Venus Plasma Boundaries and Ionospheric Plasma Escape
Swedish Institute of Space Physics
New results from the ASPERA 4 plasma and energetic neutral atom instrument on Venus Express will be presented. The focus will be on the solar wind interaction with Venus, and the corresponding escape of planetary ions. An important objective of ASPERA 4 is to study the composition, energy and intensity of the plasma escaping from Venus. As expected, the outflowing ions have a composition consistent with a source region located in the topside ionosphere of Venus. The outflow consists of primarily atomic species such as O+, H+, and He+. The molecular ion outflow is low, much lower than on Mars. Of particular interest is also the flow properties and ion composition at the contact boundaries between the solar wind and the induced magnetosphere of Venus. Outer boundaries such as the Bow shock and the induced magnetosphere boundary (IMB), display similar properties like on Mars. A major difference between Mars and Venus is the central tail, possibly related with the lack of magnetized regions on Venus.
Preliminary analysis lends support for a substantial low-energy mass escape on Venus. The escape flow, dominated by O+, appears more like a tapered low-energy ionospheric plasma extension into the tail, resembling extensions from the cometlike features reported by Brace et al., (1987). The average velocity of the flow at a downtail distance of ?2 Venus radii is a few tens of km/s.
Created 2007-01-10 13:43:17 by Mats HolmstrÃ¶m Last changed 2007-01-10 13:43:53 by Mats HolmstrÃ¶m