Juno probe reaches Jupiter after five-year journey

The probe will orbit closer to the giant planet than any spacecraft has done before, flying to within 4,667km of Jupiter's swirling cloud tops.

It is approaching Jupiter at 200 times the speed of sound and one mistake could cause Juno to sail helplessly past the gas giant, unable to complete a $1bn mission to peer through its thick atmosphere and map its gargantuan magnetic field.

It is the only solar-powered spacecraft ever dispatched to the outer solar system and confirmation of whether it will successfully fall into the right orbit is not expected until the early hours of Tuesday morning.

Juno will study the planet's composition, gravity, magnetic field and the source of its raging 618kph winds, while a panoramic camera will take colour shots of the planet.

Launched from Florida nearly five years ago, Juno must be precisely positioned, ignite its main engine at exactly the right time and keep it burning for 35 minutes to shed enough speed so it can be captured by Jupiter's gravity. It will also need to survive a circuit-frying radiation storm generated by Jupiter's powerful magnetic field.

The maelstrom of high-energy particles travelling at nearly the speed of light is believed to be the harshest radiation environment in the Solar System.

To cope with the conditions, the spacecraft is protected by special radiation-hardened wiring and sensor shielding.

Its all-important ‘brain’, the flight computer, is housed in an armoured vault made of titanium and weighing approximately 172kg.

Dr Scott Bolton, Juno's principal investigator from Southwest Research Institute in San Antonio, US, said: "We are not looking for trouble, we are looking for data. Problem is, at Jupiter, looking for the kind of data Juno is looking for, you have to go in the kind of neighbourhoods where you could find trouble pretty quick."

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

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

Galileo made wide orbits at distances of hundreds of thousands of kilometres that kept it out of serious danger from the radiation, but still suffered a number of technical glitches.

The spacecraft sent a small probe on a one-way trip through the clouds of Jupiter and was eventually itself crashed on to the planet at the end of its mission.

As a further safeguard, Juno is programmed to follow a long orbital path that avoids Jupiter's radiation belts as much as possible.

Despite these measures, the probe is not expected to last much longer than its planned lifespan of 20 months.

Chief radiation monitoring investigator Heidi Becker, from Nasa's Jet Propulsion Laboratory, said: "Over the course of the mission, the highest energy electrons will penetrate the vault, creating a spray of secondary photons and particles.

"The constant bombardment will break the atomic bonds in Juno's electronics."

Unusually for a robotic space mission, Juno is carrying passengers, three Lego figures depicting the 17th century Italian astronomer Galileo Galilei, the Roman god Jupiter and the deity's wife Juno.

Lego made the figures out of aluminium rather than the usual plastic so they could withstand the extreme conditions of space flight.

A plaque dedicated to Galileo and provided by the Italian Space Agency is also on board.

Juno space probe approaches Jupiter infographic