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NASA Science News
NASA's Hubble Space Telescope has
captured dramatic images of two swirling storms on Jupiter
as they collided to form a truly titanic tempest.
October 24, 2000
-- For the first time, scientists have been able to watch
two of Jupiter's giant storms, each about half the size
of Earth, colliding and merging to form an even bigger tempest.
A similar merger centuries ago may have created Jupiter's
famous Great Red Spot, a storm that is twice as wide as
our planet and at least 300 years old.
"Usually
when we've seen two of [the white ovals] approaching each
other, they bounce back [apart]," said Glenn Orton,
senior research scientist at NASA's Jet Propulsion Laboratory.
But this time the storms came together in a complicated
dance that scientists recorded using the Hubble Space Telescope
and ground-based observatories.
For sixty long years Jupiter's striking
white ovals, pictured here in an image from NASA's Galileo
spacecraft, existed as distinct storms. Since 1998 they've
merged to form a titanic tempest second in size only to
the Great Red Spot itself. Recent observations from the
Hubble Space telescope captured for the first time two of
the ovals in the act of coalescing.
Seeing
the collision of two such storms will help scientists understand
more about the dynamics of Jupiter's atmosphere, says Agustin
Sanchez-Lavega, an astronomer at Universidad del Pais Vasco,
who reported the team's observations yesterday at a meeting
of the American Astronomical Society in Pasadena. One question
has been how deeply the roots of a storm at Jupiter's cloud
tops extend into lower layers. In this year's merger, the
upper layer seemed to move differently than underlying clouds.
Three
white oval storms, in a band of Jupiter's atmosphere farther
south than the Great Red Spot, became active about 60 years
ago. In the following decades until 1998, they sometimes
approached each other but never collided. In early 1998,
two of the ovals were approaching each other as Jupiter
went out of sight from Earth, behind the Sun. When the planet
came back into view, the two had become one.
"We
weren't able to see how they came together that time,"
Orton said.
Last
year, the oval resulting from the 1998 combination approached
the remaining one of the original three ovals. Each was
a swirling high-pressure vortex, upwelling at the center
and spinning winds counterclockwise to about 470 kilometers
per hour. One was about 9,000 kilometers across, the other
slightly smaller.
These four Hubble Space Telescope images show steps in
the consolidation of three "white oval" storms
into one over a three-year span of time.
A third,
darker oval, swirling clockwise instead of counterclockwise,
formed temporarily between the two white ovals. That type
of interceding system may be what usually keeps white ovals
from colliding, the team proposed. But in this case, the
middle storm appears to have been pushed even farther south
and torn apart as all three passed near the Great Red Spot
last December.
The
disappearance of the opposite-swirling storm cleared the
way for the two white ovals to meet.
Their
collision dance began in March and lasted about three weeks.
At the cloud tops, the storms circled around each other
counterclockwise, then consolidated into a single oval about
one-third wider than either had been beforehand. The ovals'
approach and merger was viewed in various wavelengths, showing
events at different depths, with a planetary telescope at
Pic-du-Midi in France, NASA's Infrared Telescope Facility
in Hawaii, and the orbiting Hubble Space Telescope, a facility
of NASA and the European Space Agency.
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