Juno spacecraft takes new close-up photos of the “pizza moon”

The distance to the moon’s surface was only 1,500 kilometers: so close, less than a stone’s throw in cosmic terms, NASA’s Juno spacecraft flew past Jupiter’s moon Io on December 30 – closer than any other mission in the past twenty years. The probe has been orbiting Jupiter since 2016; it was their 57th flight past this gas giant. According to current knowledge, the largest planet in our solar system has 95 natural satellites; Io is the third largest of these and, at 3,643 kilometers in diameter, is slightly larger than Earth’s moon.

Juno captured impressively detailed images of the surface of the moon, which is named after a lover of Zeus (Roman Jupiter). Astronomers also jokingly call Io the ‘pizza moon’ – thanks to its numerous volcanoes, lava flows and sulfur lakes that glow different shades of yellow, the moon’s surface actually resembles a pizza topped with different types of cheese. Io is the most volcanically active known object in our solar system – the total number of active volcanoes on Jupiter’s satellite is estimated at more than 400.

The reason for the satellite’s extreme volcanic activity is the strong gravitational forces acting on Io. The innermost of the four Galilean moons is exposed not only to Jupiter’s enormous gravity, but also to that of the other Galilean moons, especially Ganymede and Europa. These gravitational forces literally mold Io – the surface rises and falls by 100 meters at a time – thus warming the moon. Due to the volcanic eruptions and violent tectonic activity, there are no impact craters on the surface; instead there are calderas (volcano craters) and sulfur lakes.

The spacecraft’s mission isn’t just to take pictures of the moon’s surface. The main goal is to gather information about the type of volcanic activity on the moon, such as a magma ocean that may be hidden beneath the surface. To collect more data, Juno will fly past Io again on February 3, this time just 1,500 kilometers away. For comparison, that’s about three times the distance the Hubble Space Telescope orbits the Earth.

The close approach to the moon – as well as other objects orbiting close to Jupiter – poses risks to the spacecraft. For example, the increased radiation around the gas giant can disrupt the instruments on board. In 2022, during a flight past Io, there was such a sharp increase in radiation that some images were lost.

The spacecraft carries three cameras: the Jovian Infrared Auroral Mapper (JIRAM), which takes infrared images to measure the heat radiated from the volcanoes and craters; next to it is the Stellar Reference Unit, which provides images of the surface in the highest resolution yet; and finally the JunoCam, which records color images in the visible light range. The JunoCam is obviously showing the first signs of wear. The latest images clearly show that the camera is getting old: the dynamic range of the camera is decreasing and the background noise has increased.

NASA is therefore making the raw material available so that amateur astronomers can edit the photos – “to continue to reveal the beauty and mysteries of Jupiter and its moons”, as the US space agency puts it. Some have already responded to the call and edited images, for example adding colors or highlighting details. Here are some examples: