Planets and Solar System Science at Low Frequencies Philippe Zarka LESIA, CNRS-Observatoire de Paris France [email protected] Towards a European Infrastructure for Lunar Observatories Bremen, 22-23/3/2005 - EADS / ASTRON / Radionet
Feb 07, 2016
Planets and Solar System Scienceat Low Frequencies
Philippe ZarkaLESIA, CNRS-Observatoire de Paris
Towards a European Infrastructure for Lunar ObservatoriesBremen, 22-23/3/2005 - 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 RE)
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=32/8
• Antenna effective area :A = k2 with k = 3/8 ~1/8 for a short dipole,
k ~N/8 for N dipolesA ~ 2 ~1/k ~ 8/NLOFAR ~ 104 dipoles
• Jovian radio emissions (near opposition) :
Solar wind / magnetosphere interaction (auroral emissions)
Io/magnetosphere interaction
Io torus
+ Synchrotron from radiation belts (HF)
Radiosources inJupiter's environment
Io-Jupiter plasma interaction
• + Saturn, Uranus, Neptune auroral emissions :
Saturn
UranusNeptune
• + Saturn, Uranus atmospheric lightning :
SaturnUranus
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 ≥105 (N=200, 10 MHz 25 msec),without access to LF cutoff
C
102
104
106
• 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 ≥ 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
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 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
Magnetic Radio Bode's Law
••
Hot Jupiters ?
•
• Detectability from the ground (Earth) :
C
103
105
107
109
No solar bursts /spherics , RFI mitigation
≥10-20 MHz
requires C≥107
(N=1000-10000, 1-10 MHz 1-10 sec)
• 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)
• 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
possible active sounding of Terrestrial magnetosphere (~IMAGE)