Braving intense radiation, a NASA spacecraft has reached Jupiter after a five-year voyage to begin exploring the king of the planets.
Ground controllers at the NASA Jet Propulsion Laboratory erupted in applause when the solar-powered Juno spacecraft beamed home news that it was circling Jupiter’s poles.
The arrival at Jupiter was dramatic.
As Juno approached its target, it fired its rocket engine to slow itself down and gently slipped into orbit.
Because of the communication time lag between Jupiter and Earth, Juno was on autopilot when it executed the daring move.
The spacecraft’s camera and other instruments were switched off for arrival, so there won’t be any pictures at the moment it reaches its destination.
Hours before the encounter, NASA released a series of images taken last week during the approach, showing Jupiter glowing yellow in the distance, circled by its four inner moons.
Scientists have promised close-up views of the planet when Juno skims the cloud tops during the 20-month, $US1.1 billion ($A1.46 billion) mission.
The fifth rock from the sun and the heftiest planet in the solar system, Jupiter is what’s known as a gas giant – a ball of hydrogen and helium – unlike rocky Earth and Mars.
With its billowy clouds and colourful stripes, Jupiter is an extreme world that likely formed first, shortly after the sun. Unlocking its history may hold clues to understanding how Earth and the rest of the solar system developed.
Named after Jupiter’s cloud-piercing wife in Roman mythology, Juno is only the second mission designed to spend time at Jupiter.
Galileo, launched in 1989, circled Jupiter for nearly a decade, beaming back splendid views of the planet and its numerous moons.
It uncovered signs of an ocean beneath the icy surface of the moon Europa, considered a top target in the search for life outside Earth.
Juno’s mission: To peer through Jupiter’s cloud-socked atmosphere and map the interior from a unique vantage point above the poles.
Among the lingering questions: How much water exists? Is there a solid core? Why are Jupiter’s southern and northern lights the brightest in the solar system?
“What Juno’s about is looking beneath that surface,” Juno chief scientist Scott Bolton said before the arrival.
“We’ve got to go down and look at what’s inside, see how it’s built, how deep these features go, learn about its real secrets.”
There’s also the mystery of its Great Red Spot. Recent observations by the Hubble Space Telescope revealed the centuries-old monster storm in Jupiter’s atmosphere is shrinking.
The trek to Jupiter, spanning nearly five years and 2.8 billion km, took Juno on a tour of the inner solar system followed by a swing past Earth that catapulted it beyond the asteroid belt between Mars and Jupiter.
Along the way, Juno became the first spacecraft to cruise that far out powered by the sun, beating Europe’s comet-chasing Rosetta spacecraft.
A trio of massive solar wings sticks out from Juno like blades from a windmill, generating 500 watts of power to run its nine instruments.