Simulations of the 16 light-years-away binary star system 70 Ophiuchi indicate that Earth-sized planets can maintain stable orbits within the primary star’s habitable zone, even as researchers rule out giant planets behind an 1855 exoplanet claim.
Simulations Prove Stable Orbits Around 70 Ophiuchi AB
Located just about 16 light-years away in our stellar neighborhood, the system sits four times farther than our nearest neighbors in the Proxima Centauri system. An immense astronomy team from more than a dozen institutions focused their work on the binary system named 70 Ophiuchi (70 Oph AB). Its two stars are K dwarfs that measure approximately 88 percent and 73 percent the mass of the Sun. Calculations suggest the system is roughly 3 billion years old.
Planets with two suns might sound like science fiction from a galaxy far, far away, or even the 1895 work King in Yellow, but new research shows they can actually exist for a very long time.
These orange-y K dwarfs sit one rung down the stellar ladder from our Sun, making them smaller, dimmer, and cooler. They serve as prime targets in the search for habitability because they are calmer and less active than red dwarfs. They also boast potential lifespans of up to 70 billion years, making them seven times longer-lived than the Sun.
The system has been recognized as a binary for nearly 250 years, thanks to William Herschel. To understand its planetary potential, researchers incorporated recent and archival radial velocity measurements of both stars, pulling data from eight instruments for the primary star across a century of observation.
“Our solar system, with only one star, is actually somewhat unusual. Many stars have stellar companions.”
Stephen Kane, astrophysicist at the University of California, Riverside
Researchers achieved a radial velocity precision of better than 1 meter per second. To test what the data could reveal, scientists injected fake planet signals into their measurements. They also simulated Earth-mass planets at 2,000 different distances from the primary star, tracking each one over 10 million years.
“We calculated the boundaries of the habitable zone around the primary star. Then I tested whether an Earth-mass planet could maintain a stable orbit at different distances within that zone.”
Skylar D’Angiolillo, Earth and planetary sciences researcher at the University of California, Riverside
The team found that stable orbits remain possible within the habitable zone of the primary star. While a secondary star might seem like a wrecking ball capable of disrupting planetary survival, the simulations proved otherwise.
Squashing the 1855 Exoplanet Claim Behind 70 Ophiuchi
Scientists successfully ruled out the presence of Jupiter-mass or larger giant exoplanets around the two stars, extending their search out to about five astronomical units from the primary star. While terrestrial planets can survive in the system, the research closed the door on larger worlds.
That absence is notable because British astronomer William Jacob claimed in 1855 that 70 Oph AB possessed a planet, making it the first host of an exoplanet candidate. While Jacob’s original assertion did not survive scrutiny, subsequent measurements revealed a gravitational wobble that kept hopes alive for a hidden Jupiter-sized companion.
Instead of a giant planet, researchers determined that the supposed signal stemmed from stellar activity, a common hurdle for the radial velocity method.
“It’s a mix of disappointment and excitement,” says Yiting Li, an astronomer at U-M and the study’s first author. “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, astronomer at U-M and the study’s first author
Although giant worlds are absent, terrestrial planets remain below the current detection threshold. This leaves open the possibility that Earth-mass worlds exist within the system on stable paths.
Implications for Future Exoplanet Searches
Because more than half of all stars in the sky feature one or more stellar partners according to NASA, understanding binary habitability expands the scope of cosmic exploration. The framework developed in this study can be applied to other binary systems across the galaxy.
These efforts will gain momentum as next-generation technology comes online. Facilities such as NASA’s Habitable Worlds Observatory are specifically designed to explore and directly image alien worlds.
“Overall, our results demonstrate that it is possible for the 70 Oph system to host planets on S-type orbits around the primary star, including terrestrial planets on stable orbits within the habitable zone region. If stellar binaries can host Earth-like planets, 70 Oph is one of the best places to look.”
Research team, writing in The Astrophysical Journal
The system has been recognized as a binary for nearly 250 years.