Star system found with six Neptune-size planets orbiting in perfect mathematical harmony

Astronomers have identified a star system, named HD 110067, where six planets keep steady orbital ratios with one another. This pattern is a resonance, which means each world completes a set number of laps while its neighbor finishes a different, simple count.

A clear example is “three orbits of the inner planet for every two orbits of its neighbor.” When a chain like this persists for billions of years, it signals the star system has had a quiet history without major disruptions.

That stability turns HD 110067 into a useful record of how planets formed and settled. It also gives researchers a reliable framework for measuring sizes, masses, and atmospheres with precision.

HD 110067 is relatively nearby

The star at the center of this six-planet system, HD 110067, sits about 105 light-years away in the constellation Coma Berenices. It is a K-type star, which means it is smaller and cooler than the Sun.

Its steady light lets observers measure the tiny dip during a transit, when a planet passes in front of the star, and the subtle wobble known as the radial-velocity signal, which reveals the gravitational pull of orbiting planets.

Those two methods together pin down how large each planet is and how much it weighs. With that, scientists can derive densities and begin to infer what the planets are made of and what kind of air they might carry.

Finding this six-planet system

NASA’s TESS spacecraft first recorded repeating, shallow dips in the starlight that matched transiting planets.

The timing of the first few signals hinted that resonance might be shaping the architecture, which allowed researchers to forecast when other transits should appear.

ESA’s CHEOPS satellite then observed the star during those predicted windows and saw the expected crossings.

Those detections helped rule out misleading “alias” periods that can arise when overlapping signals blur together.

With the pattern established, analysts reexamined older TESS data and uncovered faint, previously missed transits right where the rhythm predicted. Ground-based telescopes then secured additional, well-timed events.

Resonant orbit ratios of HD 110067

The six planets, labeled b through g from the inside outward, align in a chain of simple steps: three consecutive 3:2 ratios among the inner neighbors, followed by two 4:3 ratios among the outer pairs.

Put another way, for every six orbits of the innermost planet, the outermost completes about one.

Long, intact chains like this are uncommon because gravitational nudges or past collisions often disrupt resonances over time.

The clean sequence in HD 110067 offers a clear view of orbital dynamics in a stable configuration rather than in a system shaped by later upheaval.

Sizes, orbits, and temperatures

All six worlds fall into the “sub-Neptune” category: larger than Earth but smaller than Neptune. Their sizes range from roughly two to almost three times Earth’s radius.

They circle the star quickly, with orbital periods from about 9 days for the innermost planet to roughly 55 days for the outermost.

At those distances, they receive strong starlight and heat. The innermost planet reaches temperatures of several hundred degrees Celsius, and even the outer planets remain too warm for Earth-like conditions.

These are not habitable environments, but they offer clear targets for studying planetary composition and air.

Masses and densities

Transits give sizes directly, but masses require tracking the star’s motion over time and separating true planetary tugs from stellar activity. Starspots and other variability produce “noise” that can mask or mimic planetary signals.

By using high-precision spectrographs and accounting for the star’s 20-day rotation signal, researchers measured masses for several planets and set strong limits for the rest.

Combining those masses with the measured radii yields densities that are too low for purely rocky bodies.

The results point to hydrogen-rich envelopes – mini-Neptunes rather than super-Earths – with puffy atmospheres that expand the planets’ apparent sizes.

Atmospheres in HD 110067

This configuration is well suited for transmission spectroscopy, which reads starlight that filters through a planet’s air during a transit.

Certain wavelengths are absorbed by molecules such as water vapor or methane, leaving fingerprints in the spectrum. By comparing spectra taken during and outside a transit, instruments can identify those molecules.

Because HD 110067 hosts several similar-sized planets under the same starlight, scientists can assemble a comparative “family portrait” of sub-Neptune atmospheres.

That kind of dataset addresses key questions about why sub-Neptunes are common among discovered planets and how their atmospheres change under different levels of irradiation.

Resonance and history

Planets grow within a young star’s disk of gas and dust. During that phase, they can migrate inward or outward because of interactions with the surrounding material.

Neighboring planets often get captured into resonances as their paths adjust. After the gas disperses, later gravitational encounters, lingering debris, or impacts can break those patterns.

The intact 3:2–3:2–3:2–4:3–4:3 chain in HD 110067 implies the planets avoided major disturbances after formation.

The orderly layout records a path in which slow migration shaped the system early, and the subsequent environment remained calm enough to preserve the timing.

Almost perfect in many ways

The star’s reliable light allows precise measurements of transit times, and small variations in those times refine the orbits further.

The planets’ radii mostly sit above the “radius valley,” a gap that separates smaller, likely rocky super-Earths from larger, gas-rich sub-Neptunes.

Their orbital planes appear closely aligned, which explains why so many of them transit from our viewpoint.

That alignment also leaves room for more distant planets on wider orbits that we have not yet seen. If any additional worlds share the same alignment, their transits could become visible in future monitoring.

To sum it all up, HD 110067 is a stable, resonant system of warm sub-Neptunes that offers a clear laboratory for comparing planetary atmospheres under the same star, and for testing how gentle migration in young disks can set long-lasting orbital patterns.

Together, these near-perfect features make the system a prime target for future studies.

The full study was published in the journal Nature.

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