Knowledge of the magnetization of planetary bodies allows far--reaching conclusions on their formation processes, and the conditions in the solar nebular at that time. Based on magnetic field measurements during the descent and subsequent triple landing of the ROSETTA lander PHILAE on comet 67P/Churyumov--Gerasimenko, we show that no global magnetic field was detected within the limitations of analysis. The ROMAP suite of sensors measured an upper magnetic field magnitude of less than 2 nT at the cometary surface at multiple locations with the upper specific magnetic moment being < 3.1·•10 --5 Am 2 /kg for meter--size homogeneous magnetized boulders and the maximum dipole moment of 67P/Churyumov--Gerasimenko is 1.6·•10 8 Am 2 . We conclude that on this scale magnetic alignment in the pre--planetary nebular is of minor importance.One Sentence Summary: High--precision magnetic field measurements obtained during the triple landing of ROSETTA's lander PHILAE demonstrate that the Jupiter family comet 67P/Churyumov--Gerasimenko is unmagnetized (<3.1·•10 --5 A m 2 /kg).Main Text: Comets are believed to have been formed in the outer solar nebula beyond the snow line, where icy aggregates can grow in size to form larger bodies (1--3). Both the Kuiper belts as well as the Oort cloud are possible reservoirs of comets, with different processes leading to their formation (3). The dust--to--ice ratio of comets is of the order 1 (4, 5). Thus, a large fraction of cometary material is refractory material. Analysis of Stardust samples indicates a high contribution of Fe to this refractory material (6, 7). Up to 1% of the Fe content can be present as magnetite. Processes like accretional remanent magnetization (8) or detrital remanent magnetization (9) are possible candidates to form larger scale magnetic dust grains and cometesimals. These in turn allow the possibility for a comet to possess a larger scale remanent magnetic field.Detection of any cometary magnetization is difficult as a dipole field decreases with the cube of the distance from the object. Global magnetization of small solar system bodies can be detected either by spacecraft flybys or direct measurements on the surface. Whereas the flybys of the Galileo and Deep Space spacecraft at asteroids 951 Gaspra and 9969 Braille suggested the possibility of notable magnetization of these bodies (10,11), the distant flybys of the ROSETTA spacecraft (12) at asteroids 2867 Steins and 21 Lutetia provided an upper limit on the specific magnetic moment of 10 --6 Am 2 /kg (13, 14).Magnetic field measurements obtained during the flyby of the GIOTTO spacecraft at comet 1P/Halley offered an opportunity to estimate cometary magnetization as they revealed an almost magnetic field free (<50 pT) region around the nucleus (16,17). Taking into account the closest approach distance of 596 km to Halley's nucleus this corresponds to a formal dipole magnetic moment of < 5·•10 13 Am 2 or an upper specific magnetic moment of < 0.25 Am 2 /kg, an unreasonably large value indicating the l...
[1] A self-consistent global three-dimensional kinetic study of Mercury's magnetosphere is carried out examining waves and instabilities generated by ion temperature anisotropy and plasma flow. The overall structure of Mercury's upstream bow shock and magnetosheath are qualitatively very similar to those of Earth. Beam-generated long-wavelength oscillations are present upstream of Mercury's quasiparallel bow shock, whereas large-amplitude mirror waves develop downstream of the quasi-parallel bow shock in the magnetosheath. A train of mirror waves forms also downstream of the quasi-perpendicular bow shock. A velocity shear near the magnetopause can lead to formation of vortex-like structures. The magnetospheric cavity close to the planet's equatorial plane is filled with ions much hotter than the solar wind protons. A drift-driven plasma belt close to the equator is present in the model and contains plasma with high-temperature anisotropy, and the loss cone for charged particles in this region is large. The belt may cause diamagnetic effects superimposed on the planet's internal magnetic field and can interact with Mercury's magnetopause. Citation: Trávníček, P. M., P. Hellinger,
[1] Results of two global three-dimensional hybrid simulations of the solar wind interaction with the Hermean magnetosphere are presented for southward and northward interplanetary magnetic field (IMF) orientations. Important dawn-dusk asymmetries of the Hermean bow shock and magnetosheath are observed depending on the IMF orientation. For the southward IMF, the dawnside has a thicker magnetosheath with higher b values and slower bulk velocities compared to the duskside, whereas for the northward IMF, the duskside has a thicker and higher b magnetosheath with slower bulk velocities. Mirror mode activity consequently appears at the dawnside for the southward IMF and at the duskside for the northward IMF. A mechanism for the bow shock and magnetosheath asymmetries is proposed and discussed in the context of the Hermean and terrestrial magnetosheaths.
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