When it comes to prime real estate for liquid water in the cosmos, location is everything. Too close to a star, and a planet’s water evaporates from the extreme heat. Too far, and the planet turns into an ice ball. The middle is the place to be. Anything beyond that outermost edge, where planets can’t retain enough warmth, is icy and desolate.
Or maybe not. In a study published Monday in the Astrophysical Journal Letters, a pair of researchers suggest a geological phenomenon could keep some planets beyond that edge warm enough to support liquid water—and maybe even life. They argue that the habitable zone, the lucky strip of space where life could emerge, may be bigger than previously thought.
The geological phenomenon is a well-documented one here on Earth: volcanoes. The researchers suggest that volcanic activity on a given exoplanet, spurred by the shifting of tectonic plates, could churn out enough hydrogen to warm its atmosphere even further out in a star system, with only little help of the parent star’s heat. Hydrogen is a very light gas, so the planet would be constantly losing it to space. But volcanoes could spew out hydrogen at a rate that keeps up with that loss, creating a steady amount of hydrogen in the atmosphere capable of helping to heat the planet. That warmth, in turn, could create conditions favorable for liquid water and other chemical compounds on the planet’s surface that would spark life. Using climate models, the researchers found the distance from a star at which volcanoes create enough heat through this process without freezing over. That spot constitutes a new outer edge of the habitable zone, about 50 percent wider than before.