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Enceladus continues to intrigue scientists


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For immediate use
Tuesday 30 August 2005

Further results from the Cassini spacecraft's July flyby of Enceladus reveal more detail about the features and processes of Saturn's moon. Speaking at a press conference at Imperial College London this morning, the Cassini scientists spoke about the intriguing south pole area which has a surprising hotspot and 'tiger stripe' features on the surface.

Following the two distance flybys of Enceladus in February and March this year results from the Magnetometer instrument showed a flowing of the magnetic and plasma field from Saturn towards and then around Enceladus. Effectively Enceladus was acting as an obstacle to the flow - indicating the presence of an atmosphere. In addition there was an indication of an internal signature.

Professor Michele Dougherty Opens in new window, from Imperial's Department of Physics and the lead scientist for the Magnetometer instrument, explained:

Enceladus

"On the basis of the results obtained from the Magnetometer instrument from the two first flybys we persuaded the Cassini team to take a much closer look at Enceladus. As a result on 14th July we were able to get within 173 km of the surface enabling all of the instrument teams to get data which is starting to build up a really surprising picture of the processes at work on this moon. We were able to confirm the presence of an atmosphere following the third flyby. Whilst it was found around the whole body is was concentrated at the south pole indicated by the presence of a cloud of water vapour."

Images from the Imaging Science Subsystem (ISS) team on Cassini revealed Enceladus in incredible detail - with the south pole region being of particular interest because of its relatively smooth terrain indicating that it is relatively young. The long, cracked features dubbed 'tiger stripes' are very young - between 10 and 1,000 years.

These findings support previous results that the moon's southern pole is currently active and has undergone episodes of geologic activity as recently as 10 years ago. These cracks, which are approximately 80 miles long are roughly parallel to one another and are spaced about 25 miles apart. The cracks act like vents. They spew out vapour and fine ice water particles that have become ice crystals. The crystals can be dated, which helped scientists pin down the age of the features.

Press conference

Cassini's visual and infrared mapping spectrometer shows water ice exists in two forms on Enceladus: pristine, crystalline ice and radiation-damaged amorphous ice. When ice comes out of the hot cracks at the south pole - the 'tiger stripes' - it forms as fresh crystalline ice. As the ice near the pole remains cold and undisturbed it ages and coverts to amorphous ice. Since this process is believed to take place over decades or less, the 'tiger stripes' must be very young.

"One of the most fascinating aspects of Enceladus is that it's so very small as icy moons go, but so very geophysically active. It's hard for a body as small as Enceladus to hold onto the heat necessary to drive such large-scale geophysical phenomena, but it had done just that," said Dr Bob Brown, team leader for the visual and infrared mapping spectrometer from the University of Arizona. "Enceladus and its incredible geology is a marvellous puzzle for us to figure out."

Torrence Johnson from the Jet Propulsion Laboratory is a member of the ISS team. He said: "Enceladus has certainly thrown up more surprises than anticipated - which is great for planetary science. We are piecing together the results from the various instrument teams to build up more of a complete picture of what is happening on Enceladus. With more data analysis and further flybys planned for later in the year we are beginning to understand more about this icy satellite."

Enceladus and its south pole - the story so far:

  • the presence of an exotic atmosphere - concentrated at the south pole
  • large crevasse features at the south pole dubbed 'tiger stripes'
  • an intriguing hot spot at the south pole - particular in the area of the tiger stripes - showing similarities to features seen at Jupiter's moon, Io. Temperatures warmer than expected.
  • presence of 'orderly' water ice at the south pole, especially within the tiger stripe features, indicating that it must have been very hot, be very young or both.
  • presence of simple organics along the fractures
  • indication that water vapour and fine material are originating from the 'hot' polar cap region. The production of water vapour and ejection of fine material are connected as they are in a comet - suggesting that these materials are coming from the tiger stripes.

For further information contact:

Gill Ormrod, PPARC Press Office
Tel +44 1793 442012. Mobile: 0781 8013509.
Email: gill.ormrod@pparc.ac.uk

Laura Gallagher - Imperial Press Office
Tel: 020 7594 6702. Mobile : 07803 886248
Email : l.gallagher@imperial.ac.uk

Professor Michele Dougherty - Principal Investigator, Magnetometer Imperial College London
Tel: +44 20 7594 7757. Mobile: +44 7990 973761.
Email: m.dougherty@imperial.ac.uk

Carolina Martinez - Jet Propulsion Laboratory, Pasadena, California, USA
Tel: +1 (818) 354-9382.
Email: carolina.martinez@jpl.nasa.gov

Notes to editors:

For the latest Enceladus images see
www.nasa.gov/cassini

This includes an image which shows Enceladus, which is just 505 km across (314 miles), is small enough to fit within the length of the UK.

Cassini Scientists will be taking part in the Project Science group meeting at Imperial College from 30th August- 2nd September.

Images
saturn.jpl.nasa.gov
www.nasa.gov/cassini

Listing of all of the Enceladus pictures issued to date
photojournal.jpl.nasa.gov/target/Enceladus?start=0

Cassini Huygens
The Cassini spacecraft is the first spacecraft to explore the Saturn system of rings and moons from orbit. Launched in October 1997 Cassini entered Saturn's orbit on 1st July 2004 and immediately began sending back intriguing images and data.
The European Space Agency's Huygens Probe successfully separated from Cassini on 25th December 2004 and descended through Titan's atmosphere on 14th January 2005, to land on its surface -sending back some amazing images giving us the first close up look at the features of Titan. The sophisticated instruments on both spacecraft are providing scientists with vital data and the best views ever of this mysterious, vast region of our solar system.

Enceladus
Enceladus is a 500 km diameter bright icy moon at a distance of 4 Saturn radii away from Saturn.
The first two flybys of the moon revealed a striking signature in its magnetic field. On the basis of the magnetometer instrument observations a decision was made to modify the spacecraft trajectory for the 14th July encounter to fly much closer to the surface of Enceladus.
The flyby on 14th July provided further evidence to confirm the presence of an atmosphere.
The flybys also revealed close up images of the landscape of Enceladus - showing areas of varying terrain including an area near the south pole with long bluish cracks or faults which have been dubbed 'tiger stripes'.
Further studies following the 14th July flyby reveal evidence for active volcanism on Enceladus with a huge cloud of water vapour found over the south pole, and warm fractures where evaporating ice probably supplies the vapour cloud.

Flybys of Enceladus
Date Distance
17 February 2005 1,167 km (725 miles)
9 March 2005 500 km (310 miles)
14 July 2005 175 km (108 miles)

Future
12 October 2005 49,000 km (31,000 miles)
27 November 2005 108,000 km (67,000 miles)
24 December 2005 94,000 km (58,000 miles)

UK involvement
UK scientists have been involved in the design and development of eight of the eighteen instruments on board Cassini-Huygens (six on Cassini and two on Huygens).
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 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.

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