Researchers at the University of Michigan have ruled out Jupiter-sized planets in the inner regions of 70 Oph AB, a binary star system located 16 light-years from Earth. The finding resolves a 171-year mystery about a signal that could have indicated a giant planet's presence.
The team combined roughly a century of historical measurements with new observations from the Magellan Clay Telescope in Chile and the Harlan J. Smith Telescope in Texas. Their analysis determined that variations in stellar surface activity, rather than an orbiting planet's gravity, caused the mysterious wobble in the stars' radial velocity that astronomers had detected for decades.
"It's a mix of disappointment and excitement," said Yiting Li, a postdoctoral researcher at the University of Michigan. "We're finding out that there isn't a Jupiter-sized planet, but we're also opening the latest chapter on this historic system."
The research excluded planets with masses equal to or greater than Jupiter's within 5 astronomical units of 70 Oph A and within half an astronomical unit of 70 Oph B. An astronomical unit equals approximately 93 million miles.
The findings do not rule out smaller planets, including Saturn-sized worlds or rocky planets that could orbit within the system's habitable zone, where liquid water could exist on a planet's surface. Michael Meyer, a senior co-author and chair of the University of Michigan's astronomy department, noted that the results could guide future searches. "The new limit enables us to design optimum search strategies in the future," Meyer said. NASA's Habitable World Observatory is expected to target this system.
The study appears in The Astrophysical Journal and involved researchers from more than a dozen institutions, including NASA's Jet Propulsion Laboratory and IPAC at the California Institute of Technology.