To learn about the formation of the solar system, Jupiter is - by far - the largest piece of the puzzle. "It's really big," Scott Bolton, principal investigator on the Juno mission, told IBTimes UK. "It's the biggest. In this case, when you're trying to learn about the solar system, size matters.
"We have a planet that is bigger than all the other planets. All the other planets could fit inside Jupiter and there would still be room left over."
The most popular theory of how the solar system formed involves the collapse of a cloud of gas and dust. The vast majority of this mass collected at the centre to become the Sun, while the rest started clumping together to form the planets, moons, asteroids and comets.
In this process, Jupiter managed to collect more than half of the material left over, becoming the biggest planet. Because of its sheer size, it managed to hold onto all of its elements and the original material it was formed with.
"In many ways by going back and looking at Jupiter, we are turning back the clock to try to understand the very first steps that allowed the sun to form. Then the planets formed to be a little bit different. That little bit of difference is key to our existence. So studying Jupiter is the only way you're going to learn about that first step."
Bolton said that, at present, scientists have been unable to come up with a theory to explain how Jupiter came to be – in terms of what it looks like and what it is formed from. "Earth, and most of the planets to some extent, have lost our history," Bolton said. "But Jupiter has managed to hold on to it, so if you want to look back in history and say what was it like, you need to explain how Jupiter formed."
Juno is set to arrive at Jupiter on 4 July, when it will enter the planet's orbit. It will then start its scientific mission – looking at Jupiter's atmosphere, magnetic field, its interior structure, among other objectives. "I want to see how much water is in there and if there's a core of heavy elements in the centre. They're two of the biggest outstanding questions. Then something that's a little bit easier to grasp is how deep the zones and belts are.
"We see these beautiful stripes on Jupiter and giant storms like the great red spot and I'm very interested to learn how deep do those dynamics go. Presumably the giant red spot has lasted for hundreds of years, it must have very deep roots. But no one really knows."
But the question of its origin, for Bolton, is the main goal. "We'd like to know the whole recipe for solar systems. That's what we're after. We're at the first step – what's the first part of the recipe? What's the ingredient list? We don't really know that yet.
"What we want to know is: how do you make planets? How do you make a solar system? Where did we come from? I want to learn about the origin of Earth, Mars, the comets, the asteroids, all the planets. That first step is very important because there's something fundamental about the difference between making a star and making a planet. And that's what makes Jupiter special."
But further to this, the information the Juno mission provides will help shed light on the formation of other solar systems. When Juno went through Nasa's approval process, Bolton said it was one of the first missions that had support from all the different divisions.
"It's been a long time coming. For different reasons. As we learn about Jupiter through previous spacecraft – Voyager and Gallileo both went there – we learned enough to refine our questions. We also learned enough to realise we don't understand some really basic stuff.
"Everybody wanted Juno because that's our example of a giant planet and if we're going to learn about how other solar systems form, which we're discovering now in other planetary systems, we've got to understand our own. It will be applied to all of these exoplanets. They may not all be the same but we can compare other solar systems to our own, which we're already doing, and of course, learning how Jupiter formed will shed light on giant planets around other stars."