MIAMI • Ducking through intense belts of violent radiation as it skimmed over the clouds of Jupiter at over 209,000kmh, Nasa's Juno spacecraft finally clinched its spot yesterday in the orbit of the solar system's largest planet.
It took five years for Juno to travel this far on its US$1.1 billion (S$1.48 billion) mission, and the moment was one that Nasa scientists and space enthusiasts had eagerly - and anxiously - anticipated.
At 11.52am Singapore time, a signal from the spacecraft announced the end of a 35-minute engine burn that left it in the grip of its desired orbit around Jupiter.
Cheers and applause erupted at the mission control centre at Nasa's Jet Propulsion Laboratory in California, which is managing Juno.
"We're there. We're in orbit. We conquered Jupiter," Dr Scott Bolton, Juno's principal investigator, told reporters.
Status messages for each manoeuvre of the spacecraft came in as expected. The length of the engine firing turned out to be within one second of what had been predicted.
We're there. We're in orbit. We conquered Jupiter... Juno is really searching for some hints about our beginnings, how everything started. But these secrets are pretty well guarded by Jupiter.
'' DR SCOTT BOLTON, Juno's principal investigator, on the spacecraft's breakthrough mission.
Juno is just the second spacecraft to enter orbit around Jupiter. Nasa's Galileo spacecraft, launched in 1989, spent eight years there surveying the planet and its many moons. But except for a probe that parachuted into Jupiter's atmosphere, Galileo did not have the tools that Juno does to delve into what lies beneath Jupiter's clouds.
"We have a chance with Juno to go back and study the planet in its own right," Dr James Green, the director of planetary science at Nasa, said on Monday.
Jupiter, most likely the first planet formed after the Sun, is believed to hold the key to understanding the origins of our solar system. How much water it contains and the possible presence of a rocky core could reveal where in the solar system Jupiter was created and provide clues to the early days of other planets.
"Juno is really searching for some hints about our beginnings, how everything started," said Dr Bolton. "But these secrets are pretty well guarded by Jupiter."
Juno is equipped with eight science instruments, including a camera which prior to orbit captured a video of Jupiter and its moons gliding around it at different speeds.
Dr Bolton repeatedly described Jupiter as "a planet on steroids" in discussing the unprecedented dangers that Juno was facing.
Ensnared by Jupiter's gravity, Juno accelerated quickly to its rendezvous with the planet, passing within the orbit of Callisto and Ganymede, two of the main moons, late on Sunday and early on Monday. It zoomed past the other two, Europa and Io, on Monday.
Juno has been on its own since last Thursday, performing a programmed sequence of actions. Yesterday morning, it passed over Jupiter's north pole and through a region that Dr Heidi Becker, the leader of Juno's radiation monitoring team, described as "the scariest part of the scariest place".
In this belt of radiation, electrons bouncing back and forth at nearly the speed of light could have knocked out the computer and other electronics. "They will go right through a spacecraft and strip the atoms apart inside your electronics and fry your brain if you don't do anything about it," Dr Becker said.
But a titanium vault built for Juno proved up to the task of shielding its crucial systems.
Then Juno's main engine began firing to slow it enough to be captured by the planet's gravity.
The spacecraft also passed through the plane of Jupiter's diaphanous rings. Although the mission planners had chosen a place that they thought would be clear, they could not be sure, and even a piece of dust colliding with a spacecraft moving at over 209,000kmh could have caused considerable damage.
Juno passed within 4,700km of Jupiter's cloud tops, aiming for a spot tens of kilometres wide after a journey of 2.7 billion km. It headed outward again, away from Jupiter. After the end of the engine burn, it pivoted so that its solar panels were again facing the Sun.
Juno's three 9m-long panels with 18,698 solar cells generate a mere 500 watts to power the spacecraft and its instruments.
Its inaugural lap around the solar system's most massive planet - the fifth from the Sun - will last 53 days. On Aug 27, Juno will swing back for its first good close-up look at Jupiter. It will fire its engine again on Oct 19 to move to a 14-day orbit when the science measurements begin in earnest.
Juno should circle the planet 37 times before finally making a death plunge in 2018 to prevent it from causing damage to any of Jupiter's icy moons, which Nasa hopes to explore one day for signs of life.
"Now the fun begins, with science," Dr Bolton said.
NEW YORK TIMES, REUTERS, AGENCE FRANCE-PRESSE,