Quirks & Quarks·Analysis

Scientists say a return to Uranus should be a highest priority

Bob McDonald's blog: In 1986 Voyager flew by the distant giant planet, but we haven't been back since, and now a U.S. advisory panel says its time to give Uranus a close look.

Bob McDonald's blog: We haven't visited the strange and mysterious giant since 1986

This is an image of the planet Uranus taken by the spacecraft Voyager 2. NASA's Voyager 2 spacecraft flew closely past distant Uranus, the seventh planet from the Sun, in January 1986. ( NASA/JPL)

Thirty-six years ago, the Voyager 2 robotic spacecraft made humanity's one and only visit to distant planet Uranus. Now a scientific panel is urging a return to the strangest planet in our solar system.

In January of 1986, I celebrated my birthday at the Jet Propulsion Laboratory in Pasadena California, joining an international group of journalists and scientists to watch the first ever closeup images of Uranus come down from space.

It was the latest episode in the remarkable Voyager mission which began with the launches of the twin Voyager spacecraft in 1977. We'd already seen them fly past Jupiter and Saturn, but both of those planets had been visited by spacecraft before. 

Uranus, however, was entirely new territory, and a completely different world.

NASA's Voyager 2 flew past Uranus in 1986, coming within 81,500 km of the planet on it's closest approach on January 24. (NASA)

The most striking feature of the seventh planet from the sun is its sideways orientation. Most planets in the solar system spin in more or less the same plane — like a fleet of rotating tops spinning around the sun.

Uranus, however, seems like it's been knocked on its side. Its rotation is tilted by 98 degrees relative to the plane of the sun and planets. By comparison, Earth's tilt is only about 23 degrees.

Among other things, it means that unlike on Earth, the sun doesn't rise and set during the 17 hours Uranus takes to spin around its axis. In fact, from the Uranian perspective, during its 84 Earth-year journey around the sun, the sun will rise at its north pole, and set at the south pole only once. 

Voyager found a strong magnetic field on Uranus, but it's unlike those of the other planets of our solar system. It's skewed at an odd angle, radically different from the axis of spin. Adding to the oddity, the magnetic field is not centred on the core of the planet, but off to one side. There is definitely something strange going on inside this sideways world.

And in 1986, as the first closeup colour pictures arrived, we were all amazed at how featureless Uranus was: a smooth sphere tinted blue by methane in its upper atmosphere. The exact details of what lies below that smooth face is still a mystery to this day. Uranus is colder than Jupiter and Saturn and made of a combination of rock, ices and gas. Since it's about four times larger than the Earth, it's sometimes referred to as an ice giant.

The Hubble space telescope took this image in of Uranus in 1998. The rings have been brightened for visibility. (NASA/JPL/STSci)

However, while the planet itself may look somewhat featureless, the rings and moons surrounding it are another story.

Tenuous rings are different from both the brilliant white icy rings of Saturn, or the gossamer thin dusty ring of Jupiter. Uranus is surrounded by nine charcoal-dark rings forming thin circular lines with four brighter dusty rings outside them, though brighter is a relative term. In fact they're very difficult to detect in visible wavelengths of light, and most of what we know of them is from their faint infrared glow. 

Along with the rings is a family of 27 moons, most of them made of ice and quite small.

One of them, Miranda, has such a bizarre looking surface, some scientists have suggested it could have been shattered by a collision with a large object in the past, then the pieces all came back together again jumbled up. 

Now, in a report released this week, the advisory body that recommends priorities for U.S. planetary exploration, the National Academies of Sciences, Engineering, and Medicine, has put a mission to Uranus at the top of the list, identifying it as "one of the most intriguing bodies in the solar system," whose peculiarities "all present major puzzles."

Flying by in early 1986, Voyager 2 captured this picture of Uranus's moon Miranda. Scientists have speculated that its scarred and shattered surface could be a result of the body being broken apart and then reassembled. (NASA)

They've endorsed a plan for a spacecraft called the Uranus Orbiter and Probe that would fly to Uranus and circle the planet for several years, possibly dropping a probe into the atmosphere. This would reveal details about the interior structure, along with close-ups of the planet's rings and moons.

But it might also indirectly provide insights into planets orbiting other stars.

Many exoplanets that have been found around stars in our galaxy are in the size range of Uranus, which is an intermediate size, smaller than giant Jupiter but larger than our rocky Earth.

So while Uranus may be the oddball in our solar system, planets like it may be the norm elsewhere in the galaxy, which makes it worth exploring.


Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.