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A quiescent magnetosphere for Neptune
Author(s) -
Dessler A. J.,
Sandel B. R.
Publication year - 1989
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl016i008p00957
Subject(s) - magnetosphere , magnetosphere of jupiter , physics , neptune , magnetopause , polar wind , mercury's magnetic field , solar wind , magnetosphere of saturn , geophysics , magnetic dipole , plasma sheet , dipole , astronomy , astrophysics , magnetic field , planet , coronal mass ejection , quantum mechanics
If Neptune has a large magnetic moment, a weak supply of plasma for its magnetosphere, and a magnetic moment that is in near alignment with the planetary spin axis, we argue that, except for a region near the magnetopause, the Neptunian magnetosphere is almost completely quiescent. Because the inner portion of a magnetosphere tends to be shielded from solar‐wind influences, a large magnetosphere would have all latitudes shielded except for a small polar region. If, for example, the equatorial magnetic field at cloudtop levels B o were as large as, say, Jupiter's (4.2 Gauss), and if plasma pressure within the magnetosphere were negligible, the nominal nose distance R m of the magnetosphere would be 74 R N . The shielded region could extend out to 25 R N , which corresponds to a magnetic latitude of nearly 80°. R m varies as B o 1/3 , so the size of the magnetosphere is not very sensitive to the strength of the planetary magnetic field. Also, typical variations in solar‐wind ram pressure do not cause large changes in the size of such a magnetosphere because R m varies as the 6th root of the ram pressure. Standard magnetospheric theory promises that Neptune is a rotationally dominated magnetosphere, so the solar wind is not an effective power source. Zonal wind can contribute to energization of trapped radiation if the dipole is tilted relative to the spin axis. If Neptune's ionosphere and Triton's atmosphere together do not supply more than about 1 kg/sec to the magnetosphere, then, with a spin‐axis‐aligned dipole, the internal power sources for the magnetosphere would be less than 10 9 Watts (less than 1% of the average power utilized by the Earth's magnetosphere). This is consistent with the thus far observed lack of radio and auroral UV emissions. In such a magnetosphere, because they would enjoy a long residence time, non‐relativistic particles could collect to form a substantial radiation belt.