ron
September 15th 09, 04:41 PM
http://www.spaceflightnow.com/news/n0909/14saturn/
Lightning storm on Saturn breaks solar system record
EUROPEAN PLANETARY SCIENCE CONGRESS NEWS RELEASE
September 14, 2009
A powerful lightning storm in Saturn's atmosphere that began in
mid-January 2009 has become the Solar System's longest continuously
observed thunderstorm. It broke the record duration of 7.5 months set
by
another thunderstorm observed on Saturn by NASA's Cassini spacecraft
between November 2007 and July 2008.
The observations of the thunderstorm will be presented by Dr. Georg
Fischer of the Austrian Academy of Sciences at the European Planetary
Science Congress in Potsdam, Germany, on Tuesday 15 September.
The current thunderstorm on Saturn is the ninth that has been measured
since Cassini swung into orbit around Saturn in July 2004. Lightning
discharges in Saturn's atmosphere emit very powerful radio waves,
which
are measured by the antennas and receivers of the Cassini Radio and
Plasma Wave Science (RPWS) instrument. The radio waves are about
10,000
times stronger than their terrestrial counterparts and originate from
huge thunderstorms in Saturn's atmosphere with diameters around 3000
km.
Dr. Fischer said, "These lightning storms are not only astonishing for
their power and longevity, the radio waves that they emit are also
useful for studying Saturn's ionosphere, the charged layer that
surrounds the planet a few thousand kilometers above the cloud tops.
The
radio waves have to cross the ionosphere to get to Cassini and thereby
act as a natural tool to probe the structure of the layer and the
levels
of ionization in different regions."
The observations of Saturn lightning using the Cassini RPWS instrument
are being carried out by an international team of scientists from
Austria, the US and France. Results have confirmed previous studies of
the Voyager spacecraft indicating that levels of ionization are
approximately 100 times higher on the day-side than the night side of
Saturn's ionosphere.
Lightning storms on Saturn usually occur in a region that nicknamed
"Storm Alley" by scientists, which lies 35 degrees south of Saturn's
equator.
Dr. Fischer commented, "The reason why we see lightning in this
peculiar
location is not completely clear. It could be that this latitude is
one
of the few places in Saturn's atmosphere that allow large-scale
vertical
convection of water clouds, which is necessary for thunderstorms to
develop. However, it may be a seasonal effect. Voyager observed
lightning storms near the equator, so now that Saturn has passed its
equinox on 11 August, we may see the storms move back to equatorial
latitudes."
Saturn's role as the source of lightning was given added confirmation
during Cassini's last close flyby of Titan on August 25. During the
half
hour that Cassini's view of Saturn was obscured by Titan, no lightning
was observed.
"Although we know from Cassini images where Saturn lightning comes
from,
this unique event was another nice proof for their origin." said Dr.
Fischer.
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. NASA's Cassini
spacecraft has been in orbit around Saturn since July 2004. Cassini
completed its initial four-year mission to explore the Saturn System
in
June 2008. The Cassini Equinox mission is a two-year extension to
September 2010 and is named for the Saturnian equinox, which occurred
in
August 2009 when the sun shone directly on the equator. Cassini will
observe seasonal changes brought by the Sun as it begins to illuminate
the northern hemisphere and the rings' northern face. Saturn, the
rings
and moons were illuminated by the Sun from the south during the
mission's first four years
The Radio and Plasma Wave Science (RPWS) instrument receives and
measures the radio signals coming from Saturn, including the radio
waves
given off by the interaction of the solar wind with Saturn and Titan.
The Principle Investigator is Professor Donald Gurnett of the
University
of Iowa.
Lightning storm on Saturn breaks solar system record
EUROPEAN PLANETARY SCIENCE CONGRESS NEWS RELEASE
September 14, 2009
A powerful lightning storm in Saturn's atmosphere that began in
mid-January 2009 has become the Solar System's longest continuously
observed thunderstorm. It broke the record duration of 7.5 months set
by
another thunderstorm observed on Saturn by NASA's Cassini spacecraft
between November 2007 and July 2008.
The observations of the thunderstorm will be presented by Dr. Georg
Fischer of the Austrian Academy of Sciences at the European Planetary
Science Congress in Potsdam, Germany, on Tuesday 15 September.
The current thunderstorm on Saturn is the ninth that has been measured
since Cassini swung into orbit around Saturn in July 2004. Lightning
discharges in Saturn's atmosphere emit very powerful radio waves,
which
are measured by the antennas and receivers of the Cassini Radio and
Plasma Wave Science (RPWS) instrument. The radio waves are about
10,000
times stronger than their terrestrial counterparts and originate from
huge thunderstorms in Saturn's atmosphere with diameters around 3000
km.
Dr. Fischer said, "These lightning storms are not only astonishing for
their power and longevity, the radio waves that they emit are also
useful for studying Saturn's ionosphere, the charged layer that
surrounds the planet a few thousand kilometers above the cloud tops.
The
radio waves have to cross the ionosphere to get to Cassini and thereby
act as a natural tool to probe the structure of the layer and the
levels
of ionization in different regions."
The observations of Saturn lightning using the Cassini RPWS instrument
are being carried out by an international team of scientists from
Austria, the US and France. Results have confirmed previous studies of
the Voyager spacecraft indicating that levels of ionization are
approximately 100 times higher on the day-side than the night side of
Saturn's ionosphere.
Lightning storms on Saturn usually occur in a region that nicknamed
"Storm Alley" by scientists, which lies 35 degrees south of Saturn's
equator.
Dr. Fischer commented, "The reason why we see lightning in this
peculiar
location is not completely clear. It could be that this latitude is
one
of the few places in Saturn's atmosphere that allow large-scale
vertical
convection of water clouds, which is necessary for thunderstorms to
develop. However, it may be a seasonal effect. Voyager observed
lightning storms near the equator, so now that Saturn has passed its
equinox on 11 August, we may see the storms move back to equatorial
latitudes."
Saturn's role as the source of lightning was given added confirmation
during Cassini's last close flyby of Titan on August 25. During the
half
hour that Cassini's view of Saturn was obscured by Titan, no lightning
was observed.
"Although we know from Cassini images where Saturn lightning comes
from,
this unique event was another nice proof for their origin." said Dr.
Fischer.
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. NASA's Cassini
spacecraft has been in orbit around Saturn since July 2004. Cassini
completed its initial four-year mission to explore the Saturn System
in
June 2008. The Cassini Equinox mission is a two-year extension to
September 2010 and is named for the Saturnian equinox, which occurred
in
August 2009 when the sun shone directly on the equator. Cassini will
observe seasonal changes brought by the Sun as it begins to illuminate
the northern hemisphere and the rings' northern face. Saturn, the
rings
and moons were illuminated by the Sun from the south during the
mission's first four years
The Radio and Plasma Wave Science (RPWS) instrument receives and
measures the radio signals coming from Saturn, including the radio
waves
given off by the interaction of the solar wind with Saturn and Titan.
The Principle Investigator is Professor Donald Gurnett of the
University
of Iowa.