volcano world comes into view of Juno probe Published 15 December

process of making a series of ever closer flybys.

Already, the spacecraft has passed by the Jupiter moon at a distance of 80,000km, to reveal details of its hellish, lava-strewn landscape.

But Juno will get much, much nearer to Io over the course of the next year, eventually sweeping over the surface at an altitude of just 1,500km.

It's more than 20 years since we've had such an encounter with the 3,650km-wide object.

Space telescope reveals 'incredible' Jupiter views
Tonga volcano eruption continues to astonish
Europa
IMAGE SOURCE,NASA/JPL-CALTECH/SWRI/MSSS
Image caption,
A dedicated Europa mission launches in 2024. It should find the depth of the liquid ocean
"We have a number of objectives besides trying to understand the volcanoes and lava flows, and to map them," said Juno's principal investigator, Dr Scott Bolton from the Southwest Research Institute.

"We're also going to be looking at the gravity field, trying to understand the interior structure of Io, to see if we can constrain whether the magma that's creating all these volcanoes forms a global ocean, or whether it's spotty," he told BBC News.

Io's volcanism is driven by its proximity to Jupiter. It means the moon is subject to immense tidal forces and heating.

Media caption,
Scott Bolton: "Passing Ganymede squeezed and tightened our orbit around Jupiter"

It's a fun time for the Juno mission right now.

Sent primarily to investigate the origin and evolution of Jupiter, Juno has been able to take in bonus observations of the planet's four major moons - Callisto, Ganymede, Europa and now Io.

The spacecraft is picking them off one by one as its orbit around Jupiter narrows.

Media caption,
Fly over Jupiter's northern polar region. Animation produced from Juno imagery by Gerald Eichstädt

It performed its close flyby of Ganymede in 2021, and of Europa earlier this year.

These passes produced some novel insights from Juno's microwave radiometer.

Intended to look deep into the clouds of Jupiter, this instrument has also been able to see down through the ice layers of Ganymede and Europa for tens of kilometres.

These two moons are of particular interest because they're both thought to hide a global ocean of liquid water at depth. The speculation is they might both therefore host some form of life.