Jupiter’s moon is the largest planetary satellite in the Ganymede solar system. It is also one of the most intriguing: Ganymede is the only moon with its own magnetic field, it is the most isolated of all moons, and it is probably near a subsurface ocean of liquid water. It was studied by early Jupiter flybys made by the Pioneer and Vyjar spacecraft, but our understanding today largely rests on observations made from 1995 to 2003 by NASA’s Galileo Orbiter.
Mura et al. Now report some of the in-situ observations of Ganymede since the end of the Galileo mission. He used the Jovian Infrared Auroral Mapper (JIRAM) on NASA’s Juno spacecraft to take images and spectra of the lunar north polar region. On 26 December 2019, Juno passed Ganymede at a distance of approximately 100,000 kilometers, enabling JIRAM to map the region at spatial resolution of up to 23 kilometers per pixel.
As Juno flies over Ganymede, the spacecraft can observe physical locations on the lunar surface from a wide variety of angles. Comparing the brightness of these regions to a range of observations and illumination geometry, the authors developed a photometric model for Ganymede’s surface reflectance. They observed that the wavelength-reflective reflection relationship sometimes broke in the area around relatively fresh craters, probably due to the large size of the ice grains in these areas.
Mixing their model with spectral observations of the 2-micrometer water ice absorption band allowed the authors to map the distribution of water ice in the North Polar region. Where these estimates overlapped with maps obtained from Earth-based telescopic observations, the researchers largely found good agreement. This congratulation enabled him to expand the global water ice map for Ganymede to no greater latitudes.
Observations in other spectral bands also detected the presence of non-water chemical species on the surface of ganymedes, including the potential inhibition of a series of hydrated magnesium salts, ammonia, carbon dioxide, and organic molecules.
NASA takes first images of Juno Joan’s moon Ganymede’s North Pole
a. Mura et al. Ganymede’s infrared observation from Jovian Infrared Aroel Mapper on Juno, Journal of Geophysical Research: Planets (2020). DOI: 10.1029 / 2020JE006508
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Quotes: Juno retrieved water ice in northern Ganymede (2021, 21 January) from https://phys.org/news/2021-01-juno-ice-norministr-ganymede.html on 21 January 2021.
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