Letters to Nature

Nature 415, 994-996 (28 February 2002) | doi:10.1038/415994a; Received 6 August 2001; Accepted 14 November 2001

A nebula of gases from Io surrounding Jupiter

Stamatios M. Krimigis1, Donald G. Mitchell1, Douglas C. Hamilton2, Jannis Dandouras3, Thomas P. Armstrong4, Scott J. Bolton5, Andrew F. Cheng1, George Gloeckler2, K. C. Hsieh6, Edwin P. Keath1, Norbert Krupp7, Andreas Lagg7, Louis J. Lanzerotti8, Stefano Livi1, Barry H. Mauk1, Richard W. McEntire1, Edmond C. Roelof1, Berend Wilken7 & Donald J. Williams1

  1. Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA
  2. Department of Physics, University of Maryland, College Park, Maryland 20742, USA
  3. CNES, 9 Avenue du Colonel Roche -BP 4346, F-31028 Toulouse Cedex 4, France
  4. Fundamental Technologies, 2411 Ponderosa, Suite A, Lawrence, Kansas 66046, USA
  5. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA
  6. Department of Physics, University of Arizona, Tucson, Arizona 85721, USA
  7. Max-Planck-Institut für Aeronomie, D-37191 Katlenburg Lindau, Germany
  8. Bell Laboratories, 600 Mountain Avenue, Building 1E-439, Murray Hill, New Jersey 07974, USA

Correspondence to: Stamatios M. Krimigis1 Correspondence and requests for materials should be addressed to S.M.K. (e-mail: Email: tom.krimigis@jhuapl.edu).

Several planetary missions have reported1, 2, 3, 4 the presence of substantial numbers of energetic ions and electrons surrounding Jupiter; relativistic electrons are observable up to several astronomical units (au) from the planet. A population of energetic (>30 keV) neutral particles also has been reported5, but the instrumentation was not able to determine the mass or charge state of the particles, which were subsequently labelled6 energetic neutral atoms. Although images showing the presence of the trace element sodium were obtained7, the source and identity of the neutral atoms—and their overall significance relative to the loss of charged particles from Jupiter's magnetosphere—were unknown. Here we report the discovery by the Cassini spacecraft of a fast (>103 km s-1) and hot magnetospheric neutral wind extending more than 0.5 au from Jupiter, and the presence of energetic neutral atoms (both hot and cold) that have been accelerated by the electric field in the solar wind. We suggest that these atoms originate in volcanic gases from Io, undergo significant evolution through various electromagnetic interactions, escape Jupiter's magnetosphere and then populate the environment around the planet. Thus a 'nebula' is created that extends outwards over hundreds of jovian radii.