Sergey Vasilyevich Barabash

The loss of ions from Venus through the plasma wake

Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth’s also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System. Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry, and although the bulk of O and O2 are gravitationally bound, heavy ions have been observed to escape through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.

SERENA: a Novel Instrument Package on board BepiColombo‐MPO to study Neutral and Ionized Particles in the Hermean Environment

SERENA (‘Search for Exospheric Refilling and Emitted Natural Abundances’) is an instrument package that will fly on board the BepiColombo Mercury Planetary Orbiter (MPO); it will investigate the Mercury’s complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge‐exchange processes, and by ionized particles originated through photo‐ionization and again by surface release processes. In order to accomplish the scientific goals, in‐situ analysis of the environmental elements is necessary, and for such a purpose the SERENA instrument shall include four units: two Neutral Particle Analyzers (ELENA and STROFIO) and two Ion Spectrometers (MIPA and PICAM). The scientific merit of SERENA is presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects.