Cassini and Amateurs Chase Storm on Saturn

Feature April 29, 2010

Cassini and Amateurs Chase Storm on Saturn

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-143&cid=release_2010-143

With the help of amateur astronomers, the composite infrared spectrometer instrument
aboard NASA's Cassini spacecraft has taken its first look at a massive blizzard in
Saturn's atmosphere. The instrument collected the most detailed data to date of
temperatures and gas distribution in that planet's storms.

The data showed a large, turbulent storm, dredging up loads of material from the deep
atmosphere and covering an area at least five times larger than the biggest blizzard in this
year's Washington, D.C.-area storm front nicknamed "Snowmageddon."

"We were so excited to get a heads-up from the amateurs," said Gordon Bjoraker, a
composite infrared spectrometer team member based at NASA's Goddard Space Flight
Center in Greenbelt, Md. Normally, he said, "Data from the storm cell would have been
averaged out."

Cassini's radio and plasma wave instrument and imaging cameras have been tracking
thunder and lightning storms on Saturn for years in a band around Saturn's mid-latitudes
nicknamed "storm alley." But storms can come and go on a time scale of weeks, while
Cassini's imaging and spectrometer observations have to be locked in place months in
advance.

The radio and plasma wave instrument regularly picks up electrostatic discharges
associated with the storms, so team members have been sending periodic tips to amateur
astronomers, who can quickly go to their backyard telescopes and try to see the bright
convective storm clouds. Amateur astronomers including Anthony Wesley, Trevor Barry
and Christopher Go got one of those notices in February and were able to take dozens of
pictures over the next several weeks.

In late March, Wesley, an amateur astronomer from Australia who was actually the first
person to detect the new dark spot caused by an impact on Jupiter last summer, sent
Cassini scientists an e-mail with a picture of the storm.

"I wanted to be sure that images like these were being seen by the Cassini team just in
case this was something of interest to be imaged directly by Cassini or the Hubble Space
Telescope," Wesley wrote.

Cassini scientists eagerly pored through the images, including a picture of the storm at its
peak on March 13 by Go, who lives in the Philippines.

By a stroke of luck, the composite infrared spectrometer happened to be targeting the
latitude of the storms. The instrument's scientists knew there could be storms there, but
didn't know when they might be active.

Data obtained by the spectrometer on March 25 and 26 showed larger than expected
amounts of phosphine, a gas typically found in Saturn's deep atmosphere and an indicator
that powerful currents were dredging material upward into the upper troposphere. The
spectrometer data also showed another signature of the storm: the tropopause, the
dividing line between the serene stratosphere and the lower, churning troposphere, was
about 0.5 Kelvin (1 degree Fahrenheit) colder in the storm cell than in neighboring areas.

"A balloonist floating about 100 kilometers down from the bottom of Saturn's calm
stratosphere would experience an ammonia-ice blizzard with the intensity of
Snowmageddon," said Brigette Hesman, a composite infrared spectrometer team member
who is an assistant research scientist at the University of Maryland. "These blizzards
appear to be powered by violent storms deeper down – perhaps another 100 to 200
kilometers down – where lightning has been observed and the clouds are made of water
and ammonia."

The Cassini-Huygens mission is a cooperative 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 mission for NASA's Science Mission Directorate,
Washington, D.C. The Cassini orbiter and its two onboard cameras were designed,
developed and assembled at JPL. The composite infrared spectrometer team is based at
NASA's Goddard Space Flight Center, Greenbelt, Md., where the instrument was built.

#2010-142

-end-

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

Nancy Neal Jones/Elizabeth Zubritsky 301-286-0039/301-614-5438
Goddard Space Flight Center, Greenbelt, Md.
nancy.n.jones@nasa.gov/elizabeth.a.zubritsky@nasa.gov

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