Uranus and Four of Its Satellites

This infrared image of the planet Uranus was captured by the European Southern Observatory’s Very Large Telescope during the planet’s 2008 equinox. Every 42 years, the ring (and satellites) plane of Uranus line up with the Sun causing them to appear on edge from Earth’s point of view. A one minute exposure time was used, the maximum allowable to prevent the moving satellites from appearing as streaks. The IR filter used matches the absorption bands of the methane in the atmosphere of Uranus, making the relatively bright planet (almost) completely disappear. That permits the otherwise invisible rings and small satellites of Uranus to be detected instead of being lost in the glare of the planet. The bright spots on each side of Uranus are Miranda (~470 km diameter) and Ariel (~1100 km diameter). Two much smaller satellites can be seen just above the ring plane,to the left of the planet. Puck (~150 km diameter) is closer to the Planet than Portia (~100 km diameter).

Image Credit: ESO

The Rings of Uranus

Saturn’s rings are so prominent that they easily visible from Earth with a small telescope. All the other gas giant planets have ring as well, but they weren’t discovered until we were able to look at those planets from above the Earth’s atmosphere. Here are some pictures of the ring system around Uranus taken by the Hubble Space Telescope as our point of view shifted over several years. The next time the rings will be edge-on will be in 2049.

Image Credit: NASA / ESA / STScI


titania3_voyg2Titania’s tortured terrain is a mix of valleys and craters. Voyager 2 passed this moon of Uranus in 1986 and took this photograph. The long valleys indicate that Titania underwent some unknown tumultuous resurfacing event in its distant past. Titania is essentially a large dirty iceball composed of a roughly 50/50 mix of water ice and rock. It was discovered by William Hershel in 1787.

Image Credit: NASA

The Rings of Uranus

Uranus w ringsThese images from the Hubble Space Telescope show how the ring system around Uranus varies in appearance as viewed from Earth—culminating in the rings being seen edge-on. The edge-on rings appear as two spikes above and below the planet. The rings cannot be seen running fully across the face of the planet because the bright glare of the planet has been blocked out in the photo.  Shorter exposure color images of Uranus have been combined with the ring images to show the planet’s size and position relative to the ring plane.

From Earth, we can only see the rings’ edge every 42 years as the planet follows its 84-year orbit about the Sun. However, the last time the rings were tilted edge-on to Earth astronomers didn’t even know they existed. They were discovered in 1977.

Until Voyager 2 flew by Uranus in January, 1986, the rings were only known from the way they temporarily blocked the light of stars passing behind the planet. Hubble provided some of the first images of the ring system as viewed from Earth’s distance of approximately 2 billion miles. More recently, adaptive optics have allowed ground-based observers using large telescopes comparatively sharp views.

Two Views of Uranus

natural and false colorThese two pictures of Uranus—one in true color (left) and the other in false color—were compiled from images returned in 1986 from the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometers from the planet, several days from closest approach.

The picture on the left has been processed to show Uranus as human eyes would see it. It was assembled from images taken through blue, green, and orange filters. The darker shadings at the upper right of the disk correspond to the day-night boundary on the planet. The night side of the planet northern hemisphere of Uranus. (“Hold it,” I hear the Gentle Reader cry. “Shouldn’t the half of the northern hemisphere be in daylight.” No. Not on Uranus. The planet’s axis is tilted almost 90°.) The blue-green color results from the absorption of red light by methane gas in the planets deep, cold, and remarkably clear atmosphere.

The picture on the right uses false color and extreme contrast enhancement to bring out subtle details in the south polar region of Uranus. It uses images take through ultraviolet, violet, and orange filters shifted to the same blue, green, and red colors used to produce the picture at left. The very slight contrasts visible in true color are greatly exaggerated. The false color image reveals a dark polar hood surrounded by a series of progressively lighter concentric bands. One possible explanation is that smog, concentrated over the pole, is arranged into bands by zonal winds of the upper atmosphere. The bright orange and yellow strip at the edge of the planet’s limb is an artifact of the image enhancement.

Image Credit: NASA