You might imagine that second star coming through like a wrecking ball and making it impossible for an Earth-sized planet to survive in the habitable zone,
explains Stephen Kane, an astrophysicist at the University of California, Riverside, and co-author of a new study published in The Astrophysical Journal.
Researchers have modeled a binary star system located approximately 16 light-years away and determined that it could potentially support an Earth-sized planet in a stable, habitable-zone orbit where liquid water could remain stable on its surface, according to findings detailed by University of California, Riverside astronomers.
Simulating the 70 Ophiuchi System
The study centers on the binary system known as 70 Ophiuchi AB, or 70 Oph AB. Both stars within the system are slightly smaller and cooler than our Sun, possessing about 88% and 73% of its mass. Although astronomers have observed the system for decades and it has been recognized as a binary for nearly 250 years following observations by William Herschel, no confirmed planets currently orbit either star.
To investigate whether a terrestrial world could persist in such an environment, the research team incorporated archival and recent radial velocity (RV) measurements of both stars, gathering data from eight instruments across a century of observation. This approach achieved an RV precision of better than 1 meter per second.
Using these observational data, the researchers simulated Earth-mass planets at 2,000 different distances from the primary star, tracking each simulated world over a 10-million-year period. According to Skylar D’Angiolillo, an Earth and planetary sciences researcher at UCR and a study author, the team calculated the boundaries of the habitable zone around the primary star and tested whether a planet could maintain a stable orbit within it. The simulations demonstrated that stable orbits are indeed possible in that zone.
Tracing Exoplanet Limits in History
The system holds a notable place in astronomical history. In 1855, British astronomer William Jacob claimed that 70 Oph AB hosted a planet, which would have made it the first exoplanet candidate ever proposed. While that early claim did not survive later scrutiny, subsequent measurements revealed a gravitational wobble that kept the possibility of a Jupiter-sized companion alive.
However, the new analysis indicates that the observed signal stems from stellar activity rather than a giant gas planet. Yiting Li, an astronomer at the University of Michigan and the study’s first author, described the findings as a mix of disappointment and excitement,
noting that while the team ruled out Jupiter-mass or larger giant exoplanets out to about five astronomical units from the primary star, they are simultaneously opening the latest chapter on a historic system.
Although terrestrial planets currently remain below the detection threshold for direct observation, the modeling provides a framework indicating where Earth-mass planets are most likely to remain stable. Researchers suggest the methodology can also be applied to evaluate other binary star systems.
Evaluating Cosmic Habitability
Binary star systems with stellar companions are common throughout the universe, making single-star setups like our solar system relatively unusual. With more than half of all stars possessing stellar companions, understanding how planets interact with multiple gravitational fields matters for target selection.
While only a small fraction of confirmed exoplanets have been observed orbiting binary stars to date, studies like this help narrow down viable search targets before attempting direct imaging.
One reason this kind of work is important is that there are a lot of steps we can take before trying to directly observe a planet,
D’Angiolillo noted. We can ask first: Is this system even capable of hosting a potentially habitable planet?
