Nearly 40 years after NASA launched Voyager 2 to explore interstellar space, astronomers have made a startling discovery hidden in decades-old data.

When Voyager 2 launched on August 20^th 1977, it made history as the first – and currently only – spacecraft to visit Uranus. On this historic mission, the spacecraft discovered 10 orbiting moons and two rings around the ice giant. One of the rings, dubbed Zeta, has been shrouded in mystery ever since – until now.

After its initial sighting, experts were unable to locate Zeta for almost 20 years. Experts even thought they’d “missed” Zeta because it was not visible in a single image.

Amateur image processor Ian Regan has shed new light on this illusive ring through rediscovered Voyager 2 data.

“He took hundreds of images, stacked them together, to produce this image of the Uranian system,” commented planetary scientist Matthew Hedman. “This is the most comprehensive view of the zeta ring that exists and we didn’t know it was in the Voyager data for decades.”

Thanks to this new information, researchers have been able to calculate Zeta’s distance from Uranus – around 37,000km – and to estimate its brightness.

“For a long time we thought we only had two images of this ring. This shows that there is a lot of information still encoded in the Voyager data that deserves a second look,” said Hedman.

This latest image of the Uranian system has raised some questions within the scientific community.

In 2007, Hawaii’s Keck Observatory gathered the first observations of Uranus’ rings since Voyager. Their findings showed Zeta 40,000km above Uranus, 20,000km further than Voyager 2 had imaged.

 “The trick is that the location of this ring didn’t match the Voyager images. Something has changed about this ring over the course of 20 years. We’re still not sure what it is,” Hedman explained.

Alongside this, experts in the Keck observatory detected that Zeta had become much brighter since its last sighting, meaning dust had been introduced into the system. One potential explanation could be a space rock colliding with Uranus, creating dust and debris that then settled in the zeta ring. Another theory holds changing seasons in space responsible, however these ideas are both unconfirmed.

“It got significantly brighter, which means dust got introduced to the system sometime in those 20 years,” Hedman said. “Now, what did that? We have no idea.”

As further questions are raised around the icy planet and its rings, experts are making plans to find answers. There’s even talk of a large-scale NASA mission on the horizon to explore the Uranus system.

For now, the James Webb Space Telescope is keeping an eye on Uranus, collecting further data and images of the planet’s rings. In September 2022, the clever space telescope captured some of the clearest images of Uranus’s rings we’ve ever seen – this is the first time we’ve seen the rings in infrared.

Sparked by Voyager’s historic mission into interstellar space, it seems we still have a lot to learn about the other planets in our solar system. As experts learn from this exciting discovery and plan future missions, we can’t wait to see what they’ll find next.