We have just had our closest look at Jupiter’s volcanic moon Io for decades, thanks to NASA’s Juno spacecraft, which passed the moon on 30 December.
Juno, which has been orbiting Jupiter since 2016, has been taking increasingly close images of Io in recent months as its path around Jupiter changes.
This latest image was taken just 1500 kilometres above the moon’s surface. In it, some of Io’s hundreds of towering mountains are visible, which can reach more than 10 kilometres tall, as well as their long, sharp shadows.
Io is thought to be the most volcanically active body in the solar system and has hundreds of active volcanoes. These volcanoes tend to be smaller than the largest mountains, averaging only 1 or 2 kilometres in height, and are harder to make out in the image.
However, by comparing images and data from Juno’s previous 56 flybys of the moon, astronomers can learn about how these volcanoes have varied over time and why they are so active.
Juno has also been investigating Jupiter’s other moons, including Europa and Ganymede, collecting data and taking the closest images since NASA’s Galileo orbiter visited the area in 2001. In February, Juno will make another extremely close flyby, again at around 1500 kilometres above Io’s surface.
Juno is scheduled to de-orbit into Jupiter towards the end of 2025, after flying by Io a further seven times, but that won’t be the end of our learning about Jupiter’s moons. NASA’s Europa Clipper spacecraft, which is set to launch in October this year, is designed to zip just 25 kilometres above Europa’s surface and will provide key information about its mysterious internal ocean, which is thought to be one of the most promising places for life in the solar system. The spacecraft should arrive at Europa in 2030.