According to a new proposal, a phenomenon known as super-rotation may mean that tidally locked exoplanets, or planets whose orbits are locked to their host star, are also now potential candidates in the hunt for extraterrestrial life. Astrobiologists and other non-Earth based life hunters have previously discounted these bodies, but this latest proposal offers a roadmap that seems to put these types of common planets back on the list when searching for extraterrestrial life.
BACKGROUND: TIDALly LOCKed AND WATER problems
On Earth, water and life go hand in hand. And although no signal of life outside of Earth has yet to be definitively detected, astrobiologists have prioritized planets in their host star’s habitable zone as targets for the hunt for E.T. That’s because planets at this preferred stellar orbit are in the exact right place to allow for liquid water to exist on their surface, something we experience as key for life.
Now, this latest proposal from Northrop Grumman’s NOW website suggests that even tidally locked planets that orbit extremely close to their host stars may have a mechanism, known simply as super-rotation, that would allow them to retain liquid water even though one side of the planet is in permanent darkness, and the other side is in permanent sunlight.
ANALYSIS: RED DWARF STARS AND SUPER-ROTATION
“If all stars were as bright as the sun, these close-orbiting (tidally locked) planets would still be ruled out,” the post explains, “the entire planet, even the perpetual night side, would grow baking hot.”
However, the post notes, most stars we see in the sky are not like our Earth, but instead are a much smaller, much dimmer ball of nuclear fusion known as a Red Dwarf. For example, The Debrief previously covered the efforts of astronomers who plan to use the soon-to-be-launched James Webb Telescope to search the red dwarf star Trappist-1 for signs of life on one of the seven exoplanets already identified within its system.
Now, the post notes, “recent research and modeling, reported in the Astrophysical Journal, suggests that natural processes on some tidally locked planets could allow surface water to remain liquid without either boiling away or freezing.”
That process is super-rotation, or as the post explains it, “a steady wind or current strong enough to go around the planet faster than the solid planet’s rotation speed.”
Such a current could, in theory, allow the water on the sun side to stay cool enough without evaporating, while also sending enough energy to the cold side to keep all of the water stuck in perpetual darkness from freezing.
“This sounds vaguely like magic,” the post admits, “but it isn’t: It just takes energy, ultimately derived from starlight.”
The result of this super-rotation, the post clarifies, is how that energy is redistributed across the planet.
“Atmospheres and oceans don’t simply stay in one place, waiting to be boiled or frozen. They develop winds and currents. And if these are strong enough, in the right place, and blowing or flowing in the right direction, they can transfer heat from the dayside to the nightside efficiently enough to preserve liquid water.”
OUTLOOK: ANOTHER PLACE TO SEARCH FOR LIFE
Most current life hunting missions are focused on rocky planets within a star’s habitable zone. And to date, none of those candidates slated for study is tidally locked. However, if this new theory proves to be fact, and these types of common planets around particularly common stars are viable candidates, the situation may change.
“If super-rotation proves to be common in the universe, the search for habitable exoplanets will be revolutionized,” the post concludes. “Our exoplanet search technology is already able to detect winds on exoplanets, and our capabilities continue to grow. If planets orbiting in the habitable zones of red dwarf stars can be candidates for habitability, examining them could be a very busy research program in decades to come.”
Follow and connect with author Christopher Plain on Twitter: @plain_fiction