Hubble Discovers a Dark Cloud in the Atmosphere of Uranus

Sep 28, 2006
Hubble Discovers a Dark Cloud in the Atmosphere of Uranus
Credit: NASA, ESA, L. Sromovsky and P. Fry (University of Wisconsin), H. Hammel (Space Science Institute), and K. Rages (SETI Institute)

Just as we near the end of the hurricane season in the Atlantic Ocean, winds whirl and clouds churn 2 billion miles away in the atmosphere of Uranus, forming a dark vortex large enough to engulf two-thirds of the United States.

Lawrence Sromovsky of the University of Wisconsin-Madison leads a team that used NASA's Hubble Space Telescope to take the first definitive images of a dark spot on Uranus. The elongated feature measures 1,100 miles by 1,900 miles (1,700 kilometers by 3,000 kilometers).

There have been prior unconfirmed sightings of dark spots on Uranus, including sketches made in the early 1900s, low-contrast ultraviolet Voyager spacecraft flyby images in 1986, and near-infrared observations taken from a ground-based observatory in 1993. However, no other Hubble images taken almost every summer from 1994 through early 2006 have shown such a dark spot. This indicates that the current dark disturbance probably formed very recently, researchers said.

Although rare on Uranus, dark spots have been frequently observed on Neptune. Uranus is similar in size and atmospheric composition to Neptune, but it has not appeared to have as active an atmosphere. Recently, however, Uranus's atmosphere has shown an increase in activity.

The development of a dark spot may be a signal of the oncoming uranian northern spring, said researchers. Uranus is approaching its December 2007 equinox, when the Sun will shine directly over the equator. "We have hypothesized that Uranus might become more Neptune-like as it approached its equinox," said team member Heidi B. Hammel of the Space Science Institute in Boulder, Colo. "The sudden appearance of this unusual dark feature suggests we might be right."

The dark spot was detected at a latitude of 27 degrees in Uranus's northern hemisphere, which is just now becoming fully exposed to sunlight after many years of being in shadow. Astronomers are keenly interested in how strongly and quickly the atmosphere of Uranus seems to be responding to seasonal sunlight changes.

Uranus's rotation axis is tilted almost parallel to its orbital plane, such that the planet appears to be rotating on its side. This sideways orientation leads to extreme seasons during the planet's 84-year path around the Sun.

This three-wavelength composite image was taken with Hubble's Advanced Camera for Surveys on August 23, 2006. The research team found the dark spot again on August 24. The inset image shows a magnified view of the spot with enhanced contrast. Uranus's north pole is near the 3 o'clock position in this image. The bright band in the southern hemisphere is at 45 degrees south.

Source: Space Telescope Science Institute

Explore further: The riddle of galactic thin–thick disk solved

Related Stories

Planets can alter each other's climates over eons

Feb 20, 2015

A new study sheds light on how exoplanets in tightly-packed solar systems interact with each other gravitationally by affecting one another's climates and their abilities to support alien life.

Some of the best pictures of the planets in our solar system

Jan 19, 2015

Our Solar System is a pretty picturesque place. Between the Sun, the Moon, and the Inner and Outer Solar System, there is no shortage of wondrous things to behold. But arguably, it is the eight planets that make up our Solar ...

Clues revealed about hidden interior of Uranus

Nov 14, 2014

(Phys.org) —Long believed to be one of the blandest regions of any of the giant gas planets, the southern hemisphere of Uranus indicates a flurry of previously unknown atmospheric phenomena, hinting at ...

Recommended for you

The riddle of galactic thin–thick disk solved

18 hours ago

A long-standing puzzle regarding the nature of disk galaxies has finally been solved by a team of astronomers led by Ivan Minchev from the Leibniz Institute for Astrophysics Potsdam (AIP), using state-of-the-art ...

Giant cosmic tsunami wakes up comatose galaxies

20 hours ago

Galaxies are often found in clusters, with many 'red and dead' neighbours that stopped forming stars in the distant past. Now an international team of astronomers, led by Andra Stroe of Leiden Observatory ...

Astronomers find runaway galaxies

Apr 23, 2015

We know of about two dozen runaway stars, and have even found one runaway star cluster escaping its galaxy forever. Now, astronomers have spotted 11 runaway galaxies that have been flung out of their homes ...

Celestial fireworks celebrate Hubble's 25th anniversary

Apr 23, 2015

The glittering tapestry of young stars flaring to life in this new NASA/ESA Hubble Space Telescope image aptly resembles an exploding shell in a fireworks display. This vibrant image of the star cluster Westerlund ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.