The last time we saw Jupiter’s largest moon Ganymede up close was over two decades ago. Now, NASA has released new close-ups of the moon, taken on June 7, 2021 by Juno orbits. The stunning images reveal Ganymede’s icy surface in striking detail. They show the craters of the moon, light and dark terrain and long linear features that may resemble tectonic faults on Earth.
First flyby of Ganymede in over 20 years
This is the closest that any spacecraft has come to the giant moon since the Galileo spacecraft closed close on May 20, 2000. Juno flew past Ganymede’s Monday, June 7 at 13:35 EDT (10:35 PDT). It came within 1,038 km of the surface at the nearest approach. Scott Bolton of the Southwest Research Institute (SwRI) and the Juno Principal Investigator said in a statement:
This is the closest any spacecraft has come to this mammoth moon in a generation. We will take our time before drawing any scientific conclusions, but until then we can simply marvel at this heavenly wonder.
New images of Ganymede and its icy surface
The pictures give our first good glimpse of this mysterious world in over two decades. One image was taken by Juno’s JunoCam imaging, and the other is from the Stellar Reference Unit (SRU).
Juno was able to capture almost an entire page of Ganymede with JunoCam with a resolution of 1 km per. Pixel. Right now, most photos are in black and white, but other pending photos will be in color.
The SRU camera looked at Ganymede’s dark side, illuminated only by dim sunlight reflecting from Jupiter. The resolution in the image is 0.37 to 0.56 miles (600 to 900 meters) per second. Pixel. According to Heidi Becker, Juno’s radiation monitoring at JPL leads:
The conditions in which we gathered the dark side image of Ganymede were ideal for a low-light camera like our Stellar Reference Unit. So this is a different part of the surface than seen by JunoCam in direct sunlight. It will be fun to see what the two teams can put together.
Juno, Jupiter and Ganymede
Juno’s primary mission has been to study Jupiter itself and examine its clouds, storms, and deep interiors. But the spacecraft is also well-equipped to look at some of its moons. As Bolton explained:
Juno carries a range of sensitive instruments that can see Ganymede in ways never before possible. By flying so close, we bring the exploration of Ganymede into the 21st century, both complementing future missions with our unique sensors and helping prepare the next generation of missions for the Jovian system: NASA’s Europa Clipper and ESA ‘is [European Space Agency’s] JUpiter ICy Moon Explorer [JUICE] mission.
The probe also used other instruments to study Ganymede, including Ultraviolet Spectrograph (UVS) and Jovian Infrared Auroral Mapper (JIRAM). The Microwave Radiometer (MWR) instrument can also better determine the composition and temperature of Ganymede’s water ice crust.
Largest moon in the solar system
Ganymede is not only Jupiter’s largest moon, it is the largest natural satellite in the entire solar system. It is even larger than the planet Mercury. It is also the only moon that has its own magnetosphere. A magnetosphere is a bubble-shaped region of charged particles around a body such as a planet or moon.
Like Jupiter’s other large moons Callisto and Europe, Ganymede’s has an icy surface and outer shell. This surface has craters, unusual light and dark areas and long cracks similar to tectonic faults on Earth. These are signs of active geology on the moon in the past and perhaps still in progress. Bolton said:
Ganymede’s ice shell has some light and dark areas, suggesting that some areas may be pure ice, while other areas contain dirty ice. The MWR will provide the first in-depth study of how the composition and structure of ice varies with depth, leading to a better understanding of how ice shells are formed and the ongoing processes that resurface ice over time.
An ocean on Ganymede?
Ganymede has three main layers: a metallic iron core, a rocky mantle, and an outer shell of ice about 800 miles (800 km) thick. In 2015, NASA’s Hubble Space Telescope also found evidence of an underwater ocean at Ganymede. The ocean beneath the ice crust is estimated to be 100 miles deep, 10 times deeper than Earth’s garden. John Grunsfeld, former associate administrator of NASA’s Science Mission Directorate, said:
This discovery marks an important milestone and highlights what only Hubble can accomplish. In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep sea beneath Ganymede’s icy cold opens up further exciting possibilities for life beyond Earth.
If confirmed, Ganymede’s ocean would be one of several now known to exist on icy moons in the outer solar system. Europe and Enceladus are the two most famous of these worlds. Could it be habitable? No one knows yet until more data is obtained.
Juno will be sending more photos back from flyby in the coming days, so stay tuned! Raw images are available on the JunoCam website.
The spacecraft has orbited Jupiter since 2016 and has studied the giant planet’s deep atmosphere, clouds, storms, northern lights and hidden interiors. It has also previously taken some beautiful pictures of active volcanoes on the moon Io.
Bottom line: NASA’s Juno spacecraft has sent the first new close-up of Jupiter’s largest moon Ganymede back in over 20 years.