Acknowledgement. We thank Science for their permission to use an excerpt from:

Ness, N. F., et al. Magnetic fields at Neptune. Science 246, (4936) 1473-1478. (Excerpt from pp. 1476-1477).

Copyright AAAS, December 15, 1989.

Magnetic Fields at Neptune

Satellite and ring interactions. The Voyager encounters at Jupiter, Saturn, and Uranus have shown that their moons and rings are very effective absorbers of magnetically trapped charged particles in their radiation belts. This is also the case at Neptune, where such absorption features have been detected (13, 14). All of the new moons and the rings are located inside 4.75 R_N and will therefore be characterised by complex absorption features due to the complicated near magnetic field of Neptune. The OTD-derived L value for V2 and Triton outside 4 R_N is plotted as a function of time in Fig. 7. The L value for Triton sometimes exceeds 30 R_N, implying that Triton may be located well outside the inner magnetosphere of Neptune (R < 15 R_N) and indeed on field lines connected to the polar cusp or deep tail regions.

The interaction between the atmosphere and ionosphere of Triton (15, 16) and Neptune's magnetosphere leads to the creation of a modest plasma torus (17) with large dimensions, due to the large tilt of the global magnetic field of Neptune. Preliminary inspection of the magnetic field data, limited by as yet unresolved spacecraft attitude uncertainties around Triton CA (from 237/0700 to 237/1100) shows a stable magnetospheric field of Neptune but no signature attributable to Triton. In fact, in the assumed absence of an internal magnetic field of Triton, the atmosphere ionosphere system requires an Alfven wing interaction (18) at sub-Alfvenic Mach numbers, M_A. The sub-Alfvenic character of the flow is suggested by the absence of strong centrifugal instability of the magnetosphere near Triton's orbit.

The detectability of any Alfven wings of Triton depends strongly on the location and r and distance of V2 from the wing. For a fully developed Alfven wing, such as at Io (19), the relative disturbance field is given by Neubauer (20) as:

|DeltaB| / B_0 = M_A (R_w/r)^2 [1]

where B_0 is the undisturbed field, R_w is the radius of the wing, and r is the distance from the cylindrical wing. Hence, the detectability depends strongly on the orientation of the global magnetic field. Unfortunately, in this regard the geometry at V2 flyby was unfavorable because of the large tilt of the OTD.

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Last updated Feb-27-1997