Juno arrives at Jupiter, prepares to enter orbit

How Juno might look in orbit around Jupiter (NASA)
How Juno might look in orbit around Jupiter (NASA)

Juno's five-year mission to Jupiter is almost over, but the real work is set to begin.

The three-tonne spacecraft arrives at the gas giant on Tuesday after travelling 2.8 billion kilometres through space.

Last week Juno entered Jupiter's magnetosphere, where Jupiter - not the sun - becomes the main influence on particles and magnetic fields. This was seen in data sent back by Juno, astronomers calling the sudden shift the "bow shock".

Juno arrives at Jupiter, prepares to enter orbit

"The bow shock is analogous to a sonic boom," said William Kurth of the University of Iowa, one of the lead investigators. "The solar wind blows past all the planets… and where it hits an obstacle, there's all this turbulence."

Barring the sun, Jupiter's magnetosphere is the largest field of influence in the solar system.

"If Jupiter's magnetosphere glowed in visible light, it would be twice the size of the full moon as seen from Earth," says Dr Kurth.

Juno passed through the orbit of Jupiter's outermost moon Callisto on Monday morning at about 6am.

Though Juno is set to 'arrive' at Jupiter itself tomorrow, it won't be touching down - Jupiter has no solid surface to land on. Instead, at about 3:18pm tomorrow (NZT), Juno will fire its main engines for 35 minutes, putting it into orbit.

"We are ready," says Scott Bolton from the Southwest Research Institute in San Antonio.

After getting into orbit, Juno will conduct at least a year's worth of scientific observations, circling the planet 37 times and getting within a few thousand kilometres of its clouds.

"The science team is incredibly excited to be arriving at Jupiter," says Dr Bolton. "The engineers and mission controllers are performing at an Olympic level getting Juno successfully into orbit. As Juno barrels down on Jupiter, the scientists are busy looking at the amazing approach science the spacecraft has already returned to Earth.  Jupiter is spectacular from afar and will be absolutely breathtaking from close up."

Juno launched in August 2011, did an orbit of the sun before flying by Earth in September 2013. The speed it picked up as a result allowed it to cruise out to Jupiter using minimal fuel.

It currently takes information sent back by Juno 45 minutes to reach Earth. This will change during the year it spends in orbit around Jupiter, as Earth travels around the sun much more quickly and has a smaller orbit.