Huge
Spring Storms Rouse Uranus from Winter Hibernation
If springtime on Earth
were anything like it will be on Uranus, we would be
experiencing waves of massive storms, each one
covering the country from Kansas to New York, with
temperatures of 300 degrees below zero.
A dramatic new
time-lapse movie by NASA's Hubble Space Telescope
shows for the first time seasonal changes on the
planet. Once considered one of the blander-looking
planets, Uranus is now revealed as a dynamic world
with the brightest clouds in the outer Solar System
and a fragile ring system that wobbles like an
unbalanced wagon wheel. The clouds are probably made
of crystals of methane, which condense as warm bubbles
of gas well up from deep in the atmosphere of Uranus.
The movie, created by
Hubble researcher Erich Karkoschka of the University
of Arizona, clearly shows for the first time the
wobble in the ring system, which is made of billions
of tiny pebbles. This wobble may be caused by Uranus'
shape, which is like a slightly flattened globe, along
with the gravitational tug from its many moons.
Although Uranus has
been observed for more than 200 years, "no one
has ever seen this view in the modern era of astronomy
because of the long year of Uranus -- more than 84
Earth years," said Dr. Heidi Hammel,
Massachusetts Institute of Technology.
The seasonal changes on
Earth are caused by our planet's rotational pole being
slightly tilted. Consequently, the Earth's Southern
and Northern hemispheres are alternately tipped toward
or away from the Sun as the Earth moves around its
orbit. Uranus is tilted completely over on its side,
giving rise to extreme 20-year-long seasons and
unusual weather. For nearly a quarter of the Uranian
year, the sun shines directly over each pole, leaving
the other half of the planet plunged into a long,
dark, frigid winter.
The Northern Hemisphere
of Uranus is just now coming out of the grip of its
decades-long winter. As the sunlight reaches some
latitudes, it warms the atmosphere. This appears to be
causing the atmosphere to come out of a frigid
hibernation and stir back to life. Uranus does not
have a solid surface, but is instead a ball of mostly
hydrogen and helium. Absorption of red light by
methane in the atmosphere gives the planet its cyan
color.
Uranus was discovered
March 13, 1781, by William Herschel. Early visual
observers reported Jupiter-like cloud belts on the
planet, but when NASA's Voyager 2 flew by in 1986,
Uranus appeared as featureless as a cue ball. In the
past 13 years, the planet has moved far enough along
its orbit for the sun to shine at mid-latitudes in the
Northern Hemisphere. By the year 2007, the sun will be
shining directly over Uranus' equator.
Karkoschka, Hammel and
other investigators used Hubble from 1994 through 1998
to take images of Uranus in both visible and
near-infrared light.
CONTACT:
Donald Savage
Headquarters, Washington, DC
(Phone: 202/358-1727)
Nancy Neal
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-0039)
Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)
The Space
Telescope Science Institute is operated by the Association
of Universities for Research in Astronomy, Inc. (AURA),
for NASA,
under contract with the Goddard
Space Flight Center, Greenbelt, MD. The Hubble
Space Telescope is a project of international
cooperation between NASA and the
European Space Agency (ESA).
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