MAJIS 2024 Earth Gravity Assist data: comparison with PRISMA and lightning storm spectroscopic detection

On the 20^th of August 2024 the JUpiter ICy moons Explorer spacecraft (JUICE, Grasset et al., 2013) performed a Lunar-Earth Gravity Assist (LEGA), allowing for a first check of scientific performances on planetary targets. In this study we present the analysis performed on data acquired by the Moon and Jupiter Imaging Spectrometer (MAJIS, covering in two channels the spectral range 500-5500 nm with spectral resolution of the order of 5-7 nm and spatial resolution up to 1 km/pixel in Earth observations, Poulet et al., 2024) during the Earth Gravity Assist alone (EGA).

With the purpose of validating MAJIS functioning, we compared its multispectral images of Earth surface (targeting the Western Pacific Ocean at tropical latitudes) with similar visual/near-infrared (VIS/NIR) acquisitions from the Earth-orbiting PRISMA imaging spectrometer, managed by the Italian Space Agency. Covering mostly ocean and cloudy features, this investigation has been focused on preliminarily characterizing several terrestrial atmospheric properties, including composition, temperature and high altitude structures. In particular, the widespread presence of H₂O ice in high altitude clouds allowed characterizing its properties (e.g., abundance, crystals’ size, crystallinity) through different spectral signatures at NIR and thermal wavelengths. This provides a first benchmark to this observable in view of Jupiter’s icy satellites investigation by Juice. Very few land features could be identified through thermal contrast with the surrounding ocean. Moreover, high altitude gravity waves were detected through the mapping of the 4300 nm CO₂ emission.

Another interesting finding involves the first space-based spectroscopic detection of lightning in a planetary atmosphere. Four flashes were identified by MAJIS during the night, in proximity of optically thick clouds offshore of Sumatra island. Although simultaneous detections from ground networks of lightning sensors are missing, evidence for this unambiguous interpretation of the event is provided by diagnostic emission lines of atomic oxygen and nitrogen in the VIS/NIR range, typical of lightning. While MAJIS is not optimized for similar serendipitous observations, we could evaluate the total optical emitted energy, and estimate the temperature of the lightning channel, even if under quite strong assumptions on the involved spectral, spatial and temporal resolutions. Such an analysis provides a basis for the ongoing planning of lightning search with MAJIS at Jupiter, with focus on the H I emissions near 650 and 1870 nm.

References

Grasset, O.,  et al., 2013. JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system. Planetary and Space Science, 78, pp. 1–21. https://doi.org/10.1016/j.pss.2012.12.002

Poulet, F.,  et al., 2024. Moons and Jupiter Imaging Spectrometer (MAJIS) on Jupiter Icy Moons Explorer (JUICE). Space Science Reviews 220, 27. https://doi.org/10.1007/s11214-024-01057-2

Acknowledgements

JUICE is a mission under ESA leadership with contributions from its Member States, NASA, JAXA and the Israel Space Agency. It is the first Large-class mission in ESA’s Cosmic Vision programme. This work was supported by CNES, focused on MAJIS. This work has been developed under the ASI-INAF agreement no. 2023-6-HH.0.

The MAJIS data acquired during the JUICE Moon–Earth flyby in August 2024 are currently under the mission’s cruise-phase proprietary period. These data will be made available through the ESA Planetary Science Archive following the first Cruise Archive Delivery, which is currently scheduled for six months after Earth Gravity Assist #3 in 2029.

PRISMA products are generated by IAPS-INAF under a license from ASI Original PRISMA Product - © Italian Space Agency (ASI) – 2024. ASI retains copyright on the ORIGINAL Product “PRISMA Product - © Italian Space Agency (ASI) 2024. All rights reserved“.