[1] Measurements conducted with the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) instrument of the Mars Express spacecraft provide data of plasma fluxes that stream away from the polar regions of the Mars ionosphere with energy spectra whose peak value increases with distance from the planetary surface. The observed energy distribution reveals a velocity boundary layer with ionospheric plasma that is eroded from the polar regions of the Mars ionosphere and that extends in the downstream direction within a geometry similar to that present along the polar flanks of the Venus ionosheath. The direction of motion of the ionospheric particles in those fluxes is close to that of the solar wind velocity and is not also oriented in a transverse direction as would have been expected if they were solely accelerated by the convective electric field of the solar wind. The ionospheric plasma eroded and deviated by the solar wind within the boundary layer forms a region whose shape is compatible with that of the asymmetric Mars plasma halo that was inferred from the X-ray emission lines measured with the reflecting grating spectrometer of the XMM-Newton telescope. The latter emission is interpreted as resulting from thermal dissipative processes associated with the transport of solar wind momentum to the polar upper ionosphere where both plasma populations interact with each other. Different conditions are applicable throughout most of the dayside hemisphere where the enhanced interplanetary magnetic field intensities that are observed within the ionosphere should make the interaction of the oncoming solar wind plasma with the ionospheric material less efficient.

No abstract

The planets magnetic field has been explained based on the dynamo theory, which presents as many difficulties in mathematical terms as well as in predictions. It proves to be extremely difficult to calculate the dipolar magnetic moment of the extrasolar planets using the dynamo theory. The aim is to find an empirical relationship (justifying using first principles) between the planetary magnetic moment, the mass of the planet, its rotation period and the electrical conductivity of its most conductive layer. Then this is applied to Hot Jupiters. Using all the magnetic planetary bodies of the solar system and tracing a graph of the dipolar magnetic moment versus body mass parameter, the rotation period and electrical conductivity of the internal conductive layer is obtained. An empirical, functional relation was constructed, which was adjusted to a power law curve in order to fit the data. Once this empirical relation has been defined, it is theoretically justified and applied to the calculation of the dipolar magnetic moment of the extra solar planets known as Hot Jupiters. Almost all data calculated is interpolated, bestowing confidence in terms of their validity. The value for the dipolar magnetic moment, obtained for the exoplanet Osiris (HD209458b), helps understand the way in which the atmosphere of a planet with an intense magnetic field can be eroded by stellar wind. The relationship observed also helps understand why Venus and Mars do not present any magnetic field.

[1] Measurements conducted with the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) instrument in the Venus Express spacecraft reveal the presence of a plasma transition within a boundary layer that extends along at the flanks of the Venus ionosheath and where the solar wind exhibits changes similar to those reported from previous missions (Mariner 5, Venera, and Pioneer Venus). At the plasma transition there is a sharp downstream decrease in the density of the solar wind electrons and a sudden increase in their temperature embedded within the boundary layer where more gradual changes in the speed, temperature, and density of the solar wind ions are observed. The ASPERA-4 data also show important fluxes of planetary ions measured downstream from the plasma transition and whose dominant velocity component is in the Sun-Venus direction. The speed of those ions is slower than the local solar wind speed and thus is different from that expected from the convective electric field acceleration in which both speed values should be comparable. The boundary layer is interpreted as representing a feature that results from the transport of solar wind momentum to the Venus upper ionosphere, and the ASPERA-4 data provide information on the kinetic properties of the eroded planetary ion population that is seen to stream mostly in the Sun-Venus direction. From the comparison of the ASPERA-4 measurements with those of the magnetic field obtained with the magnetometer of the Venus Express, it is found that in the near wake crossing of the plasma transition the magnetic field intensity decreases to lower values with downstream distance from the planet in agreement with measurements conducted with the Mariner 5 and the PVO. From the analysis of data for orbits with evidence of the plasma transition within the boundary layer, it is found that the momentum flux of planetary ions measured in the wake can be accounted for from the incident momentum flux of the solar wind protons implying an approximate balance as would result from the transport of solar wind momentum to the planetary particles.

[1] Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O + ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure, and as a result, those ions are not solely being driven by magnetic forces but also by the kinetic energy of the solar wind. Beams of planetary O + ions with those properties have been detected in several orbits of the Venus Express through the Venus wake as the spacecraft traverses by the noon-midnight plane along its near-polar trajectory. The momentum flux of the O + ions leads to superalfvenic flow conditions. It is suggested that such O + ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions. The distribution of the number of cases where superalfvenic and subalfvenic conditions are measured along the Venus Express trajectory leads to dominant values when the total kinetic plasma pressure (including that of the solar wind protons) and the magnetic pressure are comparable, thus suggesting a possible equipartition of energy between the plasma and the magnetic field.