JUICE-MAJIS Earth observations during the 2024 gravity assist: first analysis and comparison with PRISMA data

Abstract. The JUpiter ICy moons Explorer spacecraft (JUICE) performed a Lunar-Earth gravity assist maneuver on 20th August 2024, during which the scientific instruments were turned on to test their functionality. At the Earth, the Moon and Jupiter Imaging Spectrometer (MAJIS) acquired a sequence of multispectral images over the Western Pacific Ocean at tropical latitudes. In parallel, an observing campaign was also conducted by the Earth-orbiting PRISMA imaging spectrometer, with the purpose of validating MAJIS spectral observations with independent measurements of the same kind.

These two datasets are here exploited to investigate and compare several atmospheric and cloud properties, including composition, temperatures, and atmospheric gravity waves. In the MAJIS spectral range, covering the 500–5560 nm wavelengths, we identified major and minor atmospheric gases, including O₂, H₂O, CO₂, O₃, CH₄, N₂O. Since MAJIS observations mostly covered diffuse cloudiness over the ocean, our analysis mainly focused on the discrimination of clouds’ properties and altitudes. We verified that ice particles are widespread in the data, allowing for an investigation of their properties (e.g. crystallinity) through different spectral signatures. The only land features identified in MAJIS data are not observed in daylight, hence only a thermal emission analysis is presented. Finally, the coverage of the 4300 nm CO₂ band enables the identification of high altitude structures, revealing the presence of several atmospheric wave packets, likely induced by convective events, or lightning strikes known to have occurred at the time of the flyby. The present analysis demonstrates how MAJIS data can contribute to the scientific investigation of an atmospheric environment, and provide the first benchmark in the analysis of water ice, whose characterization in the Jovian system will be of primary importance for the JUICE mission.