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The magnetic field and the magnetosphere of the planet Mars

Planetary and Space Science
Publication Date
DOI: 10.1016/0032-0633(91)90077-n
  • Astronomy
  • Mathematics
  • Physics


Abstract The Phobos-2 plasmagrams and magnetograms measured on the day-side of Mars are used to identify the shock front, the transition region and magnetopause crosses in the same way as these boundaries are identified near the Earth's magnetosphere. The Martian magnetic moment, M M = (1.35 ±0.03) × 10 12 T m 3, is estimated from the gas dynamics equations and plasma data. Subdivision of the measured field into parts of external and internal origin, and the estimated Gauss coefficients of the dipole field allow us to determine M M = (1.22 ± 0.07) × 10 12 T m 3. The dipole axis is inclined at an angle θ = 12 ± 3° to the rotation axis and the north magnetic pole is in the Southern Hemisphere. This agrees with the most reliable values, M = (1.4 ± 0.6) × 10 12 and 1.5 × 10 12 T m 3, φ ⩽ 15° and the dipole polarity determined earlier from Mars-2, 3 and 5 data (Slavin and Holzer, 1982, J. geophys. Res. 87, 10285 ; Dolginov et al., 1984a,b, Cosmic Res. XXII, 3, 5). The energy density of the intrinsic magnetic field, B i 2/8 πr = 12 × 10 −10erg, exceeds the energy density of the ions, nkT i = 0.9 × 10 −10erg, by 13 times at 870 km altitude. The magnetic field, not the ionosphere, is the real obstacle to solar wind near Mars when P sw ⩽ 5 × 10 −9 dyn cm −2. An analysis of available magnetic and plasma data, measured in the solar wind and on the night-side, at the ellipsoidal and circular orbits ( r = 2.96 R M), during periods of low and high solar wind activity, reveal the following : (1) the ratios of the flux, φ x , in the tail and the transverse B ⊥ inter-planetary magnetic field (IMF) components— φ x : B ⊥ —differ considerably for weak intensity B ⊥, which is not expected for a totally induced tail; (2) the dependence of the tail topology upon : the planetary corotation with the inclined magnetic dipole ; the process of reconnection between the intrinsic dipole field and the B z -component of IMF on the dayside ; solar wind pressure, P sw; (3) the situations with identical P swand B z -orientation are different at low ( Phobos-2) and higher ( Mars- 5) latitudes. The solar wind interaction with the intrinsic magnetic field of Mars agrees, to the first approximation, with the theoretical concepts considered by Rassbach et al. (1974, J. geophys. Res. 79, 1125) and Breus et al. (1989, Geophys. Res. Lett. 94, 2375)

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