Astronomers are reporting the discovery of SPECULATORS-3b, an Earth-sized planet that orbits an ultra cool dwarf, a star not much bigger than Jupiter. This is the only second known system such as this. The other one is the well-known TRAPPIST-1, which sports seven Earth-sized planets. The new system is 55 light-years away.
The star has a surface that is twice as cold as the Sun’s own, and that makes it about 1,000 times dimmer. But the planet is a lot closer to it than Earth is to the Sun. It goes around its star in just 17 hours and it is blasted by 16 times more radiation per second than our planet.
It's likely this is only on one side, because orbiting so close, the planet is expected to be tidally locked like the Moon is tidally locked to Earth. One side of SPECULOOS-3b is in perennial night while the other is in constant light. But this gives astronomers an opportunity to study it directly.
“We can say from our spectra and other observations that the star has a temperature of about 2,800 kelvins, it is about 7 billion years old – not too young, and not too old – and it is moderately active, meaning that it flares quite a lot,” co-author Benjamin Rack ham from MIT said in a statement. “We think the planet must not have an atmosphere anymore because it would easily have been eroded away by the activity of the host star that’s basically constantly flaring.”
While an atmosphere seems unlikely, there is an even more exciting possibility for this world. The team believes that by observing the planet going behind the star 10 times with JWST, they will be able to confirm whether it has an atmosphere or not. If it doesn’t, they might be able to study its rocks. And that would be a first.
“If there’s no atmosphere, there would be no blue sky or clouds – it would just be dark, like on the surface of the moon,” Rackham explained. “And the ‘sun’ would be a big, purplish-red, spotted, and flaring star that would look about 18 times as big as the sun looks to us in the sky.”
“SPECULOOS-3b is the first planet for which we can consider moving toward constraining surface properties of planets beyond the Solar System,” added study co-author Julien de Wit, associate professor of planetary sciences at MIT. “With this world, we could basically start doing ex planetary geology. How cool is that?”
Understanding the composition of a world in another solar system is extremely important. We could learn how similar or different rocky planets elsewhere are, and whether all of them have the ingredients that might make life. The star is also the most common type of star in the galaxy (70 percent of all the stars in the Milky Way) and it is supposed to live 10 times as long as our Sun. Understanding habitability conditions around it will tell us how likely life elsewhere is.
The study is published in the journal Nature Astronomy.
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