Mars – Ion and Neutral Energy Analyser: A new instrumental concept to characterize Mars’ upper atmosphere

The “Mars Magnetosphere ATmosphere Ionosphere and Space-weather SciencE (M-MATISSE)” mission is an ESA Medium class (M7) candidate currently in Phase-A study by ESA. M-MATISSE main scientific goal is to unravel the complex and dynamic couplings of the magnetosphere, ionosphere and thermosphere (MIT coupling) with relation to the Solar Wind (i.e. space weather) and the lower atmosphere of Mars. Among the set of instruments present onboard the platform, the Mars – Ion and Neutral Energy Analyzer (M – INEA) is an energy spectrograph and mass spectrometer specifically designed to image the low energy range of the neutral particles’ energy distribution (<10 eV) with a high energy resolution (~0.1 eV). 

The innovative concept of this instrument consists in the use of an energy analyser capable of instantaneously imaging the energy spectrum of the particles entering the instrument. In addition, a time-of-flight mass analysis is also performed, allowing the mass to be determined simultaneously with its energy. Thanks to an End-to-End model developed with the software SIMION, the performances of the instrument were estimated. The model predicts a resolution in mass of ~22 and in energy better than 0.1 eV as well as a resolution in temperature and velocity better than 50K and 20 m/s respectively. With such capability, M-INEA could, for the first time, provide direct measurement of Mars’ neutral atmospheric escape rate and ultimately bring crucial information to understand the history of the Red Planet Atmosphere. Additionally, with the ability to instantaneously image the energy distribution along the ram direction of the spacecraft, the instrument is also able to measure the temperature and the drift velocity of the particles in the Martian upper atmosphere.

At the same time, we have been working on the development of an ion source, also necessary for the optimal operation of M-INEA, and based on the use of carbon nanotubes (CNT) as electron emitters instead of usual hot filaments. The measured efficiency of this source is comparable to that of sources using hot filaments in mass spectrometers flown on recent space missions, such as ROSINA on Rosetta or NGIMS on MAVEN. Cold emission by CNTs requires much less electrical power than hot filaments and prevents the detrimental instrumental effects due to the outgassing of the heated walls of the ion source and the space charge in high intensity electron beams. The longevity and stability of CNT cathodes are also demonstrated with a test including ∼700 h of continuous emission, showing only a drop of about 20% of the emitted (Steichen et al., 2024).

At present day, the first prototype of M-INEA has been assembled and is being tested at instrumental level. The results obtained during the test campaign will confirm the instrumental concept of M-INEA and give a first estimation of the real performances of the instrument.