Astronomers have unveiled the most stunning and detailed images of two of Jupiter’s largest moons ever taken from Earth’s surface.
The images show the icy surfaces and details of the processes that shape the chemical composition Europe and Ganymedetwo of JupiterThe four Galilean moons of , named after the astronomer who first observed them. And scientists hope that the new images, taken by the Very large telescope (VLT) in Chile, will lay the foundation for future space missions focused on these worlds.
The highly detailed observations reveal geological features on Jupiter’s two frozen moons, including a long, fissure-like mark that slices through Europa’s surface, a type of deformation called a “linae” by planetary scientists.
Related: Juno photos reveal another stunning glimpse of Jupiter’s ice-covered moon Europa
Both the observations of Europa, which are about the size of Earth’s moonand of Ganymede, the largest moon in the solar system and larger than mercury, record the amount of sunlight reflected off the moons’ icy surfaces. This observation produces what astronomers call a reflectance spectrum, which they can then analyze via a process called spectroscopy to reveal the chemical “fingerprints” of specific elements. These reflection spectra allowed scientists to determine the chemical composition of both Jupiter’s moons.
Analysis of Europa showed that its crust consists mostly of frozen water ice with non-ice materials, including a variety of different salts that could not be identified by reflectance spectroscopy, on its surface.
“We mapped the distributions of the various materials on the surface, including the sulphate of frost, which is mainly found on the side of Europa that is most heavily bombarded by the gases around Jupiter,” says team leader and University of Leicester School of Physics and Astronomy Ph.D. Student Oliver King said in a statement. “The modeling indicated that a variety of different salts could be present on the surface, but suggested that infrared spectroscopy alone is generally not able to identify which specific types of salts are present.”
Ganymede’s team’s observations, meanwhile, revealed two types of terrain on the lunar surface. Younger areas were marked by large amounts of water ice than much older regions, composed of a dark gray material that the team has not yet been able to identify.
Shown as blue-colored areas in the VLT image, Ganymede’s icy regions include its polar ice caps and craters, where asteroid impacts have freshly exposed the ice that makes up the Galilean moon’s crust. King and his colleagues also used the images to map the size of ice grains on Ganymede’s surface and to determine how different salts might be distributed on it.
“[The VLT] has allowed us to perform detailed mapping of Europa and Ganymede and observe features on their surfaces smaller than 150 kilometers [90 miles] across – all at distances of more than 600 million kilometers [370 million miles] from Earth,” King said. “Up to now, mapping on this fine scale has only been possible by sending spacecraft to Jupiter to observe the moons up close.”
However, this research does not mean that future missions to these moons are off the table. On the contrary, this mapping of Europa and Ganymede makes the prospect of these spacecraft missions even more enticing.
Creating the conditions for future exploration
Leigh Fletcher led the VLT survey of Europa and Ganymede and is also a member of the science team for ESA’s Jupiter Icy Moons Explorer (JUICE) and NASA’s Europe clippers Mission designed to explore these moons of Jupiter in the early 2030s.
The missions will begin with the launch of JUICE in 2023 to study Europa and Ganymede, as well as a third moon of Jupiter. Callistoas well as the atmosphere and magnetic field of the gas giant.
“These ground-based observations fuel our future exploration of Jupiter’s moons,” Fletcher said. “Planetary missions are subject to severe operational limitations and we simply cannot cover all of the terrain we would like to have, so tough decisions must be made about which areas of the lunar surface deserve the most scrutiny.” These decisions can now include additional context.
NASA’s Europa Clipper mission will follow JUICE to the launch pad in 2024 and focus on determining whether the ocean hiding beneath the moon’s icy surface has life-friendly conditions. Unlike JUICE, Europa Clipper will keep its focus firmly on Europa, analyzing both the inner ocean and the dynamics of the ice tray.
The team’s work is published in two separate papers; the Europe research is detailed in The Planetary Science Journal and the team’s Ganymede findings are discussed in an article accepted for publication in the journal JGR: Planets, currently available on the preprint server ArXiv.
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