Author's personal copy Natural radio emission of Jupiter as interferences for radar investigations of the icy satellites of Jupiter B. Cecconi a,Ã , S. Hess b , A. He ´ rique c , M.R. Santovito d , D. Santos-Costa e , P. Zarka a , G. Alberti d , D. Blankenship f , J.-L. Bougeret a , L. Bruzzone g , W. Kofman c a LESIA (UMR 8109), Observatoire de Paris/CNRS-INSU/UPMC/Univ. Denis Diderot, Meudon, F-92195, France b LATMOS (UMR 8190), IPSL/UVSQ/UPMC/CNRS-INSU, Guyancourt, F-78280, France c UJF-Grenoble 1/CNRS-INSU, Institut de Plane´tologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France d CO.RI.S.T.A., Naples, Italy e Space Science Department, Southwest Research Institute, Texas, USA f Institute of Geophysics, University of Texas at Austin, USA g Department of Civil and Environment Engineering, University of Trento, Italy article info Article history: Received 21 December 2010 Received in revised form 13 June 2011 Accepted 20 June 2011 Available online 2 July 2011 Keywords: Jupiter EJSM/Laplace Radio emissions Galilean satellites Radar instrumentation abstract Radar instruments are part of the core payload of the two Europa Jupiter System Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter Ganymede Orbiter (JGO). At this point of the project, several frequency bands are under study for radar, which ranges between 5 and 50 MHz. Part of this frequency range overlaps with that of the natural jovian radio emissions, which are very intense in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of interferences, whereas below this threshold, careful observation strategies have to be investigated. We present a review of spectral intensity, variability and sources of these radio emissions. As the radio emissions are strongly beamed, it is possible to model the visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We have investigated Io-related radio emissions as well as radio emissions related to the auroral oval. We also review the radiation belts synchrotron emission characteristics. We present radio sources visibility products (dynamic spectra and radio source location maps, on still frames or movies), which can be used for operation planning. This study clearly shows that a deep understanding of the natural radio emissions at Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that this radio noise has to be taken into account very early in the observation planning and strategies for both JGO and JEO. We also point out possible synergies with RPW (Radio and Plasma Waves) instrumentations. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction In the frame of the future ESA-NASA EJSM (Europa Jupiter System Mission), instrumental studies have been initiated by ESA to evaluate the technical feasibility and science objectives of the different instrumental packages. The EJSM/Laplace concept is composed of two spacecraft: NASA-led JEO (Jupiter Europa Orbiter) and ESA-led JGO (Jupiter Ganymede). The study of sub- surface layers of Europa and Ganymede through radar sounding is one of the main science objectives of this space mission. Unfortu- nately, the radio environment of Jupiter is dominated by strong natural radio emissions, which can interfere with radar measure- ments near Europa or Ganymede. The jovian radio emissions were discovered by Burke and Franklin (1955). Since then, decades of ground based and space based observations provided a good knowledge of the character- istics of these emissions. Ground based observations are limited by the terrestrial ionospheric cutoff, which reflects out radio waves with frequencies lower than 10 MHz. Space based observa- tions are usually limited at high frequencies because of the limited resources available on a spacecraft. As reviewed by Zarka (1998) and recalled in Figs. 1 and 2, the jovian radio spectrum is composed of several components that will be reviewed in this paper. These radio emissions dominate the galactic background (Cane, 1979), which is usually the major source of noise for planetary radar measurements. The radar instrumentation under study for the EJSM mission is foreseen to operate at frequencies ranging between 5 and 50 MHz. This frequency range can be split into two ranges at  40 MHz. Below that limit, the radio spectrum is dominated by very intense and sporadic cyclotron radio emissions with sources Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/pss Planetary and Space Science 0032-0633/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.pss.2011.06.012 Ã Corresponding author. E-mail address: baptiste.cecconi@obspm.fr (B. Cecconi). Planetary and Space Science 61 (2012) 32–45