Juno mission: Jupiter probe close to entering planet's orbit
A spacecraft, named Juno after the Roman goddess, is close to entering Jupiter's orbit and the "unknown territory" which poses the biggest threat to the historic mission.
It will get closer to the giant planet than any spacecraft has done before, flying to within 2,900 miles of Jupiter's swirling cloud tops.
The probe is expected to begin its orbital entry overnight following a five-year, 1.4 billion-mile journey from Earth.
To complete its risky mission, the unmanned spacecraft will have 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.
Chief radiation monitoring investigator Heidi Becker, from Nasa's Jet Propulsion Laboratory, said: "Juno is going to go into the scariest part of the scariest place that we know about, because we don't know about it. It's the part of Jupiter's radiation environment where nobody has ever been."
Nasa's scientists have also warned the "king of our solar system" poses another danger for the probe, in the form of rings of debris that could derail its efforts.
Scott Bolton, Juno's principal investigator from Southwest Research Institute in San Antonio, Texas, said: "Jupiter also has a ring around it - a ring of debris, dust, meteorites.
"There's a vertical extent of these rings that is not very well known. Juno is to pass through these rings and we do not know know how close to the planet they actually go.
"And if it gets hit, even by a big piece of dust, even a small piece of dust, it can do very serious damage. One of the vulnerabilities that we have to face is the fact that we have to open our engine door so the nozzle is open and vulnerable, we are flying through faster than any other object has ever gone with the nozzle facing forward.
"If any dust is in our way and hits that nozzle it will knock a hole right through the coating that protects the nozzle and allows the engine to burn uninterrupted.
"So that's one of the big gambles - we have done everything we can, we have protected everything we can as best we can, we have modelled it but we're going into unknown territory.
"So you've got the radiation, and you've got this dust and meteorite scare so that's part of what we are facing but we are built like an armoured tank."
Juno will study Jupiter's composition, gravity, magnetic field and the source of its raging 384mph winds.
A panoramic camera will also take spectacular colour photos.
Juno's all-important "brain" - the flight computer - is housed in an armoured vault made of titanium and weighing almost 400lb.
The previous record for a close approach to Jupiter was set by Nasa's Pioneer 11 spacecraft which passed by the planet at a distance of 27,000 miles in 1974.
Only one previous spacecraft, Galileo, which visited Jupiter and its moons from 1995 to 2003, has orbited the planet.
Juno was launched into space by an Atlas V rocket from Cape Canaveral, Florida, on August 5 2011.
The mission is part of the US space agency's New Frontiers programme of robotic space missions which last year saw the New Horizons craft obtain close-up views of dwarf planet Pluto.