Discovery of an Earth-sized planet challenges our understanding of ultracool dwarfs
Astronomers from Belgium have made a discovery that could contribute to a deeper understanding of the universe. They observed a planet of Earth-like size near an ultracool dwarf star situated 55 light-years away from us. This star is half as cold as our Sun, but the earth close to it is exposed to intense radiation.
This discovery is the responsibility of the research team from the University of Liège, leading the SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars) project. The experts identified a planet named SPECULOOS-3 that orbits the ultracool dwarf. This is the second planetary system discovered around such a star.
A planet of Earth-like size
Ultracool dwarfs, as explained by scientists, are the most miniature massive stars in the universe. Their sizes are comparable to giant planets like Jupiter. They are half as cool as the Sun, have a mass 90% less than the Sun’s, and are about 100 times dimmer. Moreover, they live about 100 times longer than our daytime stars and will be the last to survive in the future cooling universe.
Despite being more numerous in space than stars like the Sun, ultracool dwarfs are poorly understood because they emit only a tiny amount of light. In particular, little is known about the planets that orbit them, even though they are believed to constitute a significant portion of all Milky Way planets.
The SPECULOOS project, coordinated by Prof. Michaël Gillon from the University of Liège, was created to search for planets orbiting ultracool dwarfs. Scientists look for planets passing in front of the star, which allows their detection but usually requires weeks of observation for each star individually. Therefore, the project’s creators use a network of automated telescopes to speed up the observation process significantly.
The newly discovered planet, named SPECULOOS-3 b, is located 55 light-years from our Solar System. So, we can say that it is our cosmic neighbour. "SPECULOOS-3 b is practically the same size as our planet," emphasizes Michaël Gillon, the author of the paper published in the journal "Nature Astronomy."
"A year, i.e. an orbit around the star, lasts around 17 hours. Days and nights, on the other hand, should never end. We believe that the planet rotates synchronously, so that the same side, called the day side, always faces the star, just like the Moon does for the Earth. On the other hand, the night side hand, would be locked in endless darkness," explains the planetologist.
Although the star around which the planet orbits is relatively cold, the very close orbit means the planet is bombarded with high-energy radiation. "In such an environment, the presence of an atmosphere around the planet is highly unlikely," notes Prof. Julien de Wit from MIT, who is involved in the project.
"The fact that this planet has no atmosphere could be a plus in several respects. For example, it could enable us to learn a great deal about ultra-cool dwarf stars, which in turn will make possible more in-depth studies of their potentially habitable planets," he adds.
According to researchers, SPECULOOS-3 is an excellent target for the James Webb Telescope. "With the JWST, we could even study the mineralogy of the planet's surface!" emphasizes Dr. Elsa Ducrot, co-author of the discovery.
"This discovery demonstrates the ability of our SPECULOOS-North observatory to detect Earth-sized exoplanets suitable for detailed study. And this is just the beginning! Thanks to the financial support of the Walloon Region and the University of Liège, two new telescopes, Orion and Apollo, will soon join Artemis on the plateau of the Teide volcano in Tenerife to speed up the hunt for these fascinating planets," concludes Prof. Gillon.
