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

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)

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

LF Earth environment :  AKR day/night (at 60 R E )  Thermal noise (≠flux)  Galactic background  Ionospheric LF cutoff  Solar wind LF cutoff  Solar emission/ burst/storm  Spherics

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 ~ 10 4 dipoles

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

Radiosources in Jupiter's environment

Io-Jupiter plasma interaction

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

+ Saturn, Uranus atmospheric lightning : Saturn Uranus  LF cutoff  dayside peak ionospheric density

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 ≥10 5 (N=200, 10 MHz  25 msec), without access to LF cutoff C

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

Detectability from the Moon :   all Jovian emissions + Saturn auroral emissions with C ≥ (N=1-10, 10 kHz  1 sec)  + Uranus & Neptune auroral emissions + Saturn & Uranus lightning (including LF cutoff) with C ≥ 10 4 (N= , 200 kHz  msec) C

 Long-term magnetospheric radio observations (+ multi- correlations)

 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

 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

Extrasolar Jupiter-like radio emissions at 10 pc range :  Flux up to  10 5 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

Magnetic Radio Bode's Law Hot Jupiters ?

Detectability from the ground (Earth) : C  No solar bursts /spherics, RFI mitigation  ≥10-20 MHz   requires C≥10 7 (N= , 1-10 MHz  1-10 sec)

Detectability from the Moon : C  ≥1 order of magnitude better (C ≥ : N=100, 1-10 MHz  1-10 sec)  + access to less energetic sources (C ≥ : N>>100)  + access to VLF (weakly magnetized bodies)

NB :  Angular resolution required ~1°-10°  D = 6-60 ( kHz ; 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

 possible active sounding of Terrestrial magnetosphere (~IMAGE)