One rare sight with six exoplanets to orbit their central star in a uniquely syncopated orbital waltz scientists discovered. The research is published in the journal Nature.

The six planets orbit HD 110067, a bright star in the constellation Countess Berenices, about 100 light-years away, visible from Earth’s northern hemisphere. In 2020, NASA’s TESS space telescope, designed to search for exoplanets, detected dips in the star’s brightness, indicating that planets are passing in front of the star’s surface. With additional observations by the European Space Agency’s (ESA) CHEOPS space telescope, these signals were interpreted as transits of six planets in front of the star. These planets have a smaller radius than Neptune (which is why they are referred to as “sub-Neptunes”), which is common for exoplanets.

Studying the three innermost planets, the researchers calculated the orbits of all six planets, ranging from about nine days for the innermost planet to about 54 days for the outermost. All six planets are in coordinated orbits, meaning they exert a gravitational influence on each other as they orbit. Specifically, when the closest planet to the star makes three complete revolutions around it, the second one makes two at the same time. This is called a 3:2 coordination and is repeated between the four nearest planets. Among the most distant planets the pattern of four orbits for every three of the next planet was found (4:3 coordination).

The orbital arrangement of the planets shows that the system is largely unchanged since its formation more than a billion years ago. It is noted that planets around stars tend to form in coordination, but the balance can easily be disturbed, and multi-planet systems that maintain their coordination are rare.

“We think that only 1% of all systems remain in coordination,” says the study’s lead author, Raphael Luecke, from the University of Chicago. He adds that “this discovery is set to become a reference system for studying how sub-Neptunes, the most common type of planet outside our Solar System, form, evolve, and what they consist of and whether they have the right conditions to support the existence of water on their surface.”