During a break from looking at planets around other stars, the European Space Agency’s CHaracterising ExOPlanet Satellite (Cheops) mission has observed a dwarf planet in our own Solar System and made a decisive contribution to the discovery of a dense ring of material around it.

The dwarf planet is known as Quaoar. The presence of a ring at a distance of almost seven and a half times the radius of Quaoar, opens up a mystery for astronomers to solve: why has this material not coalesced into a small moon?

One of the most interesting stars in the Milky Way is still serving up more than its fair share of intrigue.

In October 2020, SGR 1935+2154, the magnetar responsible for spitting out radio signals never before detected in our home galaxy, unexpectedly slowed down.

Now, scientists believe the rotational slowdown could be evidence of a volcano-like eruption on its surface, spewing material out into space that altered the star’s environment enough to decelerate the spinning of the planet minutely.

“When we put everything together, we saw drops in brightness that were not caused by Quaoar, but that pointed to the presence of material in a circular orbit around it,” said Bruno Morgado of the Universidade Federal do Rio de Janeiro in a statement. “The moment we saw that we said, ‘Okay, we are seeing a ring around Quaoar.’”

Quaoar is part of a collection of about 3,000 dwarf planets known as trans-Neptunian objects, which are beyond the orbit of the planet Neptune.

Scientists are now wondering why the dense material in Quaoar’s ring has not come together to form a small moon, because the ring itself is “at a distance of almost seven and a half times the radius of Quaoar,” the ESA said.