This false color view from the JWST’s NIRCam instrument’s 2.12 micron filter shows the distinct bands that encircle Jupiter and the planet’s Great Red Spot. The iconic spot appears white in this image because of the way the infrared image was processed. The moon Europa is visible on the left, and its shadow can be seen to the left of the Great Red Spot.
The New Horizons spacecraft flew by Jupiter for a gravity assist maneuver on its way to Pluto and the Kuiper Belt. It took this picture of the moon Europa rising above Jupiter’s clouds just after its closest approach to the planet.
On 24 January, the Hubble Space Telescope captured the rare occurrence of three of Jupiter’s largest moons moving across the face of the gas-giant planet: Europa, Callisto, and Io.
They are three of the four Galilean moons, named after the 17th-century scientist Galileo Galilei who discovered them with a small telescope. Their orbital periods around Jupiter range from 2 days to 17 days. The Galilean moons can often be seen transiting the face of Jupiter and casting shadows onto its cloud tops., but seeing three of them transiting the face of Jupiter at the same time is rare, occurring only once every five or ten years.
On the left, the moons Callisto and Io are above Jupiter’s cloud tops. The shadows from Europa, Callisto, and Io are strung out from left to right. Europa is not visible in this image. Approximately 42 minutes later (right-side image), Europa has entered the frame at lower left. Slower-moving Callisto is above and to the right of Europa. Fastest-moving Io is approaching the eastern limb of the planet; its shadow is no longer visible on Jupiter. Europa’s shadow is toward the left side of the image, and Callisto’s shadow to the right. The moons’ orbital velocities are proportionally slower with increasing distance from the planet. Ganymede, the other Galilean moon, was outside Hubble‘s field of view and too far from Jupiter to be part of this conjunction.
Each of these moons has a distinctive color. The cratered surface of Callisto is brown; the smooth icy surface of Europa is yellow-white; and the volcanic, sulfur-dioxide surface of Io is orange. The fuzziness of each depends on each moon’s distance from Jupiter. The farther away the moon, the softer the shadow because it is more spread out across the disk.
Jupiter’s icy moon Europa is crisscrossed with rifts in its surface. Agenor Linea is an unusually bright, white band on Europa. The mosaic of color images above yields a high resolution view of Agenor within lower resolution images of the surrounding area. The images were captured by the Galileo spacecraft in 1998 and have been used by planetary scientists and astronomers to try to understand the “geology” of Europa.