Astronomers have identified 4 exoplanets orbiting the nearest single star to Earth, an effort that had been ongoing for 50 years and produced many false positives.
These rather small planets are a stone’s throw from Earth in galactic terms, but were too small for previous instruments to detect.
Barnard’s Star is a low-mass red dwarf star just 6 light-years from Earth discovered in 1916, and astronomers have long wondered if there could be planets orbiting it just like there are in our solar system.
There are two conventional ways to look for exoplanets. The first is the transiting technique, whereby a telescope will look for detectable drops in the level of light from a star caused by an exoplanet passing between the telescope and the star. However, the planets around Barnard’s Star, and likely many, many others in the Milky Way, are too small to reduce the level of light as we see it with today’s observatories.
So instead, astronomers can use the radial velocity method which looks for “wobbles” in the star’s position caused by the gravity of an orbiting exoplanet gently tugging at it during close approaches.
“It’s a really exciting find—Barnard’s Star is our cosmic neighbor, and yet we know so little about it,” said lead study author Ritvik Basant, doctoral student of astronomy and astrophysics at the University of Chicago, in a statement cited by CNN. “It’s signaling a breakthrough with the precision of these new instruments from previous generations.”
The worlds are referred to as sub-Earths, meaning they have a much lower mass than Earth, in this case between 19% and 34% of our planet’s total size. They are likely uninhabited rocks due to their positioning around their star.
“When compared to our solar system, each of the four planets are inside the distance of Mercury’s orbit,” Basant said.
That means on the closest one, it takes just 3 days to complete a year, and even the farthest one takes 7.
They were detected using the radial velocity method with MAROON-X, an instrument mounted on the Gemini North telescope in Hawaii that’s designed to search for exoplanets around red dwarf stars, the smallest kind of living star.
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The star has likely been blasting them with X and UV radiation, solar wind, and other harmful forces that would have scoured any water or atmosphere, and so there’s not much point looking for signs of life there, or even as a thought exercise of interstellar human migration.
Instead, and perhaps contrary to intuition, these sorts of sub-Earths are believed to be more highly varied in composition than larger worlds, of which well over 5,000 have been officially documented.
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Accordingly, these and other small planets like them should help expand our understanding of all the possibilities of planetary formation.
The study was published in the Astrophysics Journal Letters.
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