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Cassini confirms a dynamic atmosphere at Saturn's moon Enceladus

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-Partical Physics and Astronomy Research Coucil (PPARC)
-Jet Propulsion Laboratory, California Institute of Technology
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Imperial College London and PPARC news release

For immediate release
Friday 29 July 2005

The latest close flyby of Saturn's icy moon Enceladus by NASA's Cassini spacecraft confirms that the moon has a significant, extended and dynamic atmosphere. The flyby, which took place on 14th July 2005, was Cassini's lowest altitude flyby of any object to date, a mere 173 kilometres (108 miles) above the surface of Enceladus.

The 500 km diameter moon Enceladus is a very bright icy moon at a distance of 4 Saturn radii away from Saturn. It has long been associated with the formation of the E ring, Saturn's outermost ring. The first two more distant flybys of Enceladus on February 17th at an altitude of 1,167 kilometres (725 miles), and on March 9th, 500 kilometres (310 miles) above Enceladus' surface had shown draping or bending of the magnetic field around the moon, revealing that Enceladus was acting as a large obstacle to the flow of plasma and magnetic field from Saturn by its extended asymmetric atmosphere.


The recent close flyby confirms and extends the observations from the two more distant flybys which took place earlier this year. Although no other instruments on the Cassini spacecraft had detected evidence of this atmosphere on the first two flybys, on the basis of the magnetometer [MAG] instrument observations alone a decision was made to modify the spacecraft trajectory for the 14th July encounter to fly much closer to the surface of Enceladus.

Professor Michele Dougherty from Imperial College London, who is Principal Investigator on the Magnetometer instrument on Cassini, says "These latest observations are very exciting, they confirm the existence of an atmosphere which we predicted from the distant earlier flybys and they will also allow us to gain a much better understanding of the processes taking place which are producing this very exotic atmosphere".

Observations from numerous instruments now confirm what MAG was able to see from a great distance. Not only is the magnetic field even more strongly bent around the atmospheric obstacle connected to the moon but the other instruments also detected the presence of the atmosphere. The magnetic data also suggests that the atmosphere is not symmetric and may be arising from a comet-like jet from the southern hemisphere. Also the spacecraft passed right through the electric current carrying region associated with the atmospheric interaction.


For further information, please contact:

Abigail Smith, Imperial College London Press Office
Tel: +44 20 7594 6701. Mobile: 0780 886248.

Gill Ormrod, PPARC Press Office
Tel +44 1793 442012. Mobile: 0781 8013509.

Professor Michele Dougherty - Principal Investigator, Magnetometer Imperial College London
Tel: +44 20 7594 7757. Mobile: +44 7990 973761.

Carolina Martinez - Jet Propulsion Laboratory, Pasadena, Califonia, USA
Tel: +1 (818) 354-9382.

Professor Fritz Neubauer - Co-investigator, Magnetometer University of Koln
Tel: + 0049 221 02310 or 0049 2235 92274
Email: neubauer@geo.Uni-Koeln.DE

Carolina Martinez - Jet Propulsion Laboratory, Pasadena, California, USA
Tel: +1 (818) 354-9382.

Notes to Editors

1. Saturn's rings
The rings are (in order out from the planet) D, C, B, Cassini Gap, A, F, G and E. The A ring has its own gap called the Encke Gap.

2. Previous PPARC release on previous two flybys -

3. For an artist's impression of the third flyby of Enceladus see

For images, including those from the three flybys of Enceladus, and information on the Cassini mission visit and

4. The Cassini-Huygens 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The magnetometer team is based at Imperial College London, working with team members from the United States and Germany.

5. Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (11,000) and staff (6,000) of the highest international quality.
Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture.

6. The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Particle Physics Laboratory, CERN, the European Space Agency and the European Southern Observatory. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.