Europa & Ganymede: The Icy Moons of Jupiter | ESO

Europa & Ganymede: The Icy Moons of Jupiter | ESO

This image shows a black and white image of Jupiter. In front of the giant planet in a plane are images of its icy moons Europa and Ganymede. These images show the moons in beige, like sand, and blue, with darker and brighter regions. Below the planet there are larger images of the moons, with timestamps that indicate these images being captured on different days, revealing different sides of the moons.

This image shows two of Jupiter’s moons, the icy Ganymede and Europa, which have been imaged in the infrared using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope (VLT). Whilst Europa is quite similar in size to our own Moon, Ganymede is the largest moon in the whole Solar System—it is even bigger than the planet Mercury! 

Their orbits around Jupiter are slightly elliptical, so they get closer and further away from the planet as they orbit it. This results in the moons being stretched and squeezed by the gravitational pull from Jupiter at periodical intervals. This creates frictional heat, warming the insides of the moons, which has made them geologically active. Europa in particular is likely to have active plumes and geysers erupting from the oceans of liquid water beneath the thick ice cover that makes up the surface. 

Estimates on the abundances of chemical species on the marble-like surfaces of these moons could be made thanks to these new images and also spectra, which have been published in two studies by Oliver King and Leigh N. Fletcher at the University of Leicester in the United Kingdom. They found that the bright regions of Ganymede consist mainly of water in the form of ice with hints of various salts, and that they have formed more recently than the older darker patches, whose composition still remains a mystery to astronomers.

Observing these moons with ground-based telescopes is challenging, because they look as small as a 1 Euro coin seen from 3-5 km away. Earth’s atmosphere would completely blur these images, but SPHERE’s adaptive optics system corrects these distortions, delivering very sharp images with details as small as 150 km.

Credit: European Southern Observatory (ESO)/King & Fletcher. Jupiter background image: NASA, European Space Agency (ESA), A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.

Release Date: October 10, 2022

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