Induced magnetosphere of the Moon. 2. Experimental results from Apollo 12 and Explorer 35

Journal Article · Sat Sep 01 04:00:00 EDT 1973 · J. Geophys. Res., v. 78, no. 25, pp. 5437-5448

DOI:https://doi.org/10.1029/JA078i025p05437· OSTI ID:4307527

Smith, B F; Colburn, D S; Schubert, G; Schwartz, K; Sonett, C P

The asymmetric lunar electromagnetic induction theory of Schubert et al. (1973a) is tested by using data from Apollo 12 Lunar Surface Magnetometer and from the Ames magnetometer on Explorer 35. The comparison of data and theory shows that the Moon displays an induction asymmetry due to the flow of the solar wind and the formation of the diamagnetic cavity on the darkside, i.e., the component transfer functions are found to depend on local time. Vacuum theory is a poor description of the darkside induction; symmetric plasma confinement theory applied to the frontside also is incorrect, but the errors introduced are smaller than for the darkside. It is inferred that the induced field forms a magnetosphericlike configuration, with the field confined mostly to the crust of the Moon. Although the magnetospheric spectrum is time dependent, for all frequencies examined, the distance tnaveled by the solar wind ls so large that a quasi-static magnetospheric configuration can be assumed. The differential power spectrum of the interplanetary magnetic field that excites the Moon is compared with the resulting induction spectmm, which has a linear differential power frequency dependence over the frequency range 2 x 10/sup -4/ to 2 x 10/sup -2/ Hz, falling off on either side of these limits. The integrated power in this band is about 5 gamma /sup 2/ for the interplanetary field local north- south component and about 12 gamma /sup 2/ for the induced spectrum of this component on the lunar surface. Calculated magnetic field line configurations are shown for the Moon immersed in a magnetic disturbance field along, perpendicular, and at 45 deg to the solar-wind direction. Current systems on the lunar sunlit hemisphere and cavity boundary are also shown. Previous estimates of the deep conductivity, based on inversion of dayside data, are not grossly affected by the presence of the asymmetry. The lunar magnetospheric configuration is expected to be typical of the fields induced by the solar wind in all planetary bodies, e.g., Mercury, that lack atmospheres and internal fields. (auth)

• Research Organization: Ames Research Center, Moffett Field, CA
• Sponsoring Organization: USDOE
• NSA Number: NSA-29-025014
• OSTI ID: 4307527
• Journal Information: J. Geophys. Res., v. 78, no. 25, pp. 5437-5448, Journal Name: J. Geophys. Res., v. 78, no. 25, pp. 5437-5448; ISSN JGREA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

*MOON-- MAGNETIC FIELDS
*SOLAR WIND-- INTERACTIONS
ASYMMETRY
INTERPLANETARY SPACE
N56400* --Physics (Astrophysics & Cosmology)--Solar Phenomena
PLASMA