The presented images were obtained using the SPHERE infrared receiver mounted on the ESO’s Very Large Telescope. They demonstrate Ganymede and Europa — two icy moons orbiting Jupiter.
Europa ranks sixth in the list of the largest moons of planets in the Solar System. Its diameter is 3120 km. Thus, it is slightly smaller than our moon. As for Ganymede, it is the largest moon of the planet in the Solar System. Its diameter is 5260 km. This is even larger than the diameter of Mercury.
The orbits of Jupiter’s moons are slightly elliptical — as they orbit the gas giant, they sometimes come closer to it, then move away again. This process leads to their periodic compression and stretching under the influence of the powerful gravitational field of the planet. As a result of the deformations that occur, heat is released, which warms the bowels of the moons and supports the existence of huge oceans in them. It is also believed that most likely, due to tidal influences, active jets and geysers are beating from under the surface of Europa.
Thanks to the new images obtained by SPHERE, as well as spectra, scientists were able to make estimates of chemical compounds on the surfaces of Jupiter’s icy moons. In particular, they found out that the bright areas of Ganymede consist mainly of water, in the form of ice with admixtures of various salts, and that they formed later than the older and darker areas, the composition of which still remains a mystery.
It is worth noting that observing the Jovian moons using ground-based telescopes is not the easiest task. After all, they look like a coin at a distance of 3-5 km — and this despite the fact that the earth’s atmosphere greatly blurs their images. Fortunately, the SPHERE receiver’s adaptive optics system corrects these distortions, providing very clear images in which details as small as 150 km can be seen.
According to https://www.eso.org
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