Enjoying EarthSky? Subscribe.

251,773 subscribers and counting ...

Today in science: Voyager 2 meets Uranus

In January 1986, Voyager 2 became the first and, so far, the only craft from Earth to see Uranus up close. It discovered a magnetic field and radiation belts, 2 new rings and 10 new moons.

Farewell, Uranus! Image acquired by Voyager 2 after sweeping past the planet, via NASA.

January 24, 1986. On this date, spacecraft Voyager 2 made its closest approach to the planet Uranus, passing 50,600 miles (81,500 km) from the planet’s cloudtops. It was the closest any earthly craft had ever come; in fact, even today, Voyager 2 remains Uranus’ only earthly visitor. As Voyager 2 passed Uranus, it sent back thousands of images and other scientific data, which let scientists make many discoveries about Uranus and its moons.

Voyager 2 was launched on August 20, 1977. The probe flew close to Jupiter in 1979 and Saturn in 1981. The trip to Uranus took much longer, nine years from its 1977 launch to the Uranus flyby. Voyager 2 sent us so much new information! For instance, the probe detected 10 new moons, for a total of 15 moons known at the time (today we know 27).

The largest of the 10 newly discovered moons was Puck, with a diameter of nearly 100 miles (150 km). It’s the largest of the minor moons of Uranus.

View larger. | Little Puck, largest of the small moons of Uranus, as seen by Voyager 2. Image via NASA.

Voyager 2 also took pictures of the moons we already knew about and revealed their amazing geology. For example, the last moon of Uranus to be discovered before the arrival of Voyager 2 was Miranda. Gerard Kuiper had discovered it from Earth as far back as 1948.

Thanks to Voyager 2, we saw Miranda much more clearly. In fact, it picked up the nickname of Frankenstein moon for its weird appearance.

Learn more about Uranus’ many moons.

Observe Miranda’s sharp and diverse features. Notice how it looks like an amalgamation of bits and pieces. Hence, Frankenstein moon! Image by Voyager 2 via NASA/JPL-Caltech.

It had been discovered from Earth that Uranus – like Saturn – has rings. Voyager 2 surveyed Uranus’ rings and discovered 2 new ones, bringing the total number of rings to 11. Today, there are 13 known rings.

Read more about the rings of Uranus

Voyager 2 acquired this image of Uranus’ rings on January 21, 1986, at a distance of 2.5 million miles (4.1 million km). Image via NASA.

Rings in solid colour and orbits of moons in dotted lines. Image by Ruslik0 via Wikimedia Commons.

Voyager 2 also discovered the presence of a magnetic field around Uranus. This discovery led scientists to believe that the planet’s crazy seasons are not the worse consequence of the planet’s unique tilt. Due to the planet’s tilt, the magnetic field is also tilted at 59 degrees from the axis of rotation. In other words, the rotational and magnetic poles are so far apart that a compass would be useless. This creates a very non-uniform magnetic field that can vary by up to 10 times!

The probe also discovered that Uranus has radiation belts similar to those of Saturn in intensity. Earth also has radiation belts with the two main ones being known as the Van Allen belts.

Read more about Uranus’ magnetosphere

The pale blue atmosphere of Uranus is due to the presence of methane. Voyager 2 image via NASA.

And Voyager 2 studied the composition of the atmosphere of Uranus. It discovered that its atmosphere is very similar to that of the other gas giants and is composed mainly of hydrogen and helium. The interior of the planet contains more volatile gases such as methane, ammonia and water. In fact, methane is responsible for the planet’s green-blue colour since it absorbs light of longer wavelengths (red).

And so Voyager 2 vastly increased our knowledge of Uranus … and then left this world behind.

By the way, Uranus was discovered by accident by William Herschel in 1781. It’s 19.8 AU (astronomical units) away from the sun on average. Uranus is also sometimes called ‘the sideways planet’ because of its large tilt of 98 degrees. This means that the planet’s equator is almost perpendicular to its orbit! Astronomers are still trying to explain what caused this crazy tilt with many different theories. Since “the axial tilt is the reason for the season”, Uranus has perhaps the most interesting seasonal pattern of the solar system.

Read more about Uranus from NASA

Bottom line: Voyager 2 swept closest to Uranus on January 24, 1986.

Daniela Breitman