III.

Observation from Earth and Space

Because Uranus is so far from Earth (2,840 million km/1,760 million mi), only one spacecraft has visited the planet. During a rare alignment of the four giant planets, the spacecraft Voyager 2, which was launched on August 20, 1977, was able to pass by Jupiter (in 1979), Saturn (in 1981), Uranus (in 1986), and Neptune (in 1989). Scientists launched Voyager 2 with just enough energy to pass Jupiter. However, the strong gravitational pull of Jupiter accelerated the spacecraft as it passed by the planet so that Voyager 2 had enough energy to reach Saturn. As Voyager 2 successively passed each of the four giant planets, the gravitational pull of each planet accelerated the spacecraft enough to help it reach the next planet.

As Voyager 2 passed by Uranus, the spacecraft recorded and transmitted images of the planet, its rings, and some of its moons. Astronomers studying these images discovered five previously undetected rings and ten previously undiscovered moons. In addition to discovering these inner moons, Voyager 2 passed close to Miranda, the 11th satellite from Uranus, and mapped the moon’s surface in detail. Surface features of Miranda include craters, canyons, and geologically young systems of ridges and grooves. Because the other large satellites were more distant from the spacecraft’s path, Voyager 2 was unable to make detailed images of their surfaces.

The Hubble Space Telescope has also observed Uranus in different wavelengths, including infrared radiation. Discoveries include two additional moons and two additional rings, and changes in the planet’s atmosphere.