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Planets and Solar System Science at Low Frequencies Philippe Zarka

Planets and Solar System Science at Low Frequencies Philippe Zarka LESIA, CNRS-Observatoire de Paris France philippe.zarka@obspm.fr Towards a European Infrastructure for Lunar Observatories Bremen, 22-23/3/2005 - EADS / ASTRON / Radionet. Limitations of ground-based LF radioastronomy :

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Planets and Solar System Science at Low Frequencies Philippe Zarka

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  1. Planets and Solar System Science at Low Frequencies Philippe Zarka LESIA, CNRS-Observatoire de Paris France philippe.zarka@obspm.fr Towards a European Infrastructure for Lunar Observatories Bremen, 22-23/3/2005 - EADS / ASTRON / Radionet

  2. Limitations of ground-based LF radioastronomy : •  RFI (man-made, lightning spherics) • Ionospheric cutoff (~10 MHz) + propagation effects (≤30 MHz) • Sky background (fluctuations) •  IP, IS scintillations • (Solar radio emissions)

  3. Limitations of LF radioastronomy in Earth orbit : •  RFI (man-made, lightning spherics) • Auroral Kilometric Radiation • Sky background (fluctuations) •  IP, IS scintillations • (Solar radio emissions)

  4. Solar emission/ burst/storm • Spherics • LF Earth environment : • AKR day/night (at 60 RE) • Thermal noise (≠flux) • Galactic background • Ionospheric LF cutoff • Solar wind LF cutoff

  5. Galactic background for a short dipole antenna, i.e. with =8/3, A=32/8 • Antenna effective area : • A = k2 with k = 3/8 ~1/8 for a short dipole, • k ~N/8 for N dipoles • A  ~ 2 ~1/k ~ 8/N • LOFAR ~ 104 dipoles

  6. Jovian radio emissions (near opposition) : • Solar wind / magnetosphere interaction (auroral emissions) • Io/magnetosphere interaction • Io torus • + Synchrotron from radiation belts (HF)

  7. Radiosources in Jupiter's environment

  8. Io-Jupiter plasma interaction

  9. + Saturn, Uranus, Neptune auroral emissions : Saturn Uranus Neptune

  10. LF cutoff  dayside peak ionospheric density • + Saturn, Uranus atmospheric lightning : Saturn Uranus

  11. Detectability from the ground (Earth) : • In absence of solar bursts & spherics • In absence of RFI / after successful mitigation •  ≥10-20 MHz •  Jovian DAM with C=(dipole/)(b)1/2~N(b)1/2 ≥100 (ex : N=1, 10 kHz  1 sec) •  Saturn’s lightning with C ≥105(N=200, 10 MHz  25 msec), without access to LF cutoff C 102 104 106

  12. Moon : • Shielding of RFI, spherics, AKR, Solar emissions • Only limitation to sensitivity = sky background fluctuations • Ionospheric LF cutoff <<500 kHz

  13. Detectability from the Moon : •  all Jovian emissions+ Saturn auroral emissions with C ≥ 100-1000 (N=1-10, 10 kHz  1 sec) •  + Uranus & Neptune auroral emissions + Saturn & Uranus lightning(including LF cutoff) with C ≥ 104(N=10-100, 200 kHz  50-500 msec) C 102 104 106

  14. Long-term magnetospheric radio observations (+ multi- correlations)

  15. Variabilities/periodicities  magnetospheric dynamics (role of SW, planetary rotation, satellite interactions, Io volcanism, short-lived bursts, substorms ?…) •  planetary rotation period •  B anomalies + secular variations •  Io torus probing (nKOM+Faraday effect) •  SW monitoring from 1 to 30 AU

  16. Saturn/Titan interaction (+other satellites ?) SW influence, substorms ? • Uranus & Neptune auroral emissions observed only once by Voyager 2 ! • Lightning : long-term monitoring, correlation with optical observations, planetary comparative meteorology

  17. Extrasolar Jupiter-like radio emissions at 10 pc range : • Flux up to  105 Jupiter’s strength for magnetized hot Jupiters with solar-like stellar wind input, or unmagnetized hot Jupiters in interaction with strongly magnetized star • + possible stronger stellar wind, focussing events, … C 103 105 107 109 105 103 10 1

  18. • Hot Jupiters ? Magnetic Radio Bode's Law • •

  19. Detectability from the ground (Earth) : • No solar bursts /spherics , RFI mitigation • ≥10-20 MHz •  requires C≥107 (N=1000-10000, 1-10 MHz  1-10 sec) C 103 105 107 109

  20. Detectability from the Moon : C 103 105 107 109 • ≥1 order of magnitude better (C ≥ 105-6 : N=100, 1-10 MHz  1-10 sec) • + access to less energetic sources (C ≥ 106-7 : N>>100) • + access to VLF (weakly magnetized bodies)

  21. NB : • Angular resolution required ~1°-10°  D = 6-60  (18-180 km @ 100 kHz ; 1.8-18 km @ 1 MHz) • if detectability of exo-planetary radio emissions  same for solar-like stellar radio emissions • complementarity to ground-based LOFAR • difficult from space • weak scattering/broadening effects at sources distances <a few 10’s pc

  22. possible active sounding of Terrestrial magnetosphere (~IMAGE)

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