greenhouse effect. Venus is often thought to have experienced a runaway greenhouse effect. Eventually, solar radiation broke up all of Venus’s vaporized water into hydrogen and oxygen, which leaked away from the planet entirely.
Now scientists find that stellar heat is not the only thing that can trigger a runaway greenhouse climate catastrophe. Tidal heating can too, for what they call ‘tidal Venuses.’ “This has fundamentally changed the concept of a habitable zone,” said researcher Rory Barnes, a planetary scientist and astrobiologist at the University of Washington. “We figured out you can actually limit a planet’s habitability with an energy source other than starlight.”