Stop me if you’ve heard this one before, but astronomers just found a planet around Barnard’s star, which at about six light-years away is the second closest stellar system to the sun.It’s not the first time: claims of planets orbiting Barnard’s star have cropped up repeatedly for more than a half-century, only to be debunked. But this one, reported in the journal Astronomy and Astrophysics, appears to be on more solid footing. That’s because the researchers behind the study spent years lavishing the star with attention from one of Earth’s most advanced planet-hunting instruments, mindfully avoiding many of the pitfalls that undermined their predecessors. That work, in fact, has produced more than just one newfound world; tentative suggestions of three more candidate planets lurk within their data.“We have been collecting data from 2018 until now on this star,” says Jonay I. González Hernández, a staff research scientist at Institute of Astrophysics of the Canary Islands and lead author of the paper. The team’s efforts focused on the star’s so-called habitable zone, a circumstellar region in which starlight could sufficiently heat a planet to allow liquid water to exist on its surface. At first, the researchers saw nothing. “But as we got more and more data,” González Hernández says, “we realized something was starting to appear.”On supporting science journalismIf you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Just because a world resides in a star’s habitable zone, however, doesn’t mean it’s a nice place to live. For instance, the confirmed planet and its three candidate companions are all estimated to be less massive than Earth—meaning they could have a harder time holding on to an appreciable atmosphere. The confirmed planet is also apparently the biggest, at nearly 40 percent the weight of our world, while the three candidates range between estimated masses of around one fifth to one third that of Earth. For comparison, Venus weighs in at just more than 80 percent of Earth’s mass, Mars is a mere tenth of our planet’s weight, Mercury is much lighter, and Neptune, Uranus, Saturn and Jupiter are all far heavier. That means the masses of these possible Barnard’s star worlds place them in a planetary class unknown to our familiar solar system. Astronomers have found similar oddballs before: a handful of so-called super-Jupiters, and oodles of super-Earths orbiting alien suns. Now, apparently, they’ve found a “super-Mars” system, too, around one of our nearest stellar neighbors.Like the existence of the three candidates themselves, however, the planets’ super-Mars statuses could be illusory. The radial-velocity technique—which is used to uncover these and many other possible worlds—can only set lower limits on any putative planet’s mass. That’s because the method only indirectly infers the presence of planets by measuring how their gravitational tug makes a star wobble to and fro along our line of sight as they twirl around it. The larger the wobble, the heftier the world responsible for it. But if the planet’s orbit around its star isn’t seen “edge on” from Earth, radial-velocity measurements will only reveal a fraction of its full pull. Even for giant planets, this wobble is tiny, on the order of hundreds of meters of motion per second for an entire star.As tiny as that seems, the wobbles of small worlds usually manifest as motions approximately 10 times smaller still. Astronomers discern such subtleties by using a spectrograph to split a star’s light into its constituent colors, looking for Doppler shifts in the rainbowlike spectrum. Instantaneous detections are rare; instead evidence of a wobble gradually builds over weeks, months or even years of observing time as planets complete their orbit. Astronomers have employed the method for planet hunting since the 1980s, and researchers used it to discover and confirm the first exoplanet around a sunlike star in 1995.The study’s confirmed planet orbits Barnard’s star in 3.15 Earth days, while the three candidates appear to have respective orbits of 4.12, 2.34 and 6.74 days. The team behind the study relied on the Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) instrument located at the Very Large Telescope in Chile. ESPRESSO is an astonishingly sophisticated piece of hardware, able to reach precisions unimaginable 30 years ago.“From the beginning, our priorities were to search for Earth-like planets orbiting nearby stars,” says González Hernández. In 2022 the same team also reported a detection of a small planet around our solar system’s nearest neighboring star, Proxima Centauri (itself part of Alpha Centauri, the multi-star system that is closest to us). ESPRESSO’s success in finding such small planets is a promising sign for the future of the radial-velocity technique, suggesting that even more diminutive worlds may yet be within its reach.“It is quite impressive how they managed to pull out the signals because this new instrument reached a level of precision that we couldn’t do before,” says Mercedes López-Morales, associate director for science at the Space Telescope Science Institute.López-Morales, who was not involved in the study, admits she was skeptical when she first read the paper, especially because of how minuscule the wobbles were for the claimed planet and its candidate kin alike. But as she dove into the methodological details that sought to shore up the soundness of its measurements, she became convinced of the work’s strengths.“I still do think that [the researchers] need a lot more data, but the analysis looks pretty solid to me,” she says.López-Morales, who studies atmospheric dynamics of exoplanets, says that these planets are unlikely to have an atmosphere because of their close proximity to their host star. Barnard’s star is only about 16 percent of the mass of the sun—a so-called M dwarf star that shines far fainter than our own. Despite their small size, though, M dwarfs are also prone to violent outbursts in the first few million years of their existence, ejecting monstrous flares that can strip the atmospheres from any planets in their way. With no atmosphere, such worlds offer no chance for liquid water—life’s cornerstone—to persist on their surface. The 3.15-day orbit of the new study’s confirmed planet, however, makes it likely too hot to hold on to water anyway, even with an atmosphere. Some of the candidate worlds may be a little more temperate, according to the paper.Prior to these latest results, Barnard’s star has been associated with at least two controversial planetary claims—one from the 1960s that was ultimately traced to optical flaws in a telescope and another in 2018 that was subsequently shown to instead be run-of-the-mill stellar activity arising from the star’s rotation. This freshly confirmed planet and the planetary candidates are different, with wobbles well below the rotation rate of 145 days for Barnard’s Star and thus less likely to be spurious results of stellar activity.Suvrath Mahadevan, an astronomer at Pennsylvania State University and co-author of a paper that cast grave doubts upon the 2018 claim, notes that the latest ESPRESSO data “completely confirm that assertion.” Precisely for this reason, though, he deems the instrument’s measurements of a notional 3.15-day wobble to be of a higher caliber. “I would say the [3.15-day] planet looks compelling to me; the data look exquisite,” says Mahadevan, who wasn’t part of the study.Other independent observations already exist that could imminently aid in the hunt, including data gathered at the Arecibo Observatory in Puerto Rico prior to its destruction and subsequent decommissioning.“We possess several years of observational data on Barnard’s star, collected via the Arecibo Observatory, which provides an opportunity to search for periodic signals corresponding to a three-day orbit,” says Abel Méndez, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. Mendez, who was not involved in the new ESPRESSO study, is also intrigued by the tantalizing hints of other worlds there, which suggest “the possibility of a highly compact planetary system.” Scientists are still struggling to understand exactly how such planetary systems form, in part because they are so alien from our own. Finding one that, in galactic terms, is practically next door could offer a front-row seat on a natural laboratory to scrutinize for future breakthroughs.