The Plasma Environment of Comets

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138863/1/rog199129s2976.pd

Magnetic field measurements during the ROSETTA flyby at asteroid (21) Lutetia

On July 10, 2010, the ROSETTA spacecraft performed a flyby at asteroid (21) Lutetia at a solar distance of 2.72 AU. The spacecraft�asteroid distance at closest approach was 3120 km. The magnetometers onboard ROSETTA were operating but did not detect any conclusive signature of the asteroid. Any magnetic field signature which could possibly be attributed to the asteroid was below 1nT. Consequently an upper limit for the global magnetic properties of asteroid (21) Lutetia could be derived: maximum dipole moment r1:0 1012 Am2, global maximum magnetization r2:1 103 A=m, specific moment r5:9 107 Am2=kg. Draping of magnetic fields around the nucleus was sought, but evidence for this could not be clearly identified in the data. Plasma simulations taking into account the estimated upper limit of the magnetization and possible outgassing revealed interesting structures very close to the asteroid.The results obtained at Lutetia are contrasted with the results of other asteroid fly by results

Calibration of flux-gate magnetometers using relative motion

A simple analytical mmodel for the calibration of a flux-gate magnetometer using relative sensor motion in a constant magnitude magnetic field (B) is presented. Sensor motion is parametrized in terms of elementary rotations about one axis. The number of elementary rotations constitutes the number of degrees of freedom of the motion. A generalization is performed by investigating cases with known/unknown B, one/several different values of B, one/several degrees of freedom. The maximum number of calibration parameters, which can be determined in each case, is established. The conclusion is that the determination of all calibration parameters, i.e. an absolute calibration of the instrument is already possible if the relative motion has at least two degrees of freedon at a known, constant B value. Two experimental applications of the model are described briefly

Stellar winds and planetary bodies simulations: Magnetized obstacles in super-Alfvénic and sub-Alfvénic flows

Most planetary bodies are moving in the solar wind, in a stellar wind, or in a plasma flow within the magnetosphere of a planet. The interaction of the body with the flowing plasma provides us with various interaction types, which mainly depend on the flow speed, the magnetization of the body, its conductivity, the presence of an ionosphere, and the size of the body.We establish two cornerstones representing highly magnetized obstacles embedded in a super Alfvénic and sub-Alfvénic plasma. Those two cornerstones complete the two cornerstones defined in our previous study on inert obstacles in super-Alfvénic and Sub Alfvénic regimes. Tracking the transitions between these cornerstones enable better understanding of the feedback of the obstacle onto the plasma flow. Each interaction is studied by means of the hybrid model simulation code AIKEF. The results are summarized in three dimensional diagrams showing the current structures, which serve as a basis for our descriptions. We identify the major currents such as telluric, magnetosonic, Chapman Ferraro, and bowshock currents as the signatures of the particular state of development of the interaction region. We show that each type of interactions can be identified by studying the shape and the magnitude of its specific currents