Feature
Volunteers Help NASA Track Return of the Dragon
02.13.06
Image to right: This is a 3-frame animated gif movie taken by amateurs Erick Bondoux and Jean-Luc Dauvergne using a 12 inch diameter telescope in Melun, France (about 35 mi south of Paris). These images were taken on evening of January 25, 2006. South is up which is theusual view in an Earth-based telescope. The white spot seen moving from right to left is associated with the storm system detected by the Cassini Radio and Plasma Wave Science instrument. The storm suddenly appeared on January 23 and still continues as of February 13, 2006. Size of white spot is approximately size of continental U.S."Right now, Cassini is in a 40-day orbit around Saturn, and we are slowly flying over the night side, so it's difficult to see cloud features," said Dr. Michael Kaiser of NASA's Goddard Space Flight Center, Greenbelt, Md. "We know the storm is there because radio signals from lightning flashes are being detected by Cassini's Radio and Plasma Wave Science (RPWS) instrument, in the same way that thunderstorms on Earth generate static on AM radio." Kaiser is part of a team using RPWS to observe the storm.
According to the RPWS data, the new storm is generating lightning flashes several times more frequently than the original Dragon storm, and the lightning is as much as five times stronger. At approximately the size of the continental U.S., the storm dwarfs terrestrial thunderstorms. Apparently, it is much fiercer as well -- radio signals from its lightning are more than 1,000 times greater than similar radio static from terrestrial storms.
Kaiser added, "I know of an organization of dedicated amateurs (and some professionals) called the Association of Lunar and Planetary Observers. I contacted their director and asked him to query his troops to see if anyone saw any new bright clouds in Saturn's atmosphere. I heard back very quickly from Erick Bondoux and Jean-Luc Dauvergne of Melun, France, two amateurs who worked together, and then later from two separate U.S. amateurs (Jim Phillips of Charleston, S.C., and Don Parker of Coral Gables, Fla.). All groups saw a new white patch of high clouds where the storm should be. Amateurs are playing an increasingly important role supporting professional astronomy research. The equipment available now is incredible, much better than when I was an amateur," said Kaiser.
"The storm is still ongoing, with 35 consecutive episodes as of February 8," said Kaiser. "It waxes and wanes in intensity -- strongest during episode 2, weakest during episode 10 so far." Kaiser noticed signals from the storm on January 23. Each episode lasted about half a Saturn day of 10 hours and 40 minutes when the storm system is on the side of Saturn facing Cassini. (Some episodes may have been longer, but were not detectable by Cassini when the storm is on Saturn's day side.)
According to the team, the white spot is the tip of the iceberg for the storm, like the cumulus clouds on top of thunderstorms on Earth. Visual lightning flashes in the cloud tops will be hard to observe because the actual location of the lightning is likely much deeper in Saturn's atmosphere, where it is warm enough for water vapor to exist. On Earth, turbulent motion of water droplets and ice particles in clouds separates electric charge, resulting in lightning. Something needs to separate electric charge on Saturn for lightning to occur there also, and water in deeper layers of the atmosphere is a likely candidate.
The storm appears in Saturn's "storm alley," a band located at about 30 to 35 degrees south latitude. The area is between two jets of winds moving at different speeds. This wind shear generates tremendous turbulence in storm alley, which may be part of the reason why storms emerge so frequently there, according to the team. "However, why the storms suddenly emerge and disappear is a mystery," said Kaiser. "Storms on Saturn seem to be exquisitely sensitive to the turbulent atmosphere there, just like a tornado that suddenly appears beneath the roiling clouds of a thunderstorm, and just as suddenly is gone. We don't know why yet."
The ultimate source of energy for the storms may be heat from Saturn's interior. Saturn formed from a cloud of gas and dust that collapsed under its own gravity. This collapse, and condensation processes in the deep interior, generated tremendous heat. Today, 4.5 billion years after its formation, Saturn still radiates about the same amount of heat energy that it receives from the Sun.
As Cassini gets closer to Saturn, the team would like to pinpoint the location of the lightning. "Our RPWS instrument can locate a radio signal to within a one to two degree angle, but we are so far from Saturn now that this small angle includes the entire planet. Once we get closer, Saturn will appear much larger to Cassini, and we can better locate the lightning if the storm is still ongoing," said Kaiser.
The RPWS team includes Principal Investigator, Prof. Donald Gurnett and colleagues Drs. Bill Kurth and Georg Fischer, from the University of Iowa, Drs. Alain Lecacheux, Philippe Zarka, and Baptiste Cecconi from the Observatory of Paris, France, and Drs. Mike Kaiser and Bill Farrell from Goddard. The Cassini mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Science Mission Directorate, Washington.
NASA Goddard Space Flight Center
Phone: (301) 286 0039 / 5017