Barnard's Star and Exoplanets
An artist’s rendering of Barnard’s Star, as seen from one of the newly discovered exoplanets orbiting it International Gemini Observatory / NOIRLab / NSF / AURA / P. Marenfeld under CC BY 4.0
For decades, astronomers have probed the space around Barnard’s Star in search of exoplanets. As our cosmic neighbor—the nearest single-star system to our sun—it’s been a tempting place to look. In 1963, Dutch scientist Peter van de Kamp claimed to have discovered the first exoplanet orbiting the red dwarf star, but the discovery was later found to be an error related to disturbances in his telescope.
The search continued, however, and Barnard’s Star has since been dubbed “the great white whale” for exoplanet seekers, as Paul Butler, an astronomer at Carnegie Science’s Earth and Planets Laboratory, told the Washington Post’s Sarah Kaplan in 2018.
But in October, astronomers revealed the existence of a single tiny, rocky planet orbiting the star. And now, another study has found evidence of four. The new results were published last week in The Astrophysical Journal Letters.
“Finally, real planets have been discovered around Barnard’s Star after several false alarms over the past [50 years],” Edward Guinan, an astronomer at Villanova University who was not involved in the new study, tells CNN’s Ashley Strickland.
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Barnard’s Star is small—about 15 percent the mass of our sun—and only around six light-years away. Despite its proximity, though, it’s too faint to see in the night sky without a telescope or strong binoculars.
To find the tiny planets orbiting it, then, astronomers turned to a technique called the radial velocity method. This approach measures slight wobbles in the motion of distant stars. From these variations, astronomers can infer the presence of small planets tugging on their star—and even discern the planets’ mass.
In the new study, astronomers combined data from the MAROON-X spectrograph attached to the Gemini North Telescope in Hawaii and the ESPRESSO spectrograph on the Very Large Telescope in Chile. Separate teams collected data on the two instruments independently and combined their results to identify the exoplanets.
“We observed at different times of night on different days,” lead author Ritvik Basant, an astronomer at the University of Chicago, says in a statement. “They’re in Chile; we’re in Hawaii. Our teams didn’t coordinate with each other at all. That gives us a lot of assurance that these aren’t phantoms in the data.”
MAROON-X
A scientist works to assemble the MAROON-X spectrograph in 2019 at the Gemini North Telescope in Hawaii. International Gemini Observatory / NOIRLab / NSF / AURA / A. Peck under CC BY 4.0
The technology to measure subtle changes in a star’s motion with high precision has improved drastically in recent years, enabling discoveries such as this one. “The instruments have grown to give an unprecedented precision in radial velocities,” Basant tells Scientific American’s Tom Metcalfe.
The four newly discovered exoplanets are small—each about 20 to 30 percent of Earth’s mass—and likely to be rocky, rather than gaseous. They all orbit Barnard’s Star closer than Mercury orbits the sun. This closeness means they’re likely too hot and were historically too exposed to solar radiation, flares and dense winds to host any living organisms.
“Because of this, these sub-Earth size planets probably don’t have atmospheres, water and life,” Guinan tells CNN.
But astronomers are hopeful that this finding is just the start of a new era of exoplanet discovery.
“A lot of what we do can be incremental, and it’s sometimes hard to see the bigger picture,” study co-author Jacob Bean, an astronomer at the University of Chicago, says in the statement. “But we found something that humanity will hopefully know forever. That sense of discovery is incredible.”