Voyager 2 captured this stunning parting shot of Uranus as it headed off towards its next destination, Neptune. (Image: NASA/JPL-Caltech)

After re-examining data acquired by the Voyager 2 spacecraft, astronomers have detected wavy patterns in two of Uranusā€™s dark system of ringsā€”patterns that may be indicative of two undiscovered moons.

Like the other gas giants in our solar system, Uranus features a ring system, though itā€™s not nearly as spectacular as the one around Saturn. And like the other gas giants, Uranus hosts a batch of natural satellitesā€”27 to be exact. New research suggests this number might have to be revised; data collected by Voyager 2 during its historic 1986 flyby hints at two undiscovered moons lurking around a pair of Uranusā€™ rings.


The suspected new moons reside in Alpha and Betaā€”the 5th and 6th rings. (Image: Public domain)

Uranus is almost 20 times farther from the sun than the Earth, making direct observations difficult. Voyager 2 found 10 moons when it visited the planet in 1986, tripling the number of moons known to orbit the gas giant. But it appears the probeā€™s satellite-hunting days arenā€™t over just yet. Planetary scientists Rob Chancia and Matthew Hedman from the University of Idaho recently revisited Voyager 2's old data, and they noticed something peculiar in two of Uranusā€™ 13 rings, Alpha and Beta.

The two rings exhibit a series of wavy patterns consistent with the presence of two tiny moons. ā€œThese patterns may be wakes from small moonlets orbiting exterior to these rings,ā€ write the researchers in their study.

Importantly, these observations are consistent with how Uranusā€™ other moons, such as Cordelia and Ophelia, are exerting gravitational pressure on the dust, rocks, and ice within the rings, herding the particles along a narrow formation.


If these moons exist, theyā€™re quite dark and very tiny, measuring a mere two to nine miles (four to 14 km) across. That would make them smaller than any other known moon to orbit the planet, which explains why Voyager 2 wasnā€™t able to detect them directly.

Armed with this possibility, the researchers are planning to inspect Uranus with the Hubble Space Telescope. Failing that, we could always send a new space probe. Itā€™s been three decades since our last visit to Uranus, after all.


[arXiv via New Scientist]