40 years of Uranus's rings
This year marks the 40th anniversary of the detection of rings around Uranus. We speak to Jessica Mink, one of the scientists who made the discovery.
Words by Elizabeth Pearson
Uranus's rings imaged with the Hubble Space Telescope in 1997 in infrared and visible light
Image credit: Erich Karkoschka (University of Arizona), and NASA/ESA
On 10 March 1977, a group of researchers from Cornell University set off from Perth, Australia on board the Kuiper Airborne Observatory, hoping to image the occultation of the star SAO 158687 by Uranus. Jessica Mink was one of the researchers on the plane that day. She reveals how the team ended up discovering something far more interesting...
Our group’s research at the time was watching planetary occultations; stars getting blocked by planets. If you watch from the ground you often get clouded out and that’s really frustrating, so we turned to NASA's Kuiper Airborne Observatory to get us above the clouds.
There were three of us on the team. James Elliot was our principal investigator, and it was his idea. Edward Dunham was doing his PhD thesis project on planetary occultations and I had put together the data reduction system and would later analyse the data. Our plan was to study the atmosphere of Uranus during an occultation. We wanted to watch the star get blocked over time to get an idea of the temperature and pressure structure of the planet. You get a bunch of spikes as the atmosphere around the planet focuses and defocuses the star, and you look for spikes that are the same on either side of the planet. On 10 March the planet was due to occult a star and it turned out the best place to observe was over the Indian Ocean, so we flew from California, where the plane was based, to Perth, Australia.
On the day we did a long, 11-hour flight, turning around somewhere over the Kerguelen Islands. We went so far that we lost radio contact, and we later found out that our teram back on the ground, fearing the worst, had mobilised the the air rescue service!
We decided that since this we were on this long flight, we’d start well in advance to get a lot of time at Uranus; not something people always do. We were watching the readings on an analogue chart recorder, but before the main event we got a bunch of occultations we weren’t expecting.
Read more on the planet Uranus from BBC Sky at Night Magazine
The occultation of Uranus begins to appear on the readout chart. A version of the readout can be seen at the National Air and Space Museum in Washington, DC. Credit: Jessica Mink/Doug Mink
The planet occultation affected the star like we expected, but then after it came out from behind the planet, it got blocked again. We didn’t know for sure how close to symmetric the two blockages were, but it happened pretty much the same distance before and after. Once it was the same on the other side it was pretty clear this was being caused by the presence of rings, and that they were also blocking the star light.
When we got back to the hotel after the flight, James and Edward took the readout chart and ran it down the hallway, folding back on itself and found things matched up. We knew for sure what we had then. It was pretty exciting.
I’m having a hard time believing it’s been 40 years, but I like remembering it. It was fun.
The first direct images of the rings were taken in 1986, by the Voyager 2 spacecraft. Credit: NASA
The team initially found five rings though a further four were later found in the data. In 1986 Voyager 2 flew past the planet, sending back the first direct images of the rings, spotting another two. Two decades later, the Hubble Space Telescope discovered a pair of outer rings, bringing the total count to 13.