One of astronomy’s oldest suspected planetary systems has just undergone its most sensitive search yet and the biggest planets scientists might have expected to find are not there

Astronomers continue to revisit nearby star systems as increasingly accurate instruments make it possible to distinguish genuine planetary signals from other sources of stellar motion. A new investigation of 70 Ophiuchi AB has currently narrowed the possibilities for what may be orbiting this nearby binary system.

A Historic Planetary Mystery

Located around 16 light-years from Earth, 70 Ophiuchi AB consists of two K-type stars. Researchers led by the University of Michigan combined over a century of observations with modern high-precision measurements to search for proof of planets around either star.

The study, published in The Astrophysical Journal, found no statistically convincing proof for giant planets around the two stars.


The outcome does not establish that the system is planet-free. Instead, it positions stronger limits on large planets while leaving open the possibility of smaller worlds, that includes planets that could occupy possibly habitable orbits.

A Planet Claim Dating Back to 1855

70 Ophiuchi has been part of exoplanet history for over 170 years.

In 1855, British astronomer William Jacob reported irregularities in the motion of the stars and proposed that an unseen planetary companion might be responsible. That interpretation was later dismissed, but interest in potential planets around the system continued as improved observations found subtle changes in stellar velocity.

The binary is especially useful for long-term study as the two stars orbit one another around each 88 years. Its relatively close distance to Earth also makes it an attractive target for increasingly sensitive observations.

Almost half of Sun-like stars are found in binary or multiple systems, making questions regarding planet formation and survival around such stars important to know how common possibly habitable worlds might be.

Combining More Than a Century of Measurements

The research team brought together historical observations, modern radial-velocity measurements and astrometric details.

Radial velocity traces small changes in a star's movement toward or away from Earth. If a planet orbits the star, its gravitational influence can result in a detectable wobble in that motion.

The newest observations included information from the Planet Finder Spectrograph on the 6.5-meter Magellan Clay Telescope in Chile and measurements from McDonald Observatory in Texas. The researchers also made use of observations from earlier instruments, together with positional data from Hipparcos, Gaia and historical visual records.

The combined measurements enabled the researchers to reconstruct the binary system with high precision. They determined an orbital period of around 88.13 years and measured the stellar masses with uncertainties which is below 1%.

That precision was significant as the movement of the binary itself can obscure much smaller signals that might otherwise be attributed to planets.

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Stellar Activity Mimicked Planetary Signals

The researchers initially discovered recurring radial-velocity signals from 70 Ophiuchi A at periods close to 20 days, alongside shorter related durations.

Such a repeating pattern could potentially suggest an orbiting planet. However, further analysis showed that the signals corresponded closely with the star's around 20-day rotation period and its mathematical harmonics.

Computer models accounting for stellar activity offered a better explanation than models that included planets.

Features such as starspots and bright magnetic areas can alter the spectral lines used to find radial velocity. As these features move in a rotating star, they can create apparent shifts that resemble the gravitational impact of an orbiting planet.

What the Study Can Rule Out

The absence of a detected planet does not mean that no planets exist in the system. Instead, the observations suggest which types of planets would have been detectable if they were present.

The study strongly rules out Jupiter-sized companions across much of the inner areas of the system.

For 70 Ophiuchi A, Jupiter-mass planets within around 5 astronomical units can largely be excluded. Around 70 Ophiuchi B, the strongest current constraints reach almost half an astronomical unit.

The study's sensitivity varies with orbital distance. Around the primary star, planets more massive than approximately 0.3 Jupiter masses at 1 astronomical unit and almost 0.5 Jupiter masses at 2 astronomical units fall within its detection capabilities.

Smaller rocky planets are considerably more challenging to identify as their gravitational effects are much weaker. Their signals can become hidden beneath stellar activity that produces variability of many meters per second.

Smaller Worlds Remain Possible

Researchers used computer simulations to investigate whether planets could remain stable around either member of the binary system.

For 70 Ophiuchi A, simulations indicated that planetary orbits could remain stable across approximately the inner 2.5 to 2.9 astronomical units when suitably aligned with the binary's orbital plane. That area includes the star's modeled habitable zone.

A separate 2026 numerical study likewise concluded that both stars could maintain planets in permanently habitable areas under favorable orbital arrangements.

However, these calculations do not illustrate that habitable planets actually exist around 70 Ophiuchi. They suggest instead that the binary configuration does not automatically prevent planets from surviving in areas where potentially habitable conditions could happen.

Why the Null Result Matters

Finding nothing can be scientifically valuable when the search has been sensitive enough to exclude specific possibilities.

By removing massive planets from much of the likely architecture of 70 Ophiuchi, the study narrows the range of possibilities that future observations require to investigate. The system's proximity to Earth makes it a particularly interesting target for instruments made to search for smaller planets.

70 Ophiuchi is already being considered for future missions that could investigate planets via direct imaging or highly precise astrometry.

The Search Continues

Observations of other nearby binary systems have also illustrated the potential of modern instruments. In 2025, JWST detected evidence for a possible giant planet around Alpha Centauri A, featuring how newer technology can investigate planets in extremely nearby multiple-star systems.

For 70 Ophiuchi, the latest study offers a clearer picture of what has not been discovered while preserving the possibility of smaller planets.

After more than 170 years of speculation, the system's planetary mystery therefore continues to be open. The latest research has not concluded the search; instead, it has narrowed the focus toward smaller worlds that future instruments may be better equipped to find.

Source: BioScience and The Brighter Side of News