Jupiter space probe Juno arrives at planet after Nasa pulls off 'the hardest thing' it's ever done

“We conquered Jupiter,” a Nasa scientist proclaimed after pulling off what he described as the hardest thing the US space agency had ever done by putting a space probe into orbit around the solar system’s biggest planet.

Named after the Roman goddess Juno — Jupiter’s wife — the spacecraft had spent the last five years travelling 1.8 billion miles (2.8 billion kilometres) and arrived at the gas giant travelling at a speed of 150,000mph.

At the end of its 20-month mission, it will be sent on a one-way plunge into the planet's thick atmosphere as Nasa tries to find out whether the planet has a solid core and answer other fundamental questions about how the solar system was created.

Because of the communication time lag between Jupiter and Earth, Juno was on autopilot when it executed the move so all the Nasa team could do was wait to discover whether it had been successful.

Had the scientists’ calculations been only slightly wrong the £890m probe would have simply drifted off into oblivion.

But a 35-minute engine burn reduced the spacecraft's speed by 1,212mph and Juno slipped into orbit just before midnight east coast time on America’s Independence Day to the cheers of the scientists desperately hoping they’d got it right.

“You've just done the hardest thing Nasa's ever done,” Juno chief scientist Scott Bolton told the team.

"We're there. We're in orbit. We conquered Jupiter.

“This is the one time I don’t mind being stuck in a windowless room on the night of the fourth of July.

“The mission team did great. The spacecraft did great. We are looking great. It’s a great day.”

Also noting the date, Nasa administrator Charlie Bolden questioned whether there was anything more American than “a NASA mission going boldly where no spacecraft has gone before”.

And he said the mission could produce potentially profound new insights.

“With Juno, we will investigate the unknowns of Jupiter’s massive radiation belts to delve deep into not only the planet’s interior, but into how Jupiter was born and how our entire solar system evolved,” he said.

Juno will now face many challenges as it orbits in one of the harshest environments in the solar system, in the firing line for high levels of radiation and high-velocity dust and particles.

Nasa said that its team would perform tests of various systems on Juno and calibrate scientific instruments over the next few months.

“Our official science collection phase begins in October, but we’ve figured out a way to collect data a lot earlier than that,” said Bolton.

“Which when you’re talking about the single biggest planetary body in the solar system is a really good thing. There is a lot to see and do here.”

Juno's “principal goal” is to understand the origin and evolution of Jupiter, Nasa said in a statement.

“With its suite of nine science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter's intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet's auroras,” it added.

“The mission also will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system.

“As our primary example of a giant planet, Jupiter also can provide critical knowledge for understanding the planetary systems being discovered around other stars.”

A 10-strong team of scientists from Leicester University will analyse data on Jupiter's powerful magnetic field, its spectacular auroras, and its dynamic atmosphere. They will combine information from Juno with that from ground-based telescopes on Earth.

Dr Leigh Fletcher said: "What Juno is really trying to do is get down really deep, deeper than we've ever been able to look before.

"From the ground we can look at the high-level stuff and combine it with the deeper data from Juno to produce a 3D picture of the atmosphere."

A key part of the mission will measure Jupiter's internal density from the way the planet's gravity slightly disturbs Juno's orbit.

"If we detect a core that will allow us to understand how the planet formed in the first place," said Dr Fletcher.

"That really is at the heart of the Juno mission. Does Jupiter have some sort of solid rocky core or not? It could have formed with a core, from an embryo of rock and ice, or in a similar way to a star, without a core.”

Studying Jupiter is of great importance to astronomers because of the way its enormous gravity influences the "architecture of the solar system", said Dr Fletcher.

He added: "It causes material to be flung about and we believe it migrated inwards and outwards during the early stages of the solar system's formation.

"In other solar systems we've seen gas giants close to their stars, and maybe they've migrated in. If Jupiter had done that, we wouldn't be having this conversation now."

The Press Associated contributed to this report.