Alien Life May Exist in the Zone Between Night and Day, Study Says

Life May Exist in Alien 'Terminator Zones'_548901005677 - Getty Images
  • The search for habitable exoplanets often looks for water-rich worlds similar to Earth.

  • A new study from the University of California-Irvine suggests that water-limited plants, such as tidally locked worlds orbiting Red Dwarf stars, could also be viable candidates.

  • This new research suggests that the thin band between perpetual night and day, known as termination zones, could have just the right ingredients for life to flourish.

How does life thrive on other planets? Although thinking through the particulars of distant alien civilizations has long been the purview of science fiction writers, scientists in search of these extraterrestrial lifeforms only have a sample size of one: planet Earth.

But traveling in a solar system's goldilocks zone with a gentle (at least in a cosmic perspective) 1,000-mph spin that thoroughly spit-roasts the planet to life-generating temperatures isn’t necessarily a universal constant. In fact, Earth’s particular orientation in its solar system could be an outlier among the universe.

So scientists at the University of California-Irvine (UCI) are taking a closer look at an alternative option: eyeball exoplanets. Typically these planets, nicknamed as such because their appearance resembles a human eyeball, orbit Red Dwarf stars and are tidally locked, meaning one hemisphere of the planet experiences scorching temperatures and perpetual daylight while the other is freezing cold and shrouded in neverending darkness.

At first glance, these planets seem too hostile for life, if not for a thin band between these two extremes known as the “termination zone.” UCI post-doc student Ana Lobo and her colleagues tweaked models usually used to understand Earth’s climate to instead mimic conditions of an eyeball exoplanet and found that, with certain conditions in place, a termination zone could theoretically support life.

This isn’t the first study to theorize the possibility of life on eyeball planets, but it does successfully establish that such worlds could be climatically stable. The results were published in The Astrophysical Journal.

“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,” Lobo said in a press statement. “You want a planet that’s in the sweet spot of just the right temperature for having liquid water.”

Although water is essential for life to flourish, for tidally locked planets to be habitable, they specifically can’t have too much water, according to Lobo. If Earth, for example, was tidally locked and orbiting a Red Dwarf star, the oceans continually facing the sun would eventually evaporate and create a thick layer of water vapor that’d make life difficult, if not impossible, to take hold.

But if there’s more land than water, then this runaway water vapor effect wouldn’t occur and melting glaciers from the dark side of the planet could provide sufficient water to support life by filling the termination zone with rivers and lakes.

Understanding the possible habitability of these planets is crucial as Red Dwarfs are the most abundant stars in the universe, and many of these types of worlds are believed to be orbiting them.

“We are trying to draw attention to more water-limited planets, which despite not having widespread oceans, could have lakes or other smaller bodies of liquid water, and these climates could actually be very promising,” Lobo says.

Growing evidence of these worlds as habitable could influence the gaze of the James Webb Telescope or even its successor, the large ultraviolet optical infrared surveyor, as humanity continues its long search to find life among the stars—wherever it might be hiding.

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