Deep in space, 48.5 light-years from Earth, a rocky world called LHS 3844b circles a small, cool star called a red dwarf. One side of this planet bakes in permanent, scorching sunlight, while the other side freezes in endless darkness. It sounds like the nightmare planet from a science fiction movie. But scientists now think such worlds might not be so hostile after all.
LHS 3844b is slightly bigger than Earth—about 1.3 times our planet's mass. It was discovered back in 2018 by NASA's Transiting Exoplanet Survey Satellite (TESS), a space telescope that watches for planets passing in front of distant stars. Because LHS 3844b hugs its star so closely, completing one full orbit in just 11 hours, it is what scientists call tidally locked. Just like our own moon always shows the same face to Earth, one side of LHS 3844b forever faces its star while the other faces outward into the cold void.
On the sunny side, temperatures can reach a blistering 1,000 to 2,000 Kelvin (roughly 1,340 to 3,140 degrees Fahrenheit). On the dark side, temperatures drop to absolute zero—minus 459 degrees Fahrenheit—cold enough that particles simply stop moving. Given those extremes, you might assume no life could survive there.
But Daisuke Noto, a postdoctoral researcher at the University of Pennsylvania, isn't so sure. "Just looking at the extreme temperatures on the day and night sides might lead one to conclude these exoplanets are too harsh for life," Noto says. "But life might find a way."
In a study published in the journal Nature Communications, Noto and collaborators at the Japan Agency for Marine-Earth Science and Technology and Hokkaido University discovered something surprising. Using a simple tabletop tank filled with a thick fluid called glycerol and tiny colorful particles that change color with temperature, they mimicked the conditions inside a tidally locked planet's mantle—the rocky layer between a planet's crust and its core.
The experiment showed heat flowing from the hot day side to the cold night side in a steady, predictable loop. Hot material rises on the sunny side, travels across the surface, cools down, sinks, and flows back along the bottom. "It's slow and steady," Noto explains. "Predictable. Kind of boring—but in a good way."
That boring stability might be exactly what life needs. The researchers found that this gentle heat circulation could create a temperate "twilight zone" between the scorching day side and the frozen night side—temperatures mild enough that liquid water and possibly life could exist.
Notably, planets like LHS 3844b are not rare. Most planets orbiting close to red dwarf stars are probably tidally locked, making them the most common type of planet in our galaxy. If even some of these worlds have habitable zones, the odds of finding life elsewhere in the universe suddenly look a lot better.
For Noto, the takeaway is simple: don't count out a planet just because it looks extreme from the outside. Life has a history of surprising us. "Just looking at the extreme temperatures might lead one to conclude these exoplanets are too harsh for life," he says. "But life might find a way."