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Around Venus the planetary ionosphere is directly exposed to the shocked solar wind. The interaction takes place in a broad region surrounding the dayside ionosphere, called the mantle, where the shocked solar wind plasma and the plasma of planetary origin have equally important roles. In this paper both the experimentally determined characteristics and the microphysics of the mantle are discussed in detail. It is shown that as a result of the interaction between the two plasma populations, a modified two-stream instability develops, and waves are excited with a frequency of a few times the lower hybrid frequency. The polarization of the waves is almost perpendicular to the magnetic field. The stabilization of the higher-frequency part of the wave spectrum is the result of transverse wave convection in the particular sheet-like geometry of the mantle. The interaction of these waves with planetary ions and electrons is described within the framework of a nonlinear model in which the saturation of the modified two-stream instability is due to induced scattering of the waves on cold planetary ions. The effective collision frequency between the shocked solar wind protons and planetary ions is also calculated; it is shown how this leads to ion pick up and heating. Other macroscopically observable effects of these processes are electron acceleration along the magnetic field and ionospheric heating. The experimental data collected in the dayside mantle of Venus by the instruments carried onboard the Pioneer Venus Orbiter are compared to our model. It is believed that the observations support the scenario presented. Usw/•ci "' 10 3 km, where Usw "' 100 km S -1 is the solar wind velocity in the mantle and ftc• is the gyrofrequency of the oxygen ions. The typical distance at which E x B pickup takes place is *rUsw/Dc•, and accordingly the pickup ions leave the 21,289 21,290 SHAPIRO ET AL.: SHOCKED SOLAR WIND AND VENUS PLANETARY IONS mantle region. The plasma population of the mantle, which governs its local microphysics, consists of the counterstreaming shocked solar wind and the ionospheric cold plasma. As a result of the interaction between the two plasma populations, a modified two-stream instability (MTSI) develops in the mantle region, and waves are excited with frequencies up to a few times the lower hybrid frequency, fLH = (1/2rr)(12ce12cp) •/2 (where Dee and •cp are the gyrofrequencies of electrons and protons, respectively). For the average mantle magnetic field, f/•H is 30-40 Hz. This physical picture was originally proposed by Sagdeev et al. [1990] to explain the wave activity observed in the Martian magnetosphere during the Phobos 2 mission. This paper showed that the excited waves couple the shocked solar wind plasma to the heavy planetary ions, both in energy and momentum, and they also contribute to the large tailward escape of planetary ions observed by the TAUS instrument carried onboard the Phobos 2 spacecraft [Rosenbauer et al., 1989]. Later, noting the similarity between the sheath-ionosphere boundary l...

The Urey organic and oxidant detector consists of a suite of instruments designed to search for several classes of organic molecules in the martian regolith and ascertain whether these compounds were produced by biotic or abiotic processes using chirality measurements. These experiments will also determine the chemical stability of organic molecules within the host regolith based on the presence and chemical reactivity of surface and atmospheric oxidants. Urey has been selected for the Pasteur payload on the European Space Agency's (ESA's) upcoming 2013 ExoMars rover mission. The diverse and effective capabilities of Urey make it an integral part of the payload and will help to achieve a large portion of the mission's primary scientific objective: "to search for signs of past and present life on Mars." This instrument is named in honor of Harold Urey for his seminal contributions to the fields of cosmochemistry and the origin of life.