ESA’s Cheops Mission Discovers Rare Ring Around Dwarf Planet

Credit: European Space Agency

The European Space Agency’s (ESA) Cheops (Characterizing ExOPlanet Satellite) mission has made an unexpected discovery during its exoplanetary exploration. While observing the dwarf planet Quaoar, a ring was discovered orbiting around it. Located in the Kuiper Belt, Quaoar is the third known small solar system body with a ring confirmed around it. The ring is not visible through a telescope but was discovered through a series of eclipses caused when Quaoar passed in front of four stars. This process is known as stellar occultation. 

This ring is remarkable because it is estimated to be 2,500 miles away from Quaoar, much farther out than the Roche limit, which is estimated at 1,100 miles for Quaoar. The Roche limit is the maximum distance material orbiting a parent body would be pulled apart by the tidal forces exerted by the parent body. What this means for Quaoar is that any material further away than 1,100 miles would coalesce into a moon; a ring should theoretically only exist within that 1,100-mile radius. In other words, this ring should not be there. This raises questions about how this ring has survived and has scientists reconsidering what they know about the Roche limit. 

The Cheops mission was launched in late 2019 and is expected to last through mid-2023. The mission’s primary goal is to gather information on the thousands of planets detected over the past few decades. These exoplanets orbit bright stars, which is what the space telescope on CHEOPS observes. With parts on board, VPT is proud to be part of this historic program and congratulates everyone involved with its success, including this groundbreaking discovery.