RPC Meeting, Braunschweig Sept. 2010
Messung planetarer und interplanetarer Magnetfelder Sommersemester 2014
Lehrveranstaltung: 440.413
Dr. Konrad Schwingenschuh/Ö[email protected]
23. Mai 2014 bis 28. Mai 2014
Folien © Dr. Konrad Schwingenschuh
RPC Meeting, Braunschweig Sept. 2010
Globale elektrische Leitfähigkeit: Allgemeines
Magn. Fluktuationen und Sprünge des interplanetaren Magnetfeldes werden durch die elektr. Leitfähigkeit von Himmelskörpern durch magn. Diffusion gedämpft. Die Bestimmung erfolgt mittels Orbiter- und Lander-Magnetometer. Die Abschätzung der Leitfähigkeit erfolgt durch die Relation
Sigma = tau / (mu_0 * L^2) ; tau ... char. Diffusionszeit [s]; L ... Durchmesser des Himmelskörpers (char. Länge)
Beispiel: Rosetta (Kometenkern), Galileo (mögliche Ozeane auf Jupitermonden Europa, Ganymede, Callisto), Mond (Apollo 12 und Explorer 35)
RPC Meeting, Braunschweig Sept. 2010
Global magnetic and electric properties of a cometary nucleus: Global magnetic and electric properties of a cometary nucleus: ROSETTA combined orbiter and lander magnetic field experiment ROSETTA combined orbiter and lander magnetic field experiment
RPC Meeting, Braunschweig Sept. 2010
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Magnetic properties of asteroids and cometsMagnetic properties of asteroids and comets
- previous magnetic field investigations: - Gaspra 1993 (magnetic moment?) - NEAR@433EROS_2000 (no significant magnetic moment
found) - ROSETTA Steins 2008 (no evidence for magnetization
found) -ROSETTA-Lutetia 2010 (no evidence for an intrinsic field)
- magnetized dust & accretional remanence: - Nüboldt 2000 -Weiss2012
- ROSETTA 2014: remanent magnetization in the solar nebula
Resume.fol
RPC Meeting, Braunschweig Sept. 2010
Global electrical Global electrical conductivityconductivity - dual point magnetic field and global electrical conductivity [Dyal
1973] - electromagnetic induction in the cometary nucleus - study of time varying interplanetary magnetic field (Constantinescu
2012)
References 1. Dyal, P. and W.P. Curtis, Global Electromagnetic Induction in
the Moon and Planets, Physics of the Earth and Planetary Interior, 7 (1973) 251-265
2. Constantinescu-et al.-2012, PSS-On the possibility to determine the electrical conductivity of 67PCG from ROSETTA magnetic field observations
RPC Meeting, Braunschweig Sept. 2010
Combined measurement of ROMAP and RPC
Before descent
During descent
After descent
RPC Meeting, Braunschweig Sept. 2010
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ROMAP – Reminder!ROMAP – Reminder!
Magnetometer2000nT range, 0.05nT resolution, 64Hz
Pressure SensorsPirani: 10-3 –10 mbar
Penning: 10-8 –10-4 mbar
Electrostatic Analyzerions: 40...8000eV; electrons: 0.3...4200eV
Faraday Cupresolution 5x10-12 – 4x10-10
RPC Meeting, Braunschweig Sept. 2010
Descent OperationDescent Operation
Why magnetic properties of a comet are interesting Magnetization of processed and non-processed material is very different Known examples are Meteorites and Asteroids Magnetization could explain gap in planetary formation (10-3 … 101m)
Determination of magnetic properties of CG
Aubrite (non processed)ALHA 78 113 Magnetization: 2.8mAm²/kg
Diogenite (processed)MIL 07 001Magnetization: 0.05mAm²/kg
RPC Meeting, Braunschweig Sept. 2010
Descent OperationDescent Operation
Why characterization can be done during descent only Direct measurements of magnetization can be done at different distances Drop off profile gives information about homogeneity magnetic field on surface is proportional to NRM
Determination of magnetic properties of CG
Assumptions:Diameter: 5kmDensity: 1.0g/cm3NRM: 0.1mAm2/kg
a - c: aligned dipolesd – e: randomly distributedNo. of dipoles: 1 103 106 103 106
B vs. altitude
RPC Meeting, Braunschweig Sept. 2010
FSS / LTSFSS / LTS
Onset & evolution of s/w interaction Measurement Scenario
switching on time: 4 hours centered about noon Optional (LTS): 8 hours including night ROMAP in Surface Mode
Constraints No common operation with “magnetic active” experiments Favored measurement partners: Concert, Civa, Rolis, Sesame,
Mupus Operation of RPC MAG mandatory
Resources Operation time: 4 hours (MAG & SPM) Power consumption: 4 Watt Data volume: 60 kbyte/hour
RPC Meeting, Braunschweig Sept. 2010
LTSLTS
Combined E- and B-field & P-measurement
Conductivity investigation using variation analysis Variation of B field (ROMAP/RPC) and E field (SESAME)
shall be used to investigate global conductivity High resolution data (64Hz) necessary, previous measurement
helpful for planning effective operation
Lander Day and Night pressure measurement Promises high scientific return about outgassing behavior Uncertainty: Penning functionality
RPC Meeting, Braunschweig Sept. 2010
SummarySummary
Prior Separation (ICEP) ROMAP supports RPC MAG measurements
to separate s/c interferences
During Descent (SDL) RPC-MAG supports ROMAP measurement
to separate temporal variations from CG signature
On Surface (FSS and LTS) Combined measurement of RPC and ROMAP
to separate local and temporal field variation
And determine the global electrical conductivity
Magnetized dust and accretional magnetism