P34B-01 INVITED
Interaction of a Magnetized Plasma With an Unmagnetized Planet: A Tale of Two Spacecraft
While many spacecraft have explored Venus and its solar wind interaction, much of our understanding is based on the observations from two well instrumented long-lived orbiters. Pioneer Venus has told us much of what we know under solar maximum conditions while Venus Express has provided complementary data at solar minimum. The pressure of the cold ionospheric plasma and its embedded magnetic field stands off the dynamic pressure of the solar wind. At solar maximum the pressure balance point is generally at high altitudes where the plasma is collisionless and the dayside ionosphere stays field-free except when the dynamic pressure is high. At solar minimum the ionospheric pressure stands off the solar wind at lower altitudes where the plasma is collisional. This allows faster diffusion of magnetic field into the ionosphere and it becomes more fully magnetized. Herein, we review our present understanding of the solar wind interaction with Venus based on these observations together with global MHD simulations.
P34B-02 INVITED
Solar Wind Interaction With Mars: From Phobos to MGS, Mars Express, and Beyond
Since 1964 there were only 7 successful / partially successful missions to Mars from 33 attempted carrying instrumentations to study the solar wind interaction. So far there have not been any successful dedicated missions to investigate the near - Mars environment. Nevertheless, earlier American and Soviet missions including Phobos-2 launched in 1988 provided us with basic description of the interaction and helped to formulate detailed scientific objectives for following-on missions. It is MGS and Mars Express launched in 1996 and 2003 respectively that conducted most detailed measurements finding answers to longstanding questions on the Martian magnetic field and dynamic of planetary ions. In this talk I review the MGS and Mars Express results and discuss the outstanding open issues. Those are: dependence of the atmospheric erosion rate on solar / solar wind conditions, mechanisms of planetary ion acceleration and ion extraction from the ionosphere, and effects of magnetic anomalies.
P34B-03 INVITED
Simulated Solar Wind and Kronian Plasma Interactions With Mars and Titan Neutral Environments
Planetary atmospheres are strongly affected by their interaction with solar EUV and incident flowing plasma when atmospheres are not protected by an intrinsic magnetic field. The incident plasma is essentially the solar wind but in some cases it is flowing magnetospheric plasma. This interaction has been investigated by means of three dimensional multispecies hybrid simulation models coupling charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impacts of solar wind (or magnetospheric in Titan's case) electrons, and the charge exchange between the ions and neutral atoms or molecules. This interaction modifies significantly the ionized environment and contributes to the atmospheric erosion. An overview of simulation results, concerning both Mars and Titan plasma environment, are presented. A description of the Martian plasma environment with a uniform Cartesian spatial resolution of ~130 km is given by this simulation model. It reproduces all of the boundaries and regions observed by Mars-Express (MeX) and previous spacecrafts, such as the Bow Shock, the Magnetospheric Boundary, the magnetosheath, the ionosphere,… . In addition, derived applications have been used to estimate the sputtering contribution to the oxygen escape, to estimate the alpha particle capture by the Martian atmosphere and to provide X-ray images of the Martian environment. Another version of this simulation model has been dedicated to investigate the Titan's plasma environment. Results are presented to characterize the main features of the simulated plasma environment of Titan: the induced magnetic tail and the flow of magnetospheric plasma around Titan, as well as the wake and the acceleration of the planetary plasma.
P34B-04 INVITED
Venus Express Contribution to Space Plasma Physics
Venus Express spacecraft (VEX) is magnetically non-clean spacecraft with a small plasma package that consists of FGM magnetometer and plasma instrument ASPERA. System Identification based methodology have been used to separate spacecraft generated interferences and natural signal. The implemented procedure of data cleaning resulted in a high quality magnetic field measurements. VEX FGM contributed not only to many aspects of Venus-Solar Wind interaction but also to fundamental plasma physics problems such physics of collisionless shocks, K-H intability and dynamics of mirror waves. These and other findings of VEX FGM are reviewed.
P34B-05
Comparison of the tail region of Venus and Titan
The Venus Express mission of ESA is exploring the tail formation region of Venus, the Cassini mission flew by Titan along similar orbits that allows to study the tail of Titan. Here we use the data of ASPERA-4 and CAPS charged particles analyzers, the magnetometer data, and the Langmuir probe data of CASSINI, flying onboard of these missions, to compare the tail structure of Venus and Titan. Whereas at Venus the plasma tail exhibits well ordered boundaries below the plasma mantle or its tailward extension (tail boundary, plasma surrounding the current sheet, etc.), at Titan these boundaries are less evident. The common boundary structure is one of the focal issues we study. At Venus the tail is dominated by planetary O+ ions, the ion composition of Titan's tail is more complex. Both at Venus and Titan the origin of the tail might be connected with the nightside ionospheric holes and with a centrifugal acceleration mechanism.
P34B-06
Fine structure of the interface between solar wind and Venusian induced magnetosphere.
At first glance the boundary between the thermalized solar wind flow and Venusian induced magnetosphere seems to be impenetrable for solar wind ions. But the detailed study of the interface region of the planetary wake shows that the structure of such boundary is rather complex. The present work is based on the Venus Express data obtained during 2006 - 2007 time interval. The study was made in coordinate frame referred to the solar wind convection eclectic field. We have distinguished four zones where structure of the interface between solar wind and induced magnetosphere and physical processes defining such a structure are quite different. These zones are located in midnight meridian co-aligned to the convection electric field and in equatorial plane containing IMF and solar wind velocity vectors. We have shown that 1) solar wind plasma can entry into induced magnetosphere in the equatorial region by the mechanism similar to the mechanism of magnetosheath plasma penetration into the Earth magnetosphere via open magnetopause; 2) There is a very strong asymmetry between polar boundary at the positive side of convection electric field ("North") and the opposite side ("South"). "Northern" interface is a very wide region with gradual variation of all parameters and with an essential mixture of the magnetosheath protons and planetary oxygen. The "Southern" indreface is a sharp boundary with a very strong separation of the two (solar wind and magnetosphere) plasma regimes.
P34B-07
Solar Wind Induced mass loss at Mars
Three spacecraft were equipped with ion spectrometers that were able to measure planetary ions loss induced by the solar wind interaction. Mars-5 in 1974 provided the data that suggested importance of this process for evolution of Martian atmosphere. Two plasma instruments on Phobos-2 in 1989 also measured significant outflow of planetary ions that strengthened the case of mass loss problem. However recent Mars- Express results put much lower limit (by about 2 orders of magnitude) to solar wind induced ion escape value. In this presentation comparison of mass loss estimations and measured planetary ion fluxes from different missions and experiments is given in and compared to some theoretical evaluations. Some differences between existing data can be accounted for variations in the solar activity level. Remaining discrepancies, however, are not clearly understood. Forthcoming plasma experiments on Phobos Soil mission can provide additional important data.