An international team of astronomers has discovered an Earth-sized exoplanet where the sun never sets on one side and never rises on the other. Orbiting an ultracool dwarf star just 55 light-years away, this planet completes its orbit in only 17 hours.
Dubbed SPECULOOS-3b, the planet is tidally locked, meaning the same side always faces its star, resulting in perpetual daylight on one side and endless night on the other. This discovery marks the second planetary system found around such a star, following the TRAPPIST-1 system.
SPECULOOS-3, the star, is an ultracool dwarf similar in size to Jupiter but much cooler, with a mass ten times smaller and luminosity a hundred times weaker than our Sun. Despite their longevity and prevalence, little is known about planets orbiting these faint stars due to their low brightness.
Michael Gillon, lead author of the study published in Nature Astronomy, noted, “SPECULOOS-3b is practically the same size as our planet. We believe the planet is tidally locked, with the same side always facing the star.”
The discovery was made by the SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars) project, led by Gillon at the University of Liège. The project uses a global network of robotic telescopes to observe nearby ultracool dwarfs for transiting planets. Laetitia Delrez, a researcher on the project, mentioned that SPECULOOS was designed to find rocky planets around these stars for detailed study. In 2017, their prototype discovered the TRAPPIST-1 system with seven Earth-sized planets.
SPECULOOS-3b, though inhospitable to life as we know it, provides a unique opportunity to study a rocky exoplanet’s surface. The intense radiation from its star likely means it has no atmosphere. This planet is an ideal target for the James Webb Space Telescope, which can analyze its surface composition.
The team plans to expand the SPECULOOS network to accelerate the search for these intriguing alien worlds.
