Astronomers have ruled out Jupiter-sized planets in the inner regions of 70 Ophiuchi AB, a binary star system located 16 light-years from Earth. The discovery resolves a 171-year mystery about a mysterious stellar wobble that could have signaled a giant planet.
Researchers from the University of Michigan, NASA's Jet Propulsion Laboratory, and other institutions combined roughly a century of historical measurements with new observations from the Magellan Clay Telescope and the Harlan J. Smith Telescope. They found that variations in stellar surface activity, not gravitational influence from a planet, caused the observed wobble in the stars' radial velocity.
The analysis ruled out 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 is approximately 93 million miles.
While giant planets are now excluded from these regions, smaller worlds could still orbit either star. Planets the size of Saturn or smaller, including rocky worlds within the system's habitable zone, remain undiscovered. The habitable zone is the region around a star where temperatures could allow liquid water on a planet's surface.
"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."
Michael Meyer, chair of the University of Michigan's astronomy department, noted that the findings could guide future searches. "The University of Michigan is part of a team studying a space mission called SHERA that will focus on binaries, where this system is one of a handful of targets. 70 Oph AB will certainly be a target of flagship missions, such as NASA's Habitable World Observatory."
The research was published in The Astrophysical Journal.