Steady Star System

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.

- Author: Eric Ralls, Earth.com