Jupiter's jumbo-size moon Ganymede and icy moon Europa posed for the most detailed images ever taken of them from Earth. Planetary scientists from the University of Leicester used the European Southern Observatory's Very Large Telescope in Chile to capture the images and study the moons' surfaces.
You might be staring at these images and thinking "that looks kind of fuzzy," and you'd be right. Compared with what NASA's Juno spacecraft has seen by getting up close to those moons, the Earth-based images look unfocused. But that's OK because this isn't a beauty contest.
The researchers essentially conducted a cosmic fingerprint analysis.
"The new observations recorded the amount of sunlight reflected from Europa and Ganymede's surfaces at different infrared wavelengths, producing a reflectance spectrum," the university said in a statement on Monday. "These reflectance spectra are analyzed by developing a computer model that compares each observed spectrum to spectra of different substances that have been measured in laboratories." This reveals the moons' chemical compositions by matching the reflectance data to known substances such as water and minerals.
The research team published a study on Europa in The Planetary Science Journal earlier this year and has had a study on Ganymede accepted for publication in the journal JGR: Planets.
Jupiter's moons are challenging for Earth-based telescopes because they're far away and relatively small. The VLT's Sphere instrument was able to image the moons in infrared and compensate for distortions caused by our planet's atmosphere. "Mapping at this fine scale was previously only possible by sending spacecraft all the way to Jupiter to observe the moons up close," said planetary scientist Oliver King.
Some interesting details popped out in the data. Ganymede is largely made up of two types of terrain, with young areas consisting of water ice and older areas made up of an as-yet-unknown dark gray material.
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Europa will be the focus of NASA's upcoming Europa Clipper mission. Scientists think the moon is hiding a subsurface liquid ocean and is a good place to look for signs of extraterrestrial life. "We mapped the distributions of the different materials on the surface, including sulphuric acid frost which is mainly found on the side of Europa that is most heavily bombarded by the gases surrounding Jupiter," King said. The moon's crust is mainly made up of water ice.
NASA's Jupiter-studying Juno spacecraft has done close flybys of both moons and delivered stunningly detailed surface views. The new VLT studies show the advantages of using different types of observations to build a more complete picture of what's going on with these mysterious moons.