Chemical and Isotopic Composition Measurements on Atmospheric Probes Exploring Uranus and Neptune

Abstract

So far no designated mission to either of the two ice giants, Uranus and Neptune, exists. Almost all of our gathered information on these planets comes from remote sensing. In recent years, NASA and ESA have started planning for future mission to Uranus and Neptune, with both agencies focusing their attention on orbiters and atmospheric probes. Whereas information provided by remote sensing is undoubtedly highly valuable, remote sensing of planetary atmospheres also presents some shortcomings, most of which can be overcome by mass spectrometers. In most studies presented to date a mass spectrometer experiment is thus a favored science instrument for in situ composition measurements on an atmospheric probe. Mass spectrometric measurements can provide unique scientific data, i.e., sensitive and quantitative measurements of the chemical composition of the atmosphere, including isotopic, elemental, and molecular abundances. In this review paper we present the technical aspects of mass spectrometry relevant to atmospheric probes. This includes the individual components that make up mass spectrometers and possible implementation choices for each of these components. We then give an overview of mass spectrometers that were sent to space with the intent of probing planetary atmospheres, and discuss three instruments, the heritage of which is especially relevant to Uranus and Neptune probes, in detail. The main part of this paper presents the current state-of-art in mass spectrometry intended for atmospheric probe. Finally, we present a possible descent

Advances in Mass Spectrometers for Flyby Space Missions for the Analysis of Biosignatures and Other Complex Molecules

“…To increase the mass resolution, the Mass Spectrometer for Planetary Exploration (MASPEX) instrument on board Europa Clipper makes use of the multi-bounce technique [37,53]. Details on the comparison and use case of MASPEX-type and NIM-type instruments are described in reference [11]. Species bounce multiple times between two ion mirrors before they are registered, which significantly increases their time-of-flight.…”

“…Regarding the complexity of molecules to be analyzed, two major groups of questions can be identified: on the one hand, fundamental questions on the origin and evolution of many Solar System objects can be revealed by analyzing atomic gas and simple molecules present in the exosphere [10]. Many of those species are known or at least expected to be present in various exospheres to at least some extent including CH 4 , CO, NH 3 , N 2 ; the noble gasses up to Xe and the isotopic ratios D/H, 3 He/ 4 He, 13 C/ 12 C, 15 N/ 14 N, 20 Ne/ 22 Ne, 38 Ar/ 36 Ar, 2 of 18 36 Ar/ 40 Ar, as well as those of Kr and Xe, e.g., [11][12][13][14][15] and references. The named species cover a mass range of about m/z 1 to 135, where m/z is the mass-to-charge ratio.…”

“…Mass spectrometry is a proven technique for the in situ investigation of chemical compositions of gaseous and solid samples [11,35,36]. The analysis of solid samples demands for impact ionization mass spectrometers, e.g., [30].…”