15 Apr 2010
(Source: Royal Astronomical Society)
Observations of how Saturn's moon Enceladus interacts with its environment show it leaves a complex pattern of ripples and bubbles in its wake. Sheila Kanani will be presenting the results at the RAS National Astronomy Meeting in Glasgow on Thursday 14th April.
Enceladus sits deep within Saturn's magnetosphere, which is filled with electrically charged particles (plasma) originating from both the planet and its moons. The Cassini spacecraft has made nine flybys of the mysterious sixth-largest moon since 2005. The closest of these have taken the spacecraft's suite of instruments just 25 km from Enceladus's surface, which many scientists believe conceals a saline ocean. Heated vents at the south pole of the moon release a plume of material, consisting mainly of icy grains and water vapour, into space.
Measurements from the Cassini Plasma Spectrometer (CAPS) and the Magnetospheric IMaging Instrument (MIMI) show that both the moon and its plume are continuously soaking up the plasma, which rushes past at around 30 kilometres per second, leaving a cavity downstream. In addition, the most energetic particles which zoom up and down Saturn's magnetic field lines are swept up, leaving a much larger void in the high energy plasma. Material from Enceladus, both dust and gas, is also being charged and forming new plasma.
Now, Ms Kanani and a team at UCL's Mullard Space Science Laboratory have discovered mysterious spiky features in the CAPS data that present a complex picture of readjustment downstream from Enceladus.
"Eventually the plasma closes the gap downstream from Enceladus but our observations show that this isn't happening in a smooth, orderly fashion. We are seeing spiky features in the plasma that last between a few tens of seconds and a minute or two. We think that these might represent bubbles of low energy particles formed as the plasma fills the gap from different directions," said Ms Kanani.
Since Cassini arrived at Saturn, it has been building up a picture of the vital and unexpected role that Enceladus plays in Saturn's magnetosphere.
Enceladus may play a role similar to Jupiter's moon Io, which pumps plasma into Jupiter's environment. A picture of plasma adjustments in the wake of Enceladus could provide clues to how plasma gets transported around the Saturnian environment.
"Enceladus is the source of most of the plasma in Saturn's magnetosphere, with ionised water and oxygen originating from the vents forming a big torus of plasma that surrounds Saturn. We may see these spiky features in the wake of Saturn's other moons as they interact with the plasma but, to date, we have only studied Enceladus in sufficient detail," said Ms Kanani.
Mullard Space Science Laboratory
University College London
Holmbury St. Mary, Dorking, Surrey
Tel: +44 (0)7947308616
Artist's impression of the Cassini spacecraft making a close pass by Saturn's inner moon Enceladus to study plumes from geysers that erupt from giant fissures in the moon's southern polar region.
Copyright 2008 Karl Kofoed/NASA
Cassini Huygens is a joint endeavour of ESA, NASA and the Italian space agency, Agenzia Spaziale Italiana (ASI). For more information, see: http://saturn.jpl.nasa.gov
The Cassini Plasma Spectrometer (CAPS) is led by the South West Research Institute. The instrument measures the energy and electrical charge of particles such as electrons and protons that the instrument encounters. The instrument is used to study the composition, density, flow, velocity, and temperature of ions and electrons in Saturn's magnetosphere. For more information, see: http://caps.space.swri.edu/caps/index.shtml
THE RAS NATIONAL ASTRONOMY MEETING 2010
The RAS National Astronomy Meeting 2010 will take place from 12-16th April at the University of Glasgow. The conference is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. NAM2010 (www.astro.gla.ac.uk/nam2010/) is principally sponsored by the Royal Astronomical Society (RAS) and the University of Glasgow.
THE ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
THE UNIVERSITY OF GLASGOW
The University of Glasgow (founded 1451) is one of the world's top 100 research universities with more than 70 per cent of its research rated as world-leading or internationally excellent. The Physics and Astronomy Department is one of the top four in the UK's major research-intensive universities, the Russell Group.
The conference comes to Glasgow during the 250th anniversary year of the founding of the Regius Chair of Astronomy at the University of Glasgow, first held by astronomer and meteorologist Alexander Wilson in 1760. The present incumbent is Prof. John Brown, 10th Astronomer Royal for Scotland.