Transcript PPT - Astron

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
• 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=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
• 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 :
 LF cutoff  dayside
peak ionospheric
density
Saturn
Uranus
• 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
C
(ex : N=1, 10 kHz  1 sec)
102
  Saturn’s lightning
with C ≥105 (N=200, 10
104
MHz  25 msec),
without access to LF
cutoff
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 ≥ 1001000
(N=1-10, 10 kHz  1 sec)
C
102
 + Uranus & Neptune
auroral emissions
+ Saturn & Uranus
lightning (including LF
cutoff) with C ≥ 104 (N=10-
104
100, 200 kHz  50-500 msec)
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
C
103
 + possible stronger
stellar wind, focussing
events, …
105
105
107
103
10
1
109
•
Magnetic Radio Bode's Law
•
•
Hot Jupiters ?
• Detectability from the ground (Earth) :
 No solar bursts
/spherics , RFI
mitigation
C
 ≥10-20 MHz
103
105
107
  requires C≥107
(N=1000-10000, 1-10 MHz 
1-10 sec)
109
• Detectability from the Moon :
 ≥1 order of
magnitude better
C
103
(C ≥ 105-6 : N=100, 1-10
MHz  1-10 sec)
105
 + access to less
energetic sources
(C ≥ 106-7 : N>>100)
107
 + access to VLF
(weakly magnetized
bodies)
109
• 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)