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: 'Eye of Sauron': Using supermassive black holes to measure cosmic distances

add to favorites email to friend print save as pdf

Related Stories

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 ...

James Cook and the transit of Venus

Jun 04, 2012

Every ~120 years a dark spot glides across the Sun. Small, inky-black, almost perfectly circular, it's no ordinary sunspot. Not everyone can see it, but some who do get the strangest feeling, of standing, to ...

STAR TRAK for February 2012

Feb 02, 2012

As evening twilight fades during February, the two brightest planets, Venus and Jupiter, will highlight the sky as they come into view in the southwest.

Recommended for you

A colorful gathering of middle-aged stars

20 hours ago

NGC 3532 is a bright open cluster located some 1300 light-years away in the constellation of Carina(The Keel of the ship Argo). It is informally known as the Wishing Well Cluster, as it resembles scattered ...

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.