VISTA: a micro-thermogravimeter to analyze condensable species in planetary atmospheres

Thermogravimetry is a technique largely used in order to study absorption/desorption and sublimation/evaporation processes in several environments. Micro-thermogravimetry (mu-TGA) is particularly suitable for space applications, due to the very small mass, volume and power required by mu-TGA sensors. VISTA (Volatile In Situ Thermogravimetry Analyser) is a micro-thermogravimeter developed at IAPS-INAF (Rome) which aims to measure the amount of volatiles of scientific interest (e.g. water, organics) in planetary environments. It is based on Piezoelectric Crystal Microbalances (PCM), whose resonant frequency is linearly related to the deposited mass. The PCM heating/cooling allows the release/deposition of volatile materials, allowing to measure their abundance and to infer their composition. The instrument has been selected in the payload of the ESA MarcoPolo-R proposed mission, aiming to analyze in situ and bring to Earth samples of asteroidal regolith. In this framework, VISTA would measure the water and organic content in the asteroid regolith, detect the possible cometary-like activity of the asteroid and assess the contamination issue. VISTA could be used also to assess relevant scientific issue concerning planetary atmospheres. It has been studied for the ESA Cosmic Vision proposed missions EVE (European Venus Explorer) and TAE (Titan Aerial Explorer), which planned an in-situ analysis of the Venus and Titan atmosphere, respectively. In the framework of a Venus in-situ mission, VISTA would have the following goals: - Measurement of dew points of condensable species, and hence of humidity (by cooling the PCM down to condensation temperatures) - Measurement of amount of refractory species in the Venus cloud aerosols (by heating the PCM) - Measurement of electric charge of cloud particles (by coupling the thermogravimeter and an electric field generator) In the framework of a Titan in-situ mission, the heating of the VISTA PCM would: - determine the presence of nucleating aerosols in cloud droplets, hence whether methane cloud droplets homogeneously or heterogeneously nucleate - measure the abundance of organic compounds of particular scientific interest present as nucleating seeds within cloud particles (acetylene, benzene, HCN)