In a new study, University of California, Irvine astronomers describe how extraterrestrial life has the potential to exist on distant exoplanets within a special region called the “terminal zone,” a ring on planets that has one side always facing its star and one side always dark. .
“These planets have a permanent day side and a permanent night side,” said Anna Lobo, a postdoctoral researcher in the UCLA Department of Physics and Astronomy who led the new work, which was just published in. Astrophysical Journal. Lupo added that such planets are particularly common because they are found around stars that make up about 70 percent of the stars visible in the night sky — so-called M dwarf stars, which are relatively darker than our sun.
The separator is the line separating the day and night sides of the planet. Terminator regions can exist in the “just right” temperature region between very cold and very cold.
“You want a planet in the sweet spot with the right temperature to have liquid water,” Lupo said, because, as far as scientists know, liquid water is an essential ingredient for life.
On the dark sides of the separator planets, perpetual night will result in lower temperatures that could cause any water to freeze into ice. The side of the planet facing its star may always be too hot for water to remain in the open for long.
“This is a planet where the day side could be very hot, beyond its habitability, and the night side would be frigid, potentially covered in ice. You could have large glaciers on the night side,” Lobo said.
Lobo, along with Aomawa Shields, Associate Professor of Physics and Astronomy at UCI, modeled the interplanetary climate using software typically used to model our own planet’s climate, but with some modifications, including slower planetary rotation.
It is believed to be the first time astronomers have been able to show that such planets can maintain habitable climates confined to this final region. Historically, researchers mostly studied exoplanets covered in oceans in their search for habitable candidates. But now that Lobo and her team have shown that exoplanets are also habitable refuges for life, it increases the options that life-seeking astronomers have to choose from.
“We’re trying to bring attention to more water-limited planets, which although they don’t have pervasive oceans, could have lakes or other bodies of liquid water, and those climates could actually be very promising,” Lobo said.
One of the keys to this discovery, Lobo added, is pinpointing the exact type of buffer zone planet that could hold liquid water. The team found that if the planet was mostly covered in water, the water facing the star would likely evaporate and cover the entire planet in a thick layer of vapor.
But if there is land, this effect should not occur.
“Anna showed that if there was a lot of land on the planet, a scenario we call ‘terminator habitability’ could exist much more easily,” Shields said. “These strange new habitat states our team is discovering are no longer the stuff of science fiction – Anna has done the work to show that such states can be climatically stable.”
Recognizing end zones as potential harbors for life also means that astronomers will need to adjust the way they study exoplanet climates for signs of life, because the vital signatures that life creates may only be present in certain parts of a planet’s atmosphere.
The work will also help inform future efforts of teams using telescopes such as the James Webb Space Telescope or the Large Ultraviolet Infrared Scanner Telescope currently under development at NASA as they search for planets that might host extraterrestrial life.
“By exploring these exotic climatic conditions, we increase our chances of finding and properly identifying a habitable planet in the near future,” Lupo said.
