A century of monitoring 70 Ophiuchi AB rules out giant planets, but habitable Saturns remain possible

Star system: 70 Ophiuchi A | Distance from the Sun: 16.7 light years

The 70 Ophiuchi AB binary system, just 5.1 parsecs from Earth, is a prime target for future searches for Earth-like planets. Astronomers combined new radial velocity data from the Planet Finder Spectrograph with decades of previous measurements and astrometry to refine the orbits and masses of both stars. The study found no evidence for giant planets around either star, but set strong limits on what kinds of planets could still be hiding there.

For 70 Ophiuchi A, the data rule out Jupiter-mass planets within 5 astronomical units, and are sensitive enough to detect planets as small as 0.3 Jupiter masses at 1 au. For 70 Ophiuchi B, planets more massive than about 0.25–0.3 Jupiter masses are excluded inside 0.5 au. The analysis shows that stable orbits for planets around 70 Ophiuchi A extend out to about 2.5 au, covering the star’s habitable zone. This means that Saturn-mass or smaller planets could still exist in stable, potentially habitable orbits. The results provide important guidance for future planet searches in this nearby system.

Key findings
- No giant planets detected around 70 Ophiuchi A or B after a century of monitoring
- Jupiter-mass planets are ruled out within 5 au of 70 Ophiuchi A
- Planets more massive than 0.25–0.3 Jupiter masses are excluded inside 0.5 au of 70 Ophiuchi B
- Stable, potentially habitable orbits exist for Saturn-mass or smaller planets around 70 Ophiuchi A
- The system remains a top target for future searches for Earth-like planets

Scientific study

A Century of Radial Velocity and Astrometric Monitoring of 70 Oph AB: New PFS Data and Constraints on Planetary Companions (external link)