NASA has authorized an extension of the mission to its Juno spacecraft exploring Jupiter. The agency’s most distant planetary orbiter will now continue its investigation of the largest planet in the solar system until September 2025, or until the end of the spacecraft’s life. This expansion requires Juno to become an explorer of the entire Jovian system – Jupiter and its rings and moons – with multiple encounters planned for three of Jupiter’s most intriguing Galilean moons: Ganymede, Europe, and Io.
“Since its first orbit in 2016, Juno has made one revelation after another about the inner workings of this gas giant,” said lead researcher Scott Bolton of the Southwest Research Institute in San Antonio. “With the expansion of the mission, we will answer fundamental questions that arose during Juno’s main mission, as we sailed past the planet to explore Jupiter’s annular system and the Galilean satellites.”
Proposed in 2003 and launched in 2011, Juno arrived in Jupiter on July 4, 2016. The main mission will end in July 2021. The extended mission involves 42 additional orbits, including passages near the polar cyclones of northern Jupiter; overflights of Ganymède, Europa and Io; as well as the first in-depth exploration of the weak rings that surround the planet.
“By expanding the scientific objectives of this important orbital observatory, the Juno team will begin to address a range of science historically required from flag ships,” said Lori Glaze, director of the planetary science division at NASA Headquarters at Washington. “This represents an effective and innovative breakthrough for NASA’s solar system exploration strategy.”
The data Juno collects will contribute to the goals of the next generation of missions for NASA’s Jovian – Europa Clipper system and ESA’s European Space Agency mission JUpiter ICy Luons Explorer (JUICE). Juno’s investigation of Jupiter’s volcanic moon, Io, addresses many of the science goals identified by the National Academy of Sciences for a future Io exploratory mission.
The expanded mission’s science campaigns will expand on the discoveries Juno has already made about Jupiter’s internal structure, internal magnetic field, atmosphere (including polar cyclones, deep atmosphere, and aurorae), and magnetosphere.
“With this expansion, Juno becomes its own subsequent mission,” said Steve Levin, a Project Juno scientist at NASA’s Jet Propulsion Laboratory in Southern California. “Near pole observations, radio masking” – a remote sensing technique for measuring the properties of a planetary atmosphere or ring systems – “focused satellite flights and magnetic field studies combine to make one new mission, the next logical step in our exploration of the Jupiter system. ”
Juno maps the cold waters of northern Ganymede
Infrared observations of instruments in the Juno spacecraft cover regions of Ganymede not visible to ground-based telescopes.
Jupiter’s moon, Ganymede, is the largest planetary satellite in the solar system. It’s also one of the most intriguing: Ganymede is the only moon with its own magnetic field, is the most distinctive of all moons, and likely has an underground ocean of liquid water. It was studied by the first flights of Jupiter by the Pioneer and Voyager spacecraft, but our understanding today is largely based on observations made by NASA’s Galileo orbiter from 1995 to 2003.
Mura et al. now reports some of the first in situ observations of Ganymede since the end of the Galileo mission. They used the Jovian Infrared Auroral Mapper (JIRAM) aboard NASA’s Juno spacecraft to obtain images and spectra of the moon’s north polar region. On December 26, 2019, Juno passed Ganymede at a distance of approximately 100,000 kilometers, allowing JIRAM to map this region with a spatial resolution of up to 23 kilometers per pixel.
As Juno flies through Ganymede, the spacecraft can observe physical locations on the moon’s surface from different angles. By comparing the brightness of these regions in a range of viewing and lighting geometries, the authors developed a photometric model for the reflectance of the Ganymede surface. They observed that wavelength-dependent reflectance ratios sometimes break near relatively new craters, possibly due to a larger average ice grain size in these regions.
Combining their model with spectral observations of the 2 micron water ice absorption band allowed the authors to map the distribution of water ice in the North Polar region. Where these estimates coincided with maps derived from telescoping Earth-based observations, the researchers found an overall satisfactory agreement. This congruence allowed them to extend the global map of the Ganymede water ice to latitudes much further north.
Observations in other spectral bands also revealed the presence of non-aquatic chemical species on Ganymede’s surface, including possible detections of hydrated magnesium salts, ammonia, carbon dioxide, and various organic molecules. The authors note that 2020 offered Juno additional opportunities to make polar observations of Ganymede, as well as in 2021, and suggest that JIRAM’s continued observations will help define observation strategies in future observation campaigns, such as the Europa Clipper and Jupiter Icy Moons Explorer missions. (JUICE).