May 30, 2024


Astronomers have discovered a new Earth-sized planet orbiting a small, cool star expected to shine 100 times longer than the sun.

The rocky world, called Speculoos-3b, is 55 light-years from Earth and was detected as it passed in front of its host star, an ultracool red dwarf half as hot as the Sun and 100 times less luminous.

The newly discovered world, described as “practically the same size as our planet”, swings around the red dwarf once every 17 hours, making a year on the planet shorter than a single Earth day.

But while the years are short on Speculoos-3b, the days and nights are never-ending. “We believe that the planet rotates synchronously, so that the same side, called the day side, always faces the star, just as the moon does for the Earth. On the other hand, the night side’s hand would be locked in endless darkness,” said Michael Gillon, an astronomer at the University of Liège in Belgium and lead author of the study.

It is only the second planetary system discovered around such a star, following the detection of seven rocky worlds around Trappist-1, another cool red dwarf star 40 light-years from Earth.

Researchers spotted the planet as it wandered across the face of its star, causing the starlight to dim. The transit was tracked by the Speculoos (Search for Planets EClipsing ULTra-cOOl Stars) global network of robotic telescope.

Ultra-cool red dwarf stars make up about 70% of the stars in our galaxy and survive for about 100 billion years, making them the last stars to shine in the universe. Because they are so faint and scattered across the sky, astronomers must observe them over several weeks to detect planets crossing in front of them.

The long lifetimes of red dwarf stars mean planets orbiting them can be hot enough for long enough for life to emerge. But in the case of Speculoos-3b, any life would face an extremely harsh environment. The planet’s tight orbit means it is bombarded with radiation and receives nearly 16 times more energy per second than Earth.

“In such an environment, the presence of an atmosphere around the planet is highly unlikely,” said Julien de Wit, a planetary scientist at MIT and co-director of the Speculoos Northern Observatory and its Artemis telescope.

Details are published in Nature Astronomy.



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