On January 24, 1986, a 721.9kg (1,592lb) hunk of machinery called Voyager 2 skimmed as close as we've ever got to the planet Uranus and gave us our first, and (so far) only, deep look at one of the Solar System's oddest planets.
Uranus is the first world to be discovered using a telescope, and given its 2.9-billion-mile distance from the Sun, there was very little known about the ice giant. After a nine-year trip from Earth, the Voyager 2 space probe flew within 81,500km (50,600 miles) of the planet, and gave us the first close-up look at Uranus' ring system. In doing so, we discovered 10 new moons around the world.
"The Uranus encounter was very exciting for me," said Suzanne Dodd, project manager for Voyager, based at NASA's Jet Propulsion Laboratory.
"It was my first planetary encounter and it was of a planet humanity had never seen up close before. Every new image showed more details of Uranus, and it had lots of surprises for the scientists. I hope another spacecraft will be sent to explore Uranus, to explore the planet in more detail, in my lifetime."
The pictures showed off the planet's unique orientation: it orbits the Sun on its side, a pole pointing towards our star while the other pole is left in shadow for half of its 84-year orbit.
It has been speculated that a massive impact rolled the planet onto its side. Other theories include a now-disappeared massive moon that dragged the planet onto its side, or that Uranus was just born that way.
It had been known since 1977 that there were rings around Uranus – not on a par with Saturn's magnificent setup but discernible nevertheless. The Voyager 2 images showed that in addition to had what been spotted from Earth, two huge dark rings encircled Uranus.
When the probe flew by, it beamed back proof that the planet had a magnetic field somewhat similar to our own, although the magnetic and physical north-south poles didn't match.
"We got to Uranus and saw that the poles were closer to the equator," said Ed Stone, project scientist for the Voyager mission. "Neptune turned out to be similar. The magnetic field was not quite centered with the center of the planet."
As the probe got closer to Uranus it also detected a cluster of 10 previously unseen moons circling the blue planet. Before that discovery, we knew Uranus had five natural satellites, and so Voyager 2 took this total to 15. Some 43 have now been discovered circling Uranus.
Voyager 2 has carried on through space after peering at the mysterious Uranus. It'll be at least another 15 years before we get to probe the world's icy depths again. Earth-bound telescopes are still examining the planet, and there may be bigger surprises in the depths of Uranus yet to come. ®