On Independence Day, NASA celebrated a new victory when the spacecraft Juno successfully began its orbit of Jupiter, 540 million miles away from Earth. 

"There's a saying, you know, 'it's not rocket science.' Well today it really was rocket science," says Guy Buetelschies, Director or Space Explorations Systems for NASA.

The mission was launched nearly five years ago to study the composition and evolution of the planet, which is the largest in our solar system. 

Senior Editor of Sky and Telescope Magazine,  Kelly Beatty ( @NightSkyGuy) explains why Juno is such a big deal.

“It’s a big deal in this sense: when we send a space craft to Mercury, it’s ‘What happened on Mercury?’ when we send a space craft to the moon, it’s ‘what happened on the moon?’ Here, we’re talking about what happened on our solar system when it formed a 4.5 billion years ago.”

This isn’t the first time NASA has sent a probe to explore Jupiter. The unmanned spacecraft Galileo orbited Jupiter and its moons for eight years beginning in 1995. But Beatty says Juno’s mission is much different.

“This is the up-close and personal mission, where the spacecraft flies…very close to the cloudtops.”

Jupiter basically has the same composition as the sun: helium and hydrogen in solar proportions, plus some carbon, nitrogen and oxygen. And according to Beatty, it’s also the most unchanged planet since the beginning of the solar systems. “In Jupiter, we’re seeing a sort of cold, trapped, preserved chunk of solar system when it first came together.”

So if NASA can collect information on how Jupiter was formed, we will also get a better understanding of how all the planets in our solar system came to be.

One of Juno’s principal objectives is to probe for water on Jupiter. In theory Jupiter should have a lot of water, but when Galileo probed into the planet’s atmosphere it found very little. A second probe will refine scientist’s knowledge of how water is distributed throughout the solar system, and could help determine where Earth’s water came from as well.

Before Juno ends its mission in 2018, it will also examine what’s going on inside the solar system’s largest planet.

"On paper, [Jupiter] should have a really massive core many times the mass of Earth made of rock. But, we don’t know. And there’s a school of thought that like, the rock never settled out, and it’s just kind of swimming around on the inside," says Beatty. 

Juno’s third objective is to gather information on how the massive radiation belt interacts with the planet’s polar regions.