Astronomers from the University of California, Irvine have made a profound statement: exoplanets with regions that are perpetually bathed in either light or darkness – known as ‘terminator zones’ – could potentially harbor life.

Exoplanets are planets that reside outside our own solar system. Among these, there is a category of planets that intriguingly exhibit one side perpetually turned towards their star, while the other side remains eternally shrouded in darkness. This creates a unique, ring-shaped boundary known as a “terminator zone”.

A research team, led by Ana Lobo, a postdoctoral researcher at UCI Department of Physics & Astronomy, proposes that life could exist within this borderline. Their work, recently published in The Astrophysical Journal, focusses on planets revolving around M-dwarf stars, which constitute about 70% of the stars we can observe in our night sky.

The unique factor about terminator zones is their positioning – residing between extreme temperatures, they exist in a ‘Goldilocks’ zone. Here, the temperature could be just right for the existence of liquid water, a known prerequisite for life as we understand it.

The scorching temperatures on the star-facing side of the planet may cause water to evaporate rapidly, while the perpetually dark side could be icy cold, with water freezing over. “You could have large glaciers on the night side,” explained Lobo.

The research team, which included Aomawa Shields, UCI associate professor of Physics & Astronomy, manipulated software usually employed for modeling Earth’s climate to model the climates of these terminator planets.

This innovative approach yielded a significant revelation: these planets could indeed sustain habitable climates, confined to the terminator zones. This breakthrough is key, given that researchers have traditionally focused their attention on ocean-covered exoplanets in their search for life-sustaining conditions.


However, Lobo and her team are now shining a light on more “water-limited planets,” which despite lacking widespread oceans, could potentially house smaller bodies of water like lakes. These climates, as per Lobo, could prove promising for life.

The team’s findings suggest that land-rich terminator zone planets have a better shot at retaining liquid water. “Ana has done the work to show that such states can be climatically stable,” Shields stated, further cementing the notion of these ‘exotic habitability states’ no longer being the stuff of science fiction.

This research has immense implications for the study of exoplanet climates, pushing astronomers to revisit how they look for signs of life, or ‘biosignatures’. Signs of life might only be present in specific sections of a planet’s atmosphere.

Furthermore, the findings of Lobo and her team will guide future projects leveraging advanced technology like the James Webb Space Telescope or the Large Ultraviolet Optical Infrared Surveyor telescope currently under development at NASA.

As we extend our search for extraterrestrial life, recognizing the potential of terminator zones to harbor life can significantly increase our chances of discovering habitable planets. As Lobo succinctly puts it, “By exploring these exotic climate states, we increase our chances of finding and properly identifying a habitable planet in the near future.

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