Meet the First Planet with a Permanent Dark Side

In a groundbreaking discovery, scientists have found the first planet outside our solar system that has a permanent "dark side" that is always in night-time and a perpetually daytime side. This phenomenon, known as 1:1 tidal locking or tidal synchronization, has been theorized for many exoplanets but has not been confirmed until now.

The planet, called LHS 3844b, is a "super-Earth" located 48.6 light-years away from Earth. It is eight times the mass of Earth and orbits its star in just 11 hours. Its proximity to its star makes it an ideal candidate for studying tidal locking.

Using data from the Spitzer Space Telescope, researchers from McGill University in Montreal, Canada, analyzed the intensity of light coming off the planet's surface. They found that the surface temperature of LHS 3844b was relatively cool, which suggests that the planet is tidally synchronized.

"This is the most compelling evidence one could possibly gather with currently existing information or instrumentation," said Emily Rauscher, a theoretical astrophysicist at the University of Michigan.

While the study assumes that LHS 3844b has no atmosphere, a 2022 study left room for a thin, Earth-like atmosphere. If the planet does have an atmosphere, it could complicate the argument for tidal synchronization. However, the evidence presented in the study points to tidal synchronization.

The discovery of LHS 3844b's tidal synchronization has significant implications for the study of exoplanets and the search for habitable worlds. The James Webb Space Telescope (JWST), set to launch later this year, will allow astronomers to study the rotation of exoplanets that are further away from their stars than LHS 3844b. These planets, which can sustain an atmosphere and mild temperatures, constitute most of the Milky Way's habitable real estate.

"If the JWST finds them to be tidally synchronized like LHS 3844b, then probably a good fraction of planets, certainly most habitable planets, are tidally locked," said Nicolas Cowan, an astronomer at McGill University and co-author of the study.

The discovery of LHS 3844b's tidal synchronization is an exciting development in the study of exoplanets. As scientists continue to explore the universe for habitable worlds, the study of tidal synchronization will be crucial in understanding the conditions necessary for life to thrive.

Sources:

1. Lyu, X. et al. (2024). "Evidence for 1:1 Tidal Locking of the Super-Earth LHS 3844b". Astrophys. J. 964, 152.
2. Kreidberg, L. et al. (2019). "Absence of a Thermal Emission Signal From the Super-Earth 55 Cancri e". Nature 573, 87–90.
3. Whittaker, E. A. et al. (2022). "Transit Timing Variations and the Composition of the Sub-Neptune-Sized Planets Orbiting HD 119642". Astron. J. 164, 258.