Astronomers spot rare star system with six planets in geomet…

Astronomers have discovered a rare star system in which six planets orbit around a star in an elaborate geometric pattern due to a phenomenon called orbital resonance. Using both NASA’s Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency (ESA)’s Exoplanet Satellite (CHEOPS), researchers have created a picture of the beautiful, but complex HD110067 system, located 100 light years away.

The system’s six planets orbit in a pattern whereby one planet completes three orbits while another completes two, another completes six orbits while another completes one, and another completes four orbits while another completes three, and so on. The six planets form what is called a “resonance chain”, where each planet is in resonance with the planets next to it.

A rare family of six exoplanets has been unlocked with the help of ESA's Cheops mission.  All the planets in this family are smaller than Neptune and move in a very precise waltz around their star HD110067.  When the planet closest to the star makes three complete revolutions around it, the other one makes exactly two revolutions during the same time.  This is called 3:2 resonance.  The six planets form a resonant chain in pairs of 3:2, 3:2, 3:2, 4:3, and 4:3, resulting in the nearest planet completing six orbits while the outermost planet completes one orbit.  Cheops confirmed the orbital period of the third planet in the system, which was the key to unlocking the rhythms of the entire system.  This is the second planetary system in orbital resonance that Cheops has helped reveal.  The first one is called TOI-178.
A rare family of six exoplanets has been unlocked with the help of the European Space Agency’s CHEOPS mission. ESA, CC BY-SA 3.0 IGO

It is this series of resonances that makes the system so unusual. “Among the more than 5,000 exoplanets discovered orbiting stars other than our Sun, resonances are not rare, nor are systems with multiple planets rare. However, it is extremely rare to find systems where the resonance extends over such a long range of six planets,” one of the researchers, Hugh Osborn of the University of Bern, explained in a statement.

All of the planets in this system are of a type called sub-Neptunians, which are planets smaller than Neptune that are unlike any other planet in our solar system, but they are considered some of the most common exoplanets. Planets are thought to often form in resonance due to gravitational forces, however, this delicate balance is easily disturbed by a disturbance such as the impact of a passing star or a large asteroid or comet.

The orbital geometry of HD110067: tracing a link between two neighboring planets along their orbits at regular time intervals produces a pattern unique to each pair.  The six planets of the HD110067 system together form a mesmerizing geometric pattern due to their resonance series.
Detecting a link between two neighboring planets at regular time intervals along their orbits produces a unique pattern for each pair. The six planets of the HD110067 system together form a mesmerizing geometric pattern due to their resonance series. CC BY-NC-SA 4.0, Death Roger/NCCR Planets

Researchers are keen to investigate systems like HD110067 because it can show what a system might look like if it did not experience any of these dramatic events.

“We believe that only about 1% of all systems remain in resonance,” said University of Chicago researcher Rafael Luque. “It shows us the ancient configuration of a planetary system that has remained untouched.”

This research has been presented in Nature Journal.






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