The electrodynamics of the direct interaction of the solar wind with the atmospheres of non-magnetic planets

[摘要] A model for the direct interaction of the solar wind with the atmosphere of a non-magnetic planet is reviewed. In this model the magnetized solar wind acts as a dynamo and induces currents in the planetary ionosphere. A model for the dynamo mechanism is developed and used to calculate current distributions on Mars and Venus. The requirement that these currents be of such a magnitude as to exclude the shock-compressed interplanetary magnetic field from the ionosphere determines the position of the ionopause. The ionopause altitude so calculated depends on the specific model atmosphere adopted for the calculations. For Mars, an ionopause altitude at the subsolar point is predicted to be in the range 3 km to 45 km. No ionopause has yet been observed on Mars. For Venus, the range is 35 km to 7 km which is compatible with the plasmapause observed at 5 km by Mariner 5. The addition of photoions to the solar wind flow is important to the overall interaction model since the mass fraction added to the solar wind flow cannot exceed a certain critical value. The total rate of addition of ions to the flow and the distribution of these ions in the planet's wake are calculated. Mass loss rates of 8 gm/sec for Mars and 12 gm/sec for Venus are found, and these are in reasonable agreement with loss rates calculated from gas dynamic arguments (Michel, 1971). Additional aeronomical effects of the solar wind interaction are also considered.

[发布机构] Rice University