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Barnard’s Star Finally Has a Planet, and Possibly More
For a century, exoplanet hunters have “discovered” planets around a nearby star, only to retract the claims. But the latest find is for real.
Barnard’s Star is a dim, reddish ball of gas just six light-years away from Earth in the constellation Ophiuchus. It is the nearest stand-alone star to our sun, but with only one-fifth the mass, it is so dim that no one knew it was there until 1916, when the astronomer Edward Emerson Barnard recorded its image on a photographic plate.
Ever since, astronomers have been “discovering” planets around Barnard’s Star, but none have withstood verification. Now, one planet — and maybe more — has been confirmed.
In 1963, long before the search for exoplanets became a respectable endeavor, Peter van de Kamp, a Dutch astronomer at Swarthmore College’s Sproul Observatory in Pennsylvania, announced that Barnard’s Star had a planet. Astrometric measurements, he said, showed that the star wobbled in its path across the sky. Dr. van de Kamp attributed the wobble to the gravitational tug of a planet with the mass of Jupiter.
The claim made headlines, but nobody else could replicate the finding. The wobble was eventually traced not to a planet but to anomalies in the 24-inch telescope.
But as Paul Butler, an astronomer with the Carnegie Institution for Science, told The Washington Post, Barnard’s Star is “the great white whale” of exoplanet hunts.
Dr. Butler was part of a team in 2018 that announced having found a much smaller planet orbiting Barnard’s Star, as part of what they called the Red Dots campaign. Barnard Star b, as the entity was designated, was about three times as massive as Earth and circled the star every 233 days — but at too great a distance to be warmed sufficiently to support life.
The team, led by Ignasi Ribas of the Institute of Space Studies of Catalonia in Spain, deduced the presence of this planet by measuring a regular speedup and slowdown in the velocity of Barnard’s Star as the supposed planet orbited it, tugging the star backward and forward.
“After a very careful analysis, we are 99 percent confident that the planet is there,” Dr. Ribas said at the time in a statement issued by the European Southern Observatory.
Barnard b has not been seen again.
Red dwarfs like Barnard’s Star are happy hunting grounds for planet chasers: They are not only the most common stars in the universe but also the most easily wobbled by their planets, especially if the planets circle closely, with orbital periods of just a few days.
For the last five years another team based at the European Southern Observatory has undertaken a systematic search for such planets around Barnard’s Star. It used the best equipment available: an 8.2-meter diameter telescope at ESO’s Paranal Observatory in Chile and a fancy spectrograph called ESPRESSO, which could detect changes in the star’s velocity as slight as a couple of feet per second.
In October the team announced that it had hit pay dirt: one new planet, half as massive as Venus, that circled the star every three days. It also detected hints of three other planets hugging Barnard’s Star; those results await confirmation.
In keeping with astronomical convention, the astronomers have named the new planet Barnard b. “Even if it took a long time, we were always confident that we could find something,” Jonay González Hernández, a researcher at the Instituto de Astrofísica de Canarias in Spain and lead author of the paper, said in a statement issued by the European Southern Observatory.
“All of them are smaller than Earth,” Dr. Hernandez noted in an email. He added that none were likely to be habitable; they all orbit the star inside the Goldilocks band in which the planet’s surface temperature could support liquid water. The newly confirmed planet — one of the smallest exoplanets yet found — should have a temperature of about 125 degrees Celsius, above water’s boiling point. The temperature of even the outermost of Barnard b’s possible planets would be about 50 degrees Celsius higher than the average temperature on Earth, Dr. Hernández said.
The work confirms scientific expectations that the nearby cosmos is brimming with planets. In the last few years, astronomers have discovered three small rocks circling Proxima Centauri, part of a triplet star system even closer to us than Barnard’s Star, only about four light-years away. But researchers have seen no sign of the previous Barnard b with a 233-day orbit.
“It seems quite improbable that the planet candidate we claimed in 2018 is indeed there,” Dr. Ribas told Sky and Telescope magazine in October. The ESPRESSO instrument that Dr. Hernández’s team had is far more precise than what the spectrometers used in their 2018 paper. The newly proposed planet qualified as “a solid detection,” Dr. Ribas added.
It’s three steps forward, one step back in the hunt for cosmic real estate.
Dennis Overbye is the cosmic affairs correspondent for The Times, covering physics and astronomy. More about Dennis Overbye
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