When scientists search for life beyond Earth, they usually look for planets with conditions similar to our own—a world with a stable climate, liquid water, and a regular cycle of day and night. But new research suggests that some of the strangest planets in the universe, where one side is always burning hot and the other is trapped in permanent darkness, might not be as lifeless as they first appear.
A recent study has revealed that these unusual worlds could still create regions with moderate temperatures beneath their surfaces, raising the exciting possibility that life may survive even in places once thought impossible.
A Planet with Two Completely Different Worlds
One fascinating example is LHS 3844b, an exoplanet located about 48.5 light-years from Earth. It is slightly larger than our planet and orbits a small red dwarf star called LHS 3844.
Unlike Earth, LHS 3844b is tidally locked. This means it rotates exactly once every time it completes an orbit around its star. As a result, one side of the planet always faces the star, while the other side always faces away.
The difference between the two sides is astonishing.
The day side experiences temperatures between 1,000 and 2,000 Kelvin, making it incredibly hot. Meanwhile, the night side remains in permanent darkness and could become so cold that scientists compare it to conditions approaching absolute zero, where almost all molecular motion stops.
At first glance, such an environment seems completely unsuitable for life.
Looking Beyond Surface Temperatures
Despite these extreme conditions, researchers believe there may be more to the story.
Daisuke Noto, a postdoctoral researcher at the University of Pennsylvania's Penn GEFLOW Lab, wondered whether life might still find a way to survive.
Instead of focusing only on surface temperatures, he and his team investigated what happens deep beneath the planet's surface, inside its rocky mantle.
Their findings, published in Nature Communications, suggest that tidal locking may actually help distribute heat beneath the surface, creating localized regions where temperatures remain far more stable than expected.
This means that even if the surface is incredibly harsh, the planet's interior could provide environments that are much more favorable.
Tidal Locking Is More Common Than You Think
Although Earth experiences regular day and night, many planets and moons in the universe do not.
Objects that orbit very close to their stars often become tidally locked because the star's gravity gradually slows their rotation until it matches their orbital period.
Our own Moon is a perfect example. It always shows the same face to Earth because it is tidally locked.
Scientists believe many rocky planets orbiting red dwarf stars are also tidally locked. Since red dwarfs are the most common type of star in our galaxy, these permanently divided worlds could be among the most common planets in the universe.
Understanding how they behave is therefore an important step in the search for extraterrestrial life.
Building an Alien Planet in the Laboratory
Obviously, scientists cannot bring an actual exoplanet into a laboratory.
Instead, Noto and his team built a clever experimental model.
They used a tabletop-sized rectangular tank filled with glycerol, a thick liquid that behaves similarly to the slow-moving rock inside planetary mantles.
The fluid was mixed with thermochromic liquid crystals, tiny particles that change color depending on temperature. These colorful particles allowed researchers to see how heat moved through the liquid.
Heating and cooling devices were placed around the tank to recreate the temperature differences between the permanently hot day side and the freezing night side of a tidally locked planet.
Although the setup looked simple, it successfully simulated the slow movement of rock inside an alien planet.
A Giant Planetary Conveyor Belt
The experiment revealed a surprising pattern.
Instead of producing chaotic movement, the mantle settled into one large, stable circulation loop.
Hot material rose beneath the day side, flowed across the upper mantle, cooled as it reached the night side, then sank before returning through the deeper interior.
The cycle repeated continuously, almost like a giant conveyor belt carrying heat from one hemisphere to the other.
Researchers described this steady circulation as resembling a planetary heartbeat.
Unlike Earth's mantle, which constantly changes because of moving tectonic plates, this circulation remained remarkably stable.
Strange Volcano-Like Plumes
The researchers also observed occasional mushroom-shaped plumes of hot material rising from deeper inside the simulated planet.
These plumes are similar to the mantle plumes that create volcanic hotspots on Earth, such as those beneath Hawaii and Iceland.
However, there was one major difference.
On Earth, tectonic plates move over these hotspots, causing volcanoes to appear in different locations over time.
On a tidally locked planet, the plumes stayed fixed in exactly the same place because the mantle circulation remained stable.
This steady heat source could potentially support long-lasting geothermal activity.
Could Underground Life Exist?
One of the most exciting discoveries was that the simulated mantle transported heat almost as efficiently as Earth's mantle.
Scientists measure this using something called the Nusselt number, which describes how effectively heat moves through a material.
Similar values suggest that certain regions of tidally locked planets may maintain stable underground temperatures.
These areas could contain geothermal energy, underground water, and chemical reactions that provide the ingredients needed for life.
Instead of living on the scorching surface or frozen night side, microscopic organisms might survive beneath the ground, especially in regions between the two extremes where temperatures are milder.
Although no life has been found, these results expand the range of places scientists should investigate.
A Different Kind of Magnetic Field
The study also hints at another fascinating possibility.
The steady movement of the mantle could influence the planet's liquid core.
On Earth, motion inside the liquid iron core generates our magnetic field, which protects us from harmful radiation coming from the Sun.
If tidally locked planets have different patterns of mantle circulation, they may produce magnetic fields unlike Earth's.
A magnetic field could help protect an atmosphere from being stripped away by stellar radiation, making long-term habitability more likely.
This idea still needs further investigation, but it opens another exciting area of research.
Rethinking Where Life Can Exist
For many years, scientists believed that planets with permanent daylight and permanent darkness were simply too extreme to support life.
This new research challenges that assumption.
Instead of judging a planet only by its surface temperature, researchers are beginning to explore what happens deep inside its rocky interior.
Stable mantle circulation, geothermal energy, underground heat, and possible magnetic fields could all improve the chances of creating environments where life might eventually emerge.
As scientists continue discovering thousands of exoplanets across our galaxy, studies like this remind us that nature often finds surprising ways to make seemingly impossible worlds more hospitable than expected.
The universe may be far more creative than we ever imagined, and some of its most unusual planets could one day become the most promising places in our search for life beyond Earth.
Reference: Noto, D., Miyagoshi, T., Terada, T. et al. Convective dynamics in mantle of tidally-locked exoplanets. Nat Commun 16, 6846 (2025). https://doi.org/10.1038/s41467-025-62026-z
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