New Earth-sized exoplanet found with mysterious ultra-cool dwarf star

(CN) — Scientists do not know much about the stars that will last until the end of the universe.

According to a study published Wednesday in Nature Astronomy, ultra-cool dwarf stars are the least massive stars in the universe, similar in size to Jupiter. But these stars possess a lifespan over a hundred times longer than that of Earth’s sun, meaning that ultra-cool dwarf stars will be the last ones to shine when the rest of the universe becomes cold and dark.

However, while ultra-cool dwarf stars are far more common in the cosmos than sun-like stars, the study says that scientists do not fully understand them due to their low luminosity. There is even less known about the stars' planets, despite the fact that they comprise a significant portion of our galaxy's — the Milky Way — planetary population.

Determined to uncover more information about these planets, the Universities of Liège, Cambridge, Birmingham, Berne, MIT and ETH Zürich created the Search for Planets EClipsing ULtra-cOOl Stars (“SPECULOOS”).

“We designed SPECULOOS specifically to observe nearby ultra-cool dwarf stars in search of rocky planets that lend themselves well to detailed studies,” said Laetitia Delrez, an astronomer at the University of Liège. “In 2017, our SPECULOOS prototype using the TRAPPIST telescope discovered the famous TRAPPIST-1 system made up of seven Earth-sized planets, including several potentially habitable ones. This was an excellent start!”

After this, the researchers found a new Earth-sized planet orbiting a nearby ultra-cool dwarf star. According to the study, SPECULOOS 3 is only the second planetary system discovered around this type of star. The SPECULOOS-3 b exoplanet is around 55 light-years away from Earth, which on a cosmic scale is quite close since the Milky Way stretches over 100,000 light-years.

First author of the study Michaël Gillon revealed more details about the exoplanet’s movements.

“A year, i.e. an orbit around the star, lasts around 17 hours,” said Gillon, a University of Liège astronomer who initiated and led SPECULOOS. “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.”

As for the SPECULOOS-3 star, the study said that it is over twice as cool as Earth’s sun with an average temperature of 4,712 degrees Celsius, and its hyper-short orbit gives its exoplanet almost 16 times more energy per second than what Earth gets from its sun.

“In such an environment, the presence of an atmosphere around the planet is highly unlikely,” said Julien de Wit, MIT professor and co-director of the SPECULOOS Northern Observatory and its Artemis telescope, a collaboration between the Universities of Liège and MIT, which the study called the mainstay of this discovery. “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.”

Emboldened by their discovery, Gillon said that he and the team intend to continue their hunt for more planets.

“This discovery demonstrates the ability of our SPECULOOS-North observatory to detect Earth-sized exoplanets suitable for detailed study,” said Gillon. “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.”

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