As scientists continue to explore the vast universe, the question arises: Do aliens sleep? While many people take sleep for granted, researchers have discovered that numerous planets capable of supporting life may not have a traditional day-night cycle. By studying organisms thriving in Earth’s extreme environments—such as deep underground or at the ocean’s depths—scientists are beginning to understand what life without a circadian rhythm might look like.
The Milky Way galaxy is home to billions of potentially habitable planets. Current estimates suggest the galaxy contains between 100 billion and 400 billion stars, with around 70% being cool, dim red dwarfs, also known as M-dwarfs. A detailed survey conducted in 2013 revealed that approximately 41% of these M-dwarfs host at least one planet in their “Goldilocks” zone—the ideal distance where conditions may support liquid water.
While these planets may possess the potential for liquid water, it remains uncertain whether any of them actually harbor water or, more importantly, life. Nonetheless, this translates to an astonishing 28.7 billion planets situated within the Goldilocks zones of M-dwarfs alone, not accounting for other star types, including our yellow Sun.
These rocky planets, often referred to as M-Earths, differ significantly from Earth. M-dwarfs are much cooler than our Sun, causing planets to orbit closely and experience stronger gravitational pull. Over time, this gravitational force can synchronize the planet’s spin and orbit, resulting in a state known as tidal locking. Consequently, one hemisphere of the planet remains perpetually illuminated while the other remains in darkness, leading to a unique planetary experience devoid of conventional days, nights, and seasons.
For example, Proxima Centauri b, our closest planetary neighbor located just four light-years away in the Alpha Centauri system, is believed to be a tidally locked M-Earth. In stark contrast to Earth’s diverse climate, M-Earths lack the cyclical patterns that dictate life on our planet, where organisms from bacteria to humans have evolved with circadian rhythms aligned with the day-night cycle.
These rhythms influence a wide range of biological processes, including sleep, metabolism, and immune response. Research has shown that individuals vaccinated in the morning tend to produce more antibodies than those vaccinated later in the day, highlighting the importance of timing in biological functions.
However, the absence of a cyclical time may not impede life on M-Earths. Organisms on Earth that flourish in lightless environments—such as cave-dwelling species, deep-sea creatures, and certain gut bacteria—demonstrate the possibility of life adapting without traditional sleep patterns. Notably, gut bacteria sync with melatonin levels in their human hosts, indicating that even in the absence of light, biological rhythms persist.
Recent studies have also suggested that M-Earths might experience cycles that could serve as substitutes for day-night variations. Scientists have employed climate models to simulate potential environments on M-Earths, including our neighboring Proxima Centauri b, to further investigate these intriguing possibilities.
As researchers continue to ponder the implications of life on tidally locked planets, the question remains: could alien organisms thrive without the need for sleep, or will they develop entirely different biological rhythms? Only time, and further research, will tell.
