© NASA / SwRI / MSSS / Io image (detail)
Volcanic moon Io on February 3, 2024 | The Juno space probe captured this image of Jupiter’s moon Io from a distance of 3,850 kilometers. The night side is illuminated by Jupiter, so that the entire hemisphere of the celestial body can be seen. The smallest visible details are about a kilometer in size. Numerous volcanoes appear as dark spots and a multitude of towering mountains.
It is also interesting why you can see structures on the night side of Io: This side of the moon is illuminated so strongly by the bright surface of the mother planet Jupiter that the JunoCam makes it possible to also make the night side visible, which is illuminated by Jupiter . Below the center of the crescent, which is directly illuminated by the sun, is the Ra Patera volcano, which was photographed by the two Voyager space probes during their flyby in 1979. It is surrounded by numerous bright lava flows that spread over several hundred kilometers in almost all directions. A high mountain range rises immediately next to it.
A D-shaped structure can be seen diagonally above Ra Patera. It is the Loki Patera volcano with a solidified lava lake. It appears pitch black in most pictures, but here it appears shiny. Apparently it has a very smooth surface that reflects sunlight well. Loki Patera was also discovered by the Voyager spacecraft, at which time it was belching gas and lava. It currently appears to be dormant, but it can become active again at any time.
The extreme volcanic activity on Io, which at 3,643 kilometers in diameter is only slightly larger than our moon, is due to the enormous tides caused by Jupiter. Like most large moons, Io rotates in a locked manner, meaning it always faces Jupiter on the same side. This means that the tidal mountains on Io, which are up to 500 meters high, should have solidified long ago. But the neighboring moons Europa and Ganymede, which orbit Jupiter at an integer multiple of Io’s orbital period, periodically deflect the moon from its resting position, so that the tidal ridges on Io move back and forth somewhat. This results in extremely strong friction in the silicate shell of Io, which is largely melted. In the case of Io, the idea of a glowing interior is correct, while the rocky mantle of our Earth consists of around 98 percent solid rock.