Five years and 1.8bn miles into its voyage, Nasa’s Juno spacecraft is about to slam on its brakes and fall into orbit around the vast, cloud-striped planet of Jupiter.

With all but the most essential equipment switched off for the critical manoeuvre, Juno will turn away from the sun and fire its main engine at 4.18am Tuesday UK time. All being well, the 35-minute burn will slow the spacecraft to 130,000mph and allow it to be captured by the planet’s immense gravitational field.

“The whole team is really excited that we’re finally arriving at Jupiter,” said Scott Bolton, Juno’s lead investigator at the Southwest Research Institute in San Antonio. “We’ve been waiting for a really long time and finally it’s coming.”



Bristling with instruments, Juno will peer deep beneath Jupiter’s clouds to learn how the planet formed; what drives its brilliant aurorae; and how its complex weather systems produce the giant red spot and the swirling, enigmatic stripes that decorate its outer layers.



The planet formed from an enormous gas cloud 4.5bn years ago under the feeble light of the newborn sun. The material leftover became the rest of the planets, the asteroids and the comets. All would fit easily within the bulk of Jupiter, a planet 11 times wider than Earth and 300 times more massive.

“The primary goal is to understand the recipe for how you make a solar system,” Bolton said. “What we can tell from our instruments can help us learn how planets formed in the first place.”



But first the $1.1bn spacecraft has to arrive safely. Should the rocket burn end too soon or last too long, the mission will be thrown into jeopardy with the probe either failing to reach the right orbit or barrelling straight past the gas giant and onwards to the sun.



“There’s a mixture of tension and anxiety because this is such a critical manoeuvre and everything is riding on it. We have to get into orbit,” Bolton said. “The rocket motor has to burn at the right time, in the right direction, for just the right amount of time.”



A tense moment too, then, for staff at Moog Westcott in Buckinghamshire who built the engine. “The years of design, development, and rigorous technical scrutiny by a passionate and driven team, are defined in one 35-minute burn sequence,” said site manager Rob Selby. “The team here will be watching the Nasa feed with bated breath.”

On Tuesday, the Juno spacecraft will plunge into uncharted territory, entering orbit around the gas giant and passing closer than any spacecraft before.

For mission scientists at Nasa’s Jet Propulsion Lab in California, the first sign that Juno has slowed and swung into orbit will be a change in the pitch of radio signals the probe sends home. It is the same Doppler effect that shifts the tone of sirens on passing police cars. With Juno about half a billion miles away, radio signals from the probe will take more than half an hour to reach mission control.



Juno’s most sensitive electronics are encased in a titanium vault to shield them from lethal radiation belts that are most intense around Jupiter’s equator. To avoid the worst of the circuit-frying environment, Juno will perform highly elliptical orbits that pass over the north and south poles before retreating to a distance of nearly 2m miles. Even so, some equipment onboard will be cooked by radiation long before the mission is over.



Over 37 orbits lasting 14 days each, Juno will come within 2,600 miles of Jupiter’s cloud tops. As cameras and microwave instruments map what lies beneath, scientists will monitor subtle shifts in the frequency of Juno’s transmissions, caused by variations in the planet’s gravitational field due to its uneven internal structure. From the measurements, researchers hope to confirm whether or not Jupiter has a solid core.



Launched in 2011 when Nasa faced a shortage of its favoured power source, plutonium-238, Juno relies on the sun’s rays for energy and is already the most distant solar powered spacecraft from Earth. But even with three massive solar arrays, at such distance from the sun, Juno can generate only 500 watts to power its 29 sensors and nine instruments.

Jupiter’s poles dazzle with aurorae that are wider than Earth and hundreds of times brighter than the northern lights. With data collected by Juno, researchers led by Stanley Cowley at Leicester University hope to nail down the origins of the spectacular displays. On Earth, the celestial light shows happen when energetic particles in the solar wind are caught in Earth’s magnetic field. On Jupiter, they are powered by the immense energy of the planet’s spin.



Hitching a ride on the 3.5m by 3.5m spacecraft are three Lego crew members. The Roman god Jupiter, who drew a veil of cloud around himself to obscure his mischief, and his wife Juno, who was able to see through the clouds, are joined by a telescope-wielding Galileo Galilei, who discovered four of Jupiter’s moons.

Juno’s first close up images of Jupiter are not expected until late August when the spacecraft swoops towards the surface with its cameras switched on. For the next 20 months the probe will steadily build up an unprecedented map of the planet before its instruments finally fail and the spacecraft plunges into Jupiter’s swirling clouds, never to emerge again.