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.
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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