Saturn Does The Wave
In Upper Atmosphere
(7 May 2008) Two decades of
scrutinising Saturn are finally paying off, as scientists have discovered a
wave pattern, or oscillation, in Saturn's atmosphere only visible from Earth
every 15 years.
The discovery of the wave pattern is the result
of a 22-year campaign observing Saturn from Earth (the longest study of
temperature outside Earth ever recorded), and the Cassini spacecraft's
observations of temperature changes in the giant planet's atmosphere over
time.
The Cassini infrared results, which appear in the same issue of
Nature as the data from the 22-year ground-based observing campaign, indicate
that Saturn's wave pattern is similar to a pattern found in Earth's upper
atmosphere. The earthly oscillation takes about two years. A similar pattern on
Jupiter takes more than four Earth years. The new Saturn findings add a common
link to the three planets.
Just as scientists have been studying climate
changes in Earth's atmosphere for long periods of time, NASA scientists have
been studying changes in Saturn's atmosphere. Glenn Orton of NASA's Jet
Propulsion Laboratory in Pasadena, Calif., says patience is the key to studying
changes over the course of a Saturnian year, the equivalent of about 30 Earth
years.
"You could only make this discovery by observing Saturn over a
long period of time," said Orton, lead author of the ground-based study. "It's
like putting together 22 years worth of puzzle pieces, collected by a hugely
rewarding collaboration of students and scientists from around the world on
various telescopes."
The wave pattern is called an atmospheric
oscillation. It ripples back and forth within Saturn's upper atmosphere. In
this region, temperatures switch from one altitude to the next in a candy
cane-like, striped, hot-cold pattern. These varying temperatures force the wind
in the region to keep changing direction from east to west, jumping back and
forth. As a result, the entire region oscillates like a wave.
A
"snapshot" of the hot-cold temperature patterns in Saturn's atmosphere was
captured by the Cassini Composite Infrared Spectrometer. Along with Earth-based
data, the "snapshot" also uncovered other interesting phenomena. Among them:
the temperature at Saturn's equator switches from hot to cold, and temperatures
on either side of the equator switch from cold to hot every Saturn
half-year.
Mike Flasar, co-author of the Cassini paper, and principal
investigator for Cassini's Composite Infrared Spectrometer at NASA's Goddard
Space Flight Center, Greenbelt, Md., said that Cassini helped define this
oscillation in combination with the ground observation campaign.
"It's
this great synergy of using ground-based data over time, and then getting up
close and personal with the oscillation in Saturn's atmosphere through
Cassini," said Flasar. "Without Cassini, we might never have seen the structure
of the oscillation in detail."
Cassini scientists hope to find out why
this phenomenon on Saturn changes with the seasons, and why the temperature
switchover happens when the sun is directly over Saturn's equator.
The
Cassini-Huygens mission is a co-operative project of NASA, the European Space
Agency and the Italian Space Agency. JPL, a division of the California
Institute of Technology in Pasadena, manages the Cassini mission for NASA's
Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed,
developed and assembled at JPL. The Composite Infrared Spectrometer team is
based at NASA's Goddard Space Flight Center, Greenbelt, Md.
(source:
Diya Chacko, NASA Jet Propulsion Laboratory)
