A mysterious star system just 16 light-years away may be hiding habitable planets
Astronomers have solved a 170-year-old planetary mystery in a nearby two-star system, discovering that a mysterious wobble was caused by stellar activity rather than a giant planet. Although Jupiter-sized worlds have been ruled out in key regions, smaller, potentially habitable planets could still be waiting to be discovered just 16 light-years from Earth.
Key points
- Researchers found no Jupiter-sized or larger planets in examined regions of 70 Ophiuchi AB, 16 light-years away.
- The mysterious wobble is likely caused by stellar surface activity, not a giant planet.
- Smaller planets, including rocky worlds in the habitable zone, could still exist and are targets for future missions.
A star system 16 light-years from Earth has puzzled astronomers for more than 170 years. New research led by the University of Michigan has ruled out the presence of Jupiter-sized or larger planets in specific regions of 70 Ophiuchi AB, a binary star system where two stars orbit each other. The study, supported in part by NASA and published in The Astrophysical Journal, used an exceptionally sensitive analysis to search for massive planets.
The finding resolves a long-standing mystery: a signal that once suggested a giant planet hiding there is now attributed to variations in the stars' surface activity. While the result rules out certain massive planets, it also narrows the search for smaller worlds that could potentially support life.
What the study found
The team combined roughly a century of historical measurements with new observations from the 6.5-meter Magellan Clay Telescope in Chile and the 2.7-meter Harlan J. Smith Telescope in Texas. Their analysis was sensitive enough to distinguish an apparent planetary signal from changes on the stars themselves. They concluded that stellar activity, not a giant planet's gravity, caused the wobble in radial velocity measurements.
Specifically, no planets with masses equal to or greater than Jupiter's were found within 5 astronomical units of 70 Oph A and within half an astronomical unit of 70 Oph B. An astronomical unit is about 93 million miles. The study also precisely determined the orbits of the two stars.
It's a mix of disappointment and excitement. We're finding out that there isn't a Jupiter-sized planet, but we're also opening the latest chapter on this historic system.
— Yiting Li
Implications for future searches
The results leave open the possibility that smaller planets, such as Saturn-sized or rocky worlds, orbit either star. Some could reside in the system's habitable zone, where temperatures might allow liquid water on a planet's surface under suitable atmospheric conditions. Knowing which planets are absent can help design more efficient future searches.
Michael Meyer, a senior co-author and chair of the University of Michigan's astronomy department, said the new limit enables optimum search strategies. He noted that 70 Oph AB will be a target for NASA's Habitable World Observatory and the proposed SHERA mission. Yiting Li, a postdoctoral researcher, said the study sets an upper limit, not a ban, on planets and that other planets are likely to be found there.
