4 Tiny Planets Found Orbiting Earth's Closest Solitary Star

Just 5.96 light-years from Earth sits Barnard’s Star, a red dwarf with a fifth of the Sun’s diameter and even less of its mass. Considered a solitary star for its lack of stellar companions, Barnard’s Star is notoriously lonely—signs of any exoplanets in its orbit have come and gone without reliable evidence. But today, astronomers know the star is in good company. Four tiny worlds have been found in the star’s orbit, each with just a fraction of Earth’s mass.
An international team of researchers announced their first clues last year, when five years of observations through the European Southern Observatory’s (ESO) Very Large Telescope (VLT) yielded signs of a sub-Earth mass exoplanet. The team initially sought exoplanets in Barnard’s Star’s habitable zone, or the distance from the star where a planet can sustain liquid water (if it has any). Instead they found Barnard b, an exoplanet with half the mass of Venus that orbits twenty times closer to Barnard’s star than Mercury orbits the Sun.
Since then, Barnard b’s existence has been confirmed—and so has the presence of three additional exoplanets in Barnard’s Star’s neighborhood. In a new paper for The Astrophysical Journal Letters, astronomers at the University of Chicago, Hawaii’s Gemini Observatory, and the University of Amsterdam describe all four exoplanets, which orbit their star in quick, snug circles.
Joining Barnard b are Barnard c, d, and e, whose years last anywhere from 2.3 Earth days (Barnard d) to 6.7 Earth days (Barnard e). These orbits are too quick to make any of them habitable: Even if Barnard’s Star is cooler than our Sun, the exoplanets’ proximity to the star would make them too hot for life. The planets are slight, too. Barnard c’s mass is just a third of Earth’s; Barnard d has a quarter of Earth’s mass, and Barnard e has a fifth. 
To find exoplanets that small, researchers in Chicago built an instrument that attaches to a telescope at the Gemini Observatory and hunts down shy, distant worlds. Called MAROON-X, the instrument looks for the almost imperceptible stellar “wobble” that results from an exoplanet’s gravitational tug on its star. By keeping a close eye on the light emanating from that star, MAROON-X detects minute changes that signal an exoplanet’s presence. Depending on the type of wobble it catches, MAROON-X can even help determine an exoplanet’s mass.
Researchers in Europe used the VLT’s ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) to double-check MAROON-X’s findings. 
“We observed at different times of night on different days. They’re in Chile; we’re in Hawaii. Our teams didn’t coordinate with each other at all,” said first study author Ritvik Basant. “That gives us a lot of assurance that these aren’t phantoms in the data.”
The solidity of the team’s MAROON-X and ESPRESSO data also suggests with a “fair degree of certainty” that no other exoplanets exist in Barnard’s Star’s orbit. Still, the fact that planetary companions have finally been confirmed is groundbreaking, as are the technologies that helped to find them.
“It’s a really exciting find—Barnard’s Star is our cosmic neighbor, and yet we know so little about it,” Basant said. “It’s signaling a breakthrough with the precision of these new instruments from previous generations.”
© 2001-2025 Ziff Davis, LLC., a Ziff Davis company. All Rights Reserved.
ExtremeTech is a federally registered trademark of Ziff Davis, LLC and may not be used by third parties without explicit permission. The display of third-party trademarks and trade names on this site does not necessarily indicate any affiliation or the endorsement of ExtremeTech. If you click an affiliate link and buy a product or service, we may be paid a fee by that merchant.

source