Astronomers discover Earth-sized planet with eternal days and nights

Astronomers have discovered a new Earth-sized planet just 55 light-years away, orbiting an ultra-cool red dwarf star. The findings were published in Nature Astronomy. This planet is only the second of its kind found around this type of star.

Named SPECULOOS-3 b, the planet completes an orbit in approximately 17 hours, making a year on the planet shorter than a single Earth day. The star it orbits is more than twice as cool as our sun, being ten times less massive and one hundred times less luminous. According to the researchers, SPECULOOS-3 b experiences endless days and nights.

Michaël Gillon, an astronomer at the University of Liège in Belgium and the lead author of the study, explained to phys.org that the planet likely rotates synchronously, meaning the same side, known as the day side, always faces the star, while the night side remains in perpetual darkness, similar to the moon’s relationship with Earth.

Ultra-cool red dwarf stars, which make up about 70% of all stars in our galaxy, have lifespans of around 100 billion years, potentially making them some of the last stars to shine in the universe. Due to their faintness and scattered distribution, astronomers must monitor these stars for several weeks to detect planets transiting in front of them.

The discovery was supported by the SPECULOOS project, led by the University of Liège in collaboration with the Universities of Birmingham, Cambridge, Bern, and the Massachusetts Institute of Technology. SPECULOOS, which stands for Search for Planets EClipsing ULtra-cOOl Stars, uses robotic telescopes worldwide to search for potentially habitable exoplanets around the smallest and coldest stars in our solar neighborhood.

Gillon noted, “We designed SPECULOOS specifically to observe nearby ultracool dwarf stars in search of rocky planets that lend themselves well to detailed studies.”

He added, “In 2017, our SPECULOOS prototype using the TRAPPIST telescope discovered the famous TRAPPIST-1 system, which consists of seven Earth-sized planets, several of which are potentially habitable. This was an excellent start.”