Barnard's Star, just some 6 light-years away, has intrigued astronomers for over a century.
Does the second-closest stellar system to us host any planets?
Though this system has hoodwinked astronomers with planetary signals before, researchers say they're confident they have detected three new planets and confirmed another. After peering at Barnard's Star over 112 nights, scientists using a powerful telescope in Chile found compelling evidence of four particularly small exoplanets, each just some 20 to 30 percent the size of Earth. That makes them considerably smaller than Mars, which is about half Earth's size.
"It’s a really exciting find — Barnard’s Star is our cosmic neighbor, and yet we know so little about it," Ritvik Basant, an exoplanet researcher at the University of Chicago who led the research, said in a statement. "It’s signaling a breakthrough with the precision of these new instruments from previous generations."
The new research has been published in The Astrophysical Journal Letters.
Each of these worlds is probably rocky, as opposed to a gas giant planet like Jupiter, but they almost certainly aren't habitable. That's because they're searing hot, as they zip closely around Barnard's Star in just a matter of days. Even so, their discovery shows new ways that astronomers can find such small, nearly imperceptible worlds, known as "sub-Earths."
It was tremendously challenging to detect these planets. For one, they're located right next to their luminous star, making them daunting to see. And from our perch on Earth, we don't see these worlds transiting in front of their star, which is a common way planets beyond our solar system, or exoplanets, are found.
To find these worlds, the astronomers used something called the radial velocity technique, wherein a specialized instrument on a telescope looks for a star exhibiting extremely slight wobbles. These wobbles are caused by the gravitational influence, however small, orbiting planets have on their star, which subtly alters the star's emitted light. (In this case, a high resolution instrument called MAROON-X was mounted on the over 26-foot-wide Gemini North telescope, located at 8,930 feet in the profoundly dark Chilean desert.)
"The powerful instrument measures these small shifts in light so precisely that it can even tease apart the number and masses of the planets that must be circling the star to have the observed effect," the National Science Foundation's NOIRLab — which runs big telescopes across the U.S. and globally — said in a statement.
Astronomers are keenly interested in understanding planets around stars like Barnard's, which is a red dwarf. These are small stars, but the most common in the universe. Importantly, red dwarfs are cooler than more massive stars, meaning they can host habitable zones (regions of a solar system that are temperate enough for worlds to harbor liquid water) close to themselves, where planets often form. Scientists are also using the James Webb Space Telescope to discern if such rocky worlds around red dwarfs could host atmospheres, like Venus or Earth.
If Barnard's Star was hiding four rocky sub-Earths, what else is hiding out there in the cosmos?
