During the past decade, many bright spots have been seen on Uranus, in both red and near-infrared filters. But this is the first dark spot ever seen on the planet. A team led by Lawrence Sromovsky of the University of Wisconsin and including Kathy Rages of the SETI Institute, Heidi Hammel of the Space Science Institute (Boulder, CO), and Patrick Fry of U. Wisconsin, observed the dark spot on Aug. 23 using the Hubble Space Telescope (HST).

Other images taken a day later also show the dark spot near Uranus’ limb, a sure sign that the spot had a lifetime of at least several days. In fact, we can be sure the spot had a lifetime of at least two months. A team led by Mark Showalter of the SETI Institute also has been observing Uranus with Hubble in an effort to understand the planet’s rings and satellites. Some of their images taken on June 16 show the dark spot, two months prior to its discovery.

The recent observations also showed a bright spot just to the north of the dark spot, which may have some people scratching their heads and asking “Why do I think I’ve seen that before?” They probably remember the Voyager images of Neptune’s Great Dark Spot and its associated Bright Companion. It would be very exciting to see similar features forming on Uranus as spring comes to the northern hemisphere after decades of winter darkness. Uranus’ bright spot, however, is located at 30°N latitude, an area where bright spots have been seen on many previous occasions. In enlarged images of this region the bright spot doesn’t appear to be connected to the dark one, and is probably just a case of two spots passing by each other. Read More

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