The most sensitive modern search rules out giant planets close to either star, but leaves room for smaller worlds in the habitable zones.
In 1855, the British astronomer William Jacob claimed to have detected a planet tugging on the stars of 70 Ophiuchi, a pair of suns about 16 light-years from Earth. It made the system the first host of an official exoplanet candidate. The claim did not hold up, and the system has teased astronomers ever since.
Now a study in The Astrophysical Journal, led by Yiting Li, a postdoctoral researcher in the University of Michigan’s Department of Astronomy, delivers the most sensitive modern verdict. There are no planets as massive as Jupiter, or larger, within 5 astronomical units of 70 Oph A or within 0.5 AU of 70 Oph B. One AU is the distance between Earth and the sun.
“It’s a mix of disappointment and excitement,” Li said. “We’re finding out that there isn’t a Jupiter-sized planet,” but, she added, “we’re also opening the latest chapter on this historic system.”
A hundred years of wobbles
70 Oph AB is the third-closest binary star system to Earth, after Alpha Centauri at about 4.2 light-years and 61 Cygni at about 11.4. The orbits of its two stars are among the best characterized in the sky, which makes the system an ideal laboratory for planet hunting.
The team combined roughly a century of radial velocity and astrometric measurements, which track how stars move toward and away from us and across the sky, with new observations from the 6.5-meter Magellan Clay Telescope at Las Campanas Observatory in Chile and the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory in Texas.
One signal had looked promising: a wobble in the stars’ radial velocity consistent with a Jupiter-sized companion. The team traced it instead to changes on the surfaces of the stars themselves.
“It’s a cautionary tale about how stellar activity can mimic planet signals using the radial velocity,” said Michael Meyer, senior co-author and chair of the U-M astronomy department. “Yiting assembled an absolutely huge amount of data from all over the world and carefully explored all possibilities.”
Room for smaller worlds
The result is a ceiling, not a closed door. Planets around the mass of Saturn or smaller could still orbit in the system’s habitable zones, where a rocky planet’s surface could hold liquid water.
“The study sets an upper limit, not a ban, on planets,” Li said. “Given how prevalent planets are in our universe and in the Milky Way, I would wager that we’ll find there are other planets there.”
That matters because binary systems are common. Roughly half of the star systems in the Milky Way contain at least two stars, so understanding where planets can and cannot form around them is central to estimating how many habitable worlds the galaxy holds.
“The new limit enables us to design optimum search strategies in the future,” Meyer said. The University of Michigan is part of a team studying a proposed mission called SHERA focused on binary systems, with 70 Oph AB among a handful of targets, and the system is expected to be a target for NASA’s planned Habitable Worlds Observatory.
The research team included scientists from more than a dozen institutions, including NASA’s Jet Propulsion Laboratory and IPAC at Caltech.
Notes
- Li, Y., et al. “A Century of Radial Velocity And Astrometric Monitoring of 70 Oph AB: New PFS Data and Constraints on Possible Planetary Companions.” The Astrophysical Journal, 29 September 2026. DOI: 10.3847/1538-4357/ae9f52.
- University of Michigan. “Suns set on hunt for giant planets in nearby binary system.” EurekAlert!, 29 September 2026. https://www.eurekalert.org/news-releases/1145703.
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