'Terminator zones' of tidally locked exoplanets could harbor alien life

A team of astronomers from the University of California, Irvine, discovered that particular areas on distant exoplanets called "terminator zones" could harbor extraterrestrial life.

The terminator zone of an exoplanet — a planet located outside our solar system — refers to a ring that is always partially facing the planet's host star and partly in the dark.

Exoplanet terminator zones could harbor extraterrestrial life

Exoplanets with terminator zones are particularly common because they exist around a type of star called an M-dwarf, which makes up roughly 70 percent of the stars in the known universe.

These planets are tidally locked, meaning one side always faces the host sun. The so-called terminator zone is the ring around the planet where sunlight gives way to perennial night.

"These planets have a permanent day side and a permanent night side," Ana Lobo, a postdoctoral researcher in the UCI Department of Physics & Astronomy, who led the new work, explained in a press statement.

The researchers, who published their findings in a new paper in The Astrophysical Journal, detail how terminator zones could provide the ideal conditions for life to thrive. As these zones are essentially the dividing line between the day and night side of a planet, they could have ideal temperature conditions.

"You want a planet that’s in the sweet spot of just the right temperature for having liquid water," Lobo explained. "This is a planet where the dayside can be scorching hot, well beyond habitability, and the night side is going to be freezing, potentially covered in ice. You could have large glaciers on the night side."

A new avenue in the search for habitable planets

Lobo and colleagues used computer simulations to model the climate of terminator planets. In a first, they found that these planets may be able to sustain habitable climates confined to the terminator zone.

Astronomers have typically looked to ocean-covered exoplanets in their search for habitable alien worlds. As such, the new findings present a new category of potentially habitable planets. The nature of terminator zones does pose some serious problems for the evolution of life — they would likely inhibit any lifeform from venturing out of this narrow ring. Still, they are a compelling candidate because there is a massive abundance of M-dwarf stars hosting terminator planets in the universe.

"By exploring these exotic climate states, we increase our chances of finding and properly identifying a habitable planet in the near future," Lobo said.