Several of Uranus’ moons may someday collide

Tiny moon Cressida is also causing distortion in one of the planet’s rings.

Scientists studying the unusual shape of one of ice giant Uranus’ thin rings determined that at least two of the planet’s moons will someday collide with one another.

When a research team led by Robert Chancia of the University of Idaho learned that Uranus’ Eta ring has a somewhat triangular rather than completely circular shape, they set out to identify the cause of the unusual feature.

That cause turned out to be Cressida, a tiny moon just 51 miles (82 km) in diameter, which is gravitationally interacting with several of its fellow Uranian  moons.

Once the scientists determined Cressida’s exact shape and size, they were able to successfully measure its density and mass, which they then used to confirm a future collision, likely with neighboring moon Desdemona, in several million years.

The two moons are separated by just 560 miles (900 km).

Upon discovering that the speed of the strange ring distortion, which orbits Uranus much faster than individual ring particles, matches Cressida’s orbital speed, the researchers recognized Cressida as the cause of the anomaly.

Uranus has 27 known moons, two of which, Belinda and Cupid, were shown in 2012 to be on a collision course with one another sometime in 10 to 1,000 million years.

The study that discovered this was conducted by SETI Institute scientists Robert French and Mark Showalter.

Two of Uranus’ thin, diffuse rings are believed to be the products of earlier collisions between moons subsequently destroyed in the impact(s).

A collision between Cressida and Desdemona could result in a similar, new ring around the planet, or could create “new” moons, which scientists have nicknamed “Cupbel” and “Cresdemona.”

Cressida has a mass approximately 1/300,000th that of Earth’s Moon. With a density 86 percent that of water, Cressida is likely composed of rock and water ice.

A paper on the findings will be published in the Astronomical Journal.