Modeling the 70 Ophiuchi Binary System
Researchers at the University of California, Riverside have modeled a nearby binary star system and determined that it could potentially support an Earth-sized planet in a stable orbit where liquid water might exist. The binary star system, known as 70 Ophiuchi or 70 Oph AB, is located about 16 light-years away, or approximately 5 parsecs in cosmic terms.
The concept of worlds orbiting more than one star has long captured public imagination in works of fiction. In reality, the two stars in the 70 Ophiuchi 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, no confirmed planets currently orbit either star.
Simulations and Habitable Zone Calculations
To better understand how the two stars move around each other, the research team incorporated recent and archival radial velocity measurements of both stars, drawing on data from eight instruments for the primary star across a century of observation. The radial velocity method measures tiny changes in a star’s velocity resulting from the gravitational pull of another body, achieving a precision of better than 1 meter per second.
Researchers simulated Earth-mass planets at 2,000 different distances from the primary star, tracking each simulation over a period of 10 million years. Skylar D’Angiolillo, an Earth and planetary sciences doctoral student at UC Riverside who conducted the dynamical modeling, explained the methodology according to Sciencealert: 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.
The habitable zone refers to the region around a star where a planet is warm enough to maintain liquid water on its surface. Stephen Kane, an astrophysicist at UC Riverside and co-author of the study, addressed misconceptions about binary systems as reported by UC Riverside: 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. But these simulations show that isn’t necessarily the case.
Historical Context and Future Outlook
The system has a lengthy history in astronomical observation. It has been recognized as a binary system for nearly 250 years, initially noted by William Herschel. British astronomer William Jacob made a claim in 1855 that 70 Oph AB hosted a planet, though that early claim did not hold up to scrutiny. More recent measurements detected a stellar wobble that could have indicated a Jupiter-sized planet, but researchers determined that signal stemmed from stellar activity rather than a giant planet.
While terrestrial planets in the system remain below current detection thresholds, the dynamical modeling provides a framework that can be applied to other binary systems as well. Researchers suggest that an Earth-sized planet could potentially be discovered in the habitable zone even before the launch of the Habitable Worlds Observatory.
