NASA’s Juno mission is slated to get close to the solar system’s largest moon, Ganymede, on Monday. This will be the first flyby of the icy world since the Galileo and Cassini spacecraft observed the moon together in 2000. New Horizons also took a quick snapshot of Ganymede as it spun around Jupiter on its way to Pluto in 2007, but from a distance of 3.5 million kilometers. Junos Pass on Monday will come much closer, approaching the surface for 1038 kilometers.
This pass over Ganymede is the first in a series of flybys to the Galilean moons of Jupiter, which together will mark the culmination of Juno’s expanded mission. The probe’s main mission, which began in 2016, focused on the gas giant itself. Juno has taken long, highly elliptical orbits around Jupiter, submerged near the planet to collect data on the planet before moving far above again moves out the planet’s harmful radiation, which threatens the spacecraft’s hardware if left too long.
Ganymede from Galileo’s point of view. Photo credit: Pablo Carlos Budassi (Wikimedia Commons)
Juno will continue to study Jupiter during its expanded mission, but its orbit will now swing it over the previously hidden poles and also help put the planet into context. For example, Juno will conduct the first systematic study of Jupiter’s faint ring system and visit some of its moons.
The scientific goals for the meeting with Ganymede on Monday are far-reaching. Juno will of course use the JunoCam to take photos with visible light, which are not only spectacular to look at, but also allow planetary researchers to observe changes in the surface of Ganymede over time: the photos can be compared to those of Galileo 20 years ago and those of Voyager of . be compared 40 years ago.
Ganymede is the only moon with its own magnetosphere, so Juno’s team is hoping to study it. Dustin Buccino of the Jet Propulsion Laboratory explains, “If Juno flies past Ganymede, radio signals will travel through Ganymede’s ionosphere, causing small frequency changes that should be picked up by two antennas in the Canberra complex of the Deep Space Network in Australia. If we can measure this change, perhaps we could understand the relationship between Ganymede’s ionosphere, its intrinsic magnetic field, and Jupiter’s magnetosphere. “
Juno will also use his microwave radiometer to study Ganymede’s ice crust, which will tell us more about its composition, temperature, and structure.
Ganymede compared to the moon of the earth. Ganymede is 5,268 kilometers wide. Photo credit: Apollo 17 Earth: NASA; Telescope image of the full moon by Gregory H. Revera, computer-aided image by Ganymede: NASA / JPL / DLR.
Ganymede is a fascinating world. Since it is larger than Mercury, it would be classified as a planet if it orbited the Sun instead of Jupiter. It’s also fascinating because it’s a water world, with liquid oceans beneath its surface. This makes it one of the solar system’s best candidates for microbial alien life. On the other hand, Ganymede’s ocean may not be in contact with rocks at its bottom, but instead is trapped between two layers of ice sheets. On earth, the chemical reactions caused by water in contact with rocks provide energy for some types of microbes – if Ganymede’s ocean lacks this key ingredient, it may be sterile, but the jury has yet to decide.
However, it is expected that there is contact of liquid water and rock on another moon of Jupiter: Europe. In the coming years, Juno will also visit Europe more than once. Juno’s expanded mission will also take a closer look at Io, the fiery innermost moon of Jupiter, a place that is more volcanically active than anywhere else in the solar system. We can expect some stunning imagery and new scientific knowledge from these upcoming flybys. The observations made by Juno will complement and prepare the stage for two upcoming missions to the moons of Jupiter. The European Space Agency’s JUICE will launch in 2022 and will take a closer look at Ganymede, Callisto and Europe. NASA’s Europa Clipper will follow later in the 2020s.
Learn more: “NASA’s Juno for an up-close look at Jupiter’s moon Ganymede,” JPL.
Featured Image: Ganymede Mosaic and Geological Map by Voyager and Galileo Data. Photo credit: USGS Astrogeology Science Center / Wheaton / NASA / JPL-Caltech.