Though Ganymede is the biggest moon in the solar system — larger in fact than the planet Mercury — and can be seen in the night sky with a simple pair of binoculars, it still appears as just a tiny speck of light next to the much larger Jupiter.
“Ganymede was a fascinating target for me,” said Kardasis, who will present his work at the European Planetary Science Congress in Madrid on Sept. 27, adding that he wanted to go after a very small target in order to test the limits of his abilities.
In order to make the detailed scan, Kardasis, who lives in Athens, Greece, used a fairly modest 11-inch telescope. He attached a video camera to the eyepiece and obtained a series of images, selecting the sharpest frames, about 1,000 total. The best images were stacked together and aligned. Kardasis also processed the photos using imaging software to bring out as much detail as he could.
These techniques produced an albedo map, which records the brightness of different areas on a planet or moon. Kardasis had to time his viewing to take place when conditions were perfect and the atmosphere was fairly calm so as not to blur out Ganymede’s light. In choosing Ganymede, he was helped by the fact that its surface contains highly contrasting light and dark material. Distinguishing between two sources of light right next to each other can be tricky, but the high contrast made it easier to differentiate between areas on the moon’s surface.