On 4 July, the Juno spacecraft went into orbit around Jupiter, beginning its mission to probe the interior of our solar system’s largest planet. It has only just started collecting data and the first results are not expected until September; undoubtedly it will be years before we really know what we have found there.

Even though my own research has little to do with Jupiter, I have a personal stake in this spacecraft. Ten years ago, when Nasa was deciding what its next big mission would be, it solicited proposals from the community, and Juno was one of five missions reviewed by a panel of experts. I was one of the experts.

The Juno proposal addressed a fundamental question about gas giant planets such as Jupiter and Saturn. (Hundreds of such gas giants have been discovered orbiting other stars, as well.) Are they lumps of gas that did not quite grow big enough to become stars themselves while they were forming within a larger star-forming gas cloud? Or did they start as solid planets that grew big enough to trap lots of gas from such a cloud? Whichever theory turns out to be true will shape how we understand the origins of stars and planets.