LHS 3844b is a fascinating exoplanet, slightly larger than Earth, orbiting the red dwarf star LHS 3884, located 48.5 light-years away from our solar system. Unlike Earth, this unique planet experiences fixed tidal forces and rotates on its axis in perfect synchronization with its orbital period. Consequently, one hemisphere faces perpetual scorching sunlight, while the other remains in eternal darkness, with temperatures plummeting close to absolute zero (zero Kelvin).
At first glance, these extreme environments appear completely inhospitable. Daytime temperatures soar to approximately 1,000 to 2,000 Kelvin, while the night side becomes so frigid that molecular movement virtually halts. However, recent studies indicate that these worlds might be more amenable to hosting life than previously thought.
“At first, one might assume that the extreme temperature differences between the dayside (1,000 to 2,000 Kelvin) and nightside (near absolute zero) make these exoplanets too hostile for life,” states Daisuke Noto, a postdoctoral fellow at the University of Pennsylvania’s Hugo Ulloa’s Penn-Geffrow Laboratory.
In research published in Nature Communications, Noto and his collaborators from the Japan Agency for Marine-Earth Science and Technology and Hokkaido University propose that “these exoplanets may be more capable of supporting life because their ‘tidal locks’ can facilitate a moderate local thermal environment by redistributing heat flux laterally.”
Why Are Tidally Locked Exoplanets So Common?
This research challenges the widely-held belief that planets uniformly show one face to their stars. According to Noto, planets and moons that maintain constant day and night are far more prevalent than Earth-like planets that experience day-night cycles.
“Celestial bodies close to their parent stars often become tidally locked,” he explains. “As they rotate and orbit, their rotational speed synchronizes with their orbital period, resulting in a phenomenon where we only see one side of the moon.”
This fixed orientation leads to dramatic temperature contrasts across the planet. Rather than just focusing on surface conditions, researchers sought to explore the internal dynamics of these planets, particularly the mantle—the thick layer of rock situated between the crust and core.
Recreating an Alien Planet in the Laboratory
Instead of relying solely on computer simulations, the research team constructed a physical laboratory model simulating the interior of a tidally locked planet.
“Creating an actual exoplanet in the lab wasn’t feasible,” jokes Noto.
Instead, the researchers utilized a rectangular tank filled with viscous glycerol and tiny thermochromic liquid crystals that change color with temperature variations. This experimental setup is used to study heat transfer in slowly moving materials, simulating the rocky interiors of planets.
Unlike weather or ocean currents influenced by Earth’s rotation and gravity, convection within the rocky mantle arises mainly from differences in temperature and density. To emulate these conditions, the team installed four thermostats around the tank, heating and cooling different areas to create temperature gradients akin to those found on a tidally locked exoplanet.
Planetary Heat Engine
The experiments revealed a remarkably stable pattern. Hot material consistently rose beneath the dayside, flowed across the upper region, cooled on the nightside, and sank, creating a continuous circulation loop akin to the planet’s steady heartbeat.
“Unlike Earth’s chaotic mantle, this system is slow and steady,” Noto observes. “It’s predictable and, while a bit monotonous, in a positive way.”
Researchers also noted occasional mushroom-shaped plumes rising from the heated tank’s base. Differing from volcanic hotspots on Earth, these plumes remained fixed in place rather than drifting over time.
Measurements of heat transport, known as the Nusselt number, were comparable to those observed in Earth’s mantle. This suggests that some tidally locked exoplanets could maintain local geothermal environments conducive to life, particularly in their warmer mid-latitudes.
What Does This Mean for Alien Life?
Stable circulation patterns can influence more than just surface temperatures. Noto posits that this may also impact the movement of the planet’s liquid core, potentially generating a magnetic field distinct from Earth’s familiar dipole field.
“While we couldn’t test this in our experiment, it opens up exciting avenues for future research,” he adds.
See Beyond the Rest of the World
Noto and Ulloa are dedicated to advancing laboratory models to investigate various geophysical processes. Previous research from the Penn GEFLOW Institute has explored how heat and mass transfer in confined spaces can clarify the role of fluids in hydrothermal systems.
“We plan to broaden our experimental methods to probe deeper into diverse systems on Earth under varying contexts. The possibilities are truly out of this world,” states Noto.
Daisuke Noto is a postdoctoral fellow in the College of Arts and Sciences at the University of Pennsylvania.
Hugo Ulloa is an assistant professor in the Department of Earth and Environmental Sciences at Penn State College of Arts and Sciences.
Other contributors include Takehiro Miyakoshi and Takatoshi Yanagisawa from the Japan Agency for Marine-Earth Science and Technology, alongside Tomomi Terada and Yuji Tasaka from Hokkaido University.
Source: www.sciencedaily.com