The probe, known as Juno and powered only by the sun, took almost five years to reach the solar system's largest planet.

Juno left Earth in 2011, travelling nearly 3 billion kilometres to reach its destination.

And on Tuesday, July 5, it did just that.

"All stations on Juno coordination, we have the tone for burn cut-off on Delta B. Roger, Juno, welcome to Jupiter."

Juno's entry into Jupiter's orbit was a nervous half-hour wait for scientists at the United States space agency, NASA.

It had to fire a rocket engine to slow down its approach to the planet and get caught by the planet's gravitational pull.

Juno needed to be precisely positioned, ignite its main engine at exactly the right time and keep it firing for 35 minutes.

If anything went even slightly wrong, the probe would have sailed helplessly past Jupiter.

Thankfully, for NASA Juno program executive Diane Brown, it went smoothly.

"I mean, it's overwhelming. The team, the amount of time and effort everyone put into this, and the risks that were overcome, it's amazing. I mean, the more you know about the mission, you know just how tricky this was, and, to have it be flawless, I mean, I can't really put it into words. You imagine what it might feel like, but to actually have it, to know we can all go to bed and not worry about what is going to happen tomorrow, is pretty awesome. That's really all I can say. It's just amazing."

Dr Alan Duffy is an astronomer and a researcher at Melbourne's Swinburne University.

He, too, is amazed at the accomplishment.

"This is an absolutely insane mission. I am still astounded that they managed to succeed. With pinpoint precision, fly through a window in space barely 20 kilometres wide -- that's equivalent to hitting the absolute centre of a bullseye when you've thrown the dart from one side of the city to the other. And to do this all with the very real threat that your mission ... if you burn for too long, if you slow down too much, it will plunge in the cloud of Jupiter, or, if you don't burn for long enough, you'll actually bounce off and head off into space. And they managed to get it, after five years, to within a second, which is just an astounding achievement."

Juno will begin sending information back to Earth while studying what lies beneath Jupiter's thick clouds and mapping the planet's gargantuan magnetic fields.

Each orbit it will take around Jupiter will go for 14 days.

It will also look for evidence that Jupiter has a dense inner core and measure how much water is in the planet's atmosphere.

So why is the mission significant?

Lead scientist Scott Bolton says it helps scientists understand the formation of the solar system.

"You know, what Juno is really about is learning about the recipe for how solar systems are made. Scientists don't really understand how the planets are made. We know, after the sun formed, something happened and we were able to form Jupiter. It took up more than half of the material that was left over, and it's a little bit different than the sun, and we don't completely understand that, and that's really the first step in that recipe."

Dr Alan Duffy says Juno has a key role in explaining the importance of science to the general public, especially young people.

He says Juno is just as important an accomplishment as humans landing on the moon.

"This is our moment, this is our time, with space missions like Juno, to inspire that next generation and have them be even more ambitious and perhaps look back at Juno as a quaint experiment and they've achieved something even greater. But, for now, Juno has set the bar* incredibly high for future space missions."

Dr Brad Tucker is an astronomer at Mount Stromlo Observatory, at the Australian National University.

He says the Juno mission is not only exciting for space scientists.

"When you start to realise that the complex questions that even the most uninterested in science think about -- Are we alone? How did we get here? Where are we going? -- by understanding the origins of the solar system, and how things have evolved from it and can life even exist on a system like Jupiter, really puts into perspective that that thing that you see in the night sky, that little dot, is where we just sent that probe to answer the origins of the solar system and where we are going."

And Dr Tucker says the Juno mission also raises questions about why Australia does not have a space program.

"It is kind of sad how Australia, as a nation, is behind. I mean, if you look at the top 35 countries of the Economic Development Forum, there's only two that don't have a space program, and Australia is one of them. I mean, New Zealand just started a national space program. And it always goes back to this: Why should we fund space and space travel and astronomy costing billions of dollars? The simple answer I always like to give is, when we think of doing things in space or probes, these sorts of things, these are very hard, complex problems, and, when you have to answer and solve these problems, you get complex and challenging and advanced solutions that do help us as humans and us as society."

Swinburne University's Alan Duffy agrees.

"Australia itself can pioneer and earn the economic benefits from this innovation, because fundamentally exploring space is a way to inspire our engineers and scientists who think big, think in incredibly advanced ways, and that technology inevitably finds its way into the broader economy. NASA is able to return some $2.60 on every dollar the US government invests, and that's simply because, the technologies we create and the employment and advanced skills that we develop, those are what drive economies forward. And that's what I look forward to seeing more of in Australia."

NASA says it spent US$1 billion on the mission, which is expected to last for 20 months before being crushed in Jupiter's atmosphere.

The previous record for a close approach to Jupiter was set by NASA's Pioneer 11 spacecraft, which passed by the planet at a distance of 43,000 kilometres in 1974.

Only one previous spacecraft, Galileo, which visited Jupiter and its moons from 1995 to 2003, has orbited the planet.