Look at these images of Europa and Ganymede taken with ESO's VLT in Chile! The moons are tiny as seen from Earth, about the size of a 1 Euro coin 3-5 km away. Using adaptive optics we can measure and correct atmospheric turbulence, yielding sharp images like these – the smallest details are only ~150 km! I used to operate this instrument back when I worked at the VLT, and I loved observing Solar System objects like these.

More info: eso.org/public/images/potw2241

Credit: ESO/King & Fletcher