Towards in situ measurements of the chemical composition of Earth’s lower thermosphere

The chemical composition of Earth's lower thermosphere around an altitude of 180 km remains a largely uncharted territory. This altitude marks a critical transition region, where the atmosphere shifts from being dense and collision-dominated to a regime of free molecular flow. In this region, the altitude profiles of the present chemical species demonstrate their steepest gradients, a phenomenon crucial for understanding the dynamic interplay between the lower thermosphere and the mesosphere. Despite its importance, this region remains poorly explored due to limited in situ observations. Our focus is on the deployment of a highly miniaturized mass spectrometer, specifically designed for a CubeSat platform where it will be accommodated within 1U. This advanced instrumentation is designed to measure in situ all species present in this part of the atmosphere. Thanks to its novel ion source design, it is capable of measuring atoms, molecules, radicals, and isotopes, with exceptional sensitivity, dynamic range, mass range, and mass resolution even at the hyper-velocities of spacecraft during these measurements. The core of our discussion revolves around the expected data quality and performance capabilities of this mass spectrometer, particularly its operation at the perigee in the lower thermosphere. The data obtained from this innovative approach are expected to shed light on the complex dynamics at play in this scarcely studied region. We anticipate that these findings will significantly contribute to the scientific community’s understanding of the lower thermosphere, its coupling with the mesosphere, and the exosphere, filling a crucial gap in our current knowledge and potentially paving the way for future research in both atmospheric science and comparative planetology.