Juno enters Jupiter's orbit after 5-year journey

"We are there. We conquered Jupiter," exclaimed NASA's principal investigator, Scott Bolton, as its $1.1 billion spacecraft, Juno, entered the orbit of the solar system's largest planet at 3:18 gmt.

Launched five years ago from Cape Canaveral, Florida, Juno travelled 1.7 billion miles (2.7 billion kilometres) since then. Its entry into Jupiter's orbit marks the beginning of a 20-month mission with the objective of unravelling the mysteries of the gigantic planet.

What does Juno's successful 'arrival' at Jupiter mean?

Juno is not the first spacecraft to orbit Jupiter, but its path will bring it closer to the planet than its predecessor, Galileo, which launched in 1989.

Galileo found evidence of subsurface saltwater on Jupiter's moons Europa, Ganymede and Callisto before making a plunge into the planet's atmosphere in 2003 at the end of its mission.

Juno's orbital track is closer than Galileo's – this time within 3,100 miles (5,000 kilometres) above the planet's opaque clouds and powerful radiation belt.

Through the mission, scientists hope to find out how much water Jupiter holds and the make-up of its core which will provide a picture of how the planet was formed billions of years ago.

Jupiter's origins in turn affected the development and position of other planets.

Jupiter orbits five times farther from the sun than Earth, but it may have started out elsewhere and migrated. Its immense gravity also diverts many asteroids and comets from potentially catastrophic collisions with Earth and the rest of the inner solar system.

In a nutshell, Juno's mission will also provide clues about the location and the formation of Earth's 'friendly' atmosphere.

"The question I've had my whole life that I'm hoping we get an answer to is 'How'd we get here?'" Bolton said.

The mission will also offer a peak into Jupiter's 'Great Red Spot', a storm bigger than Earth that has been raging for hundreds of years.

Will Juno be able to survive its dance around Jupiter?

A 100 million X-rays in the course of a year. That's how Heidi Becker, senior engineer on radiation effects at NASA's Jet Propulsion Laboratory, described being around Jupiter's radiation belt, the 'scariest place where nobody has ever been."

Those high-energy electrons, moving at the speed of light, "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," Becker said.

"So we did a lot about it," she added, describing the half-inch-thick layer of titanium that protects the electronics in a vault to bring the radiation exposure down.

The mission

Juno which is named after the Roman goddess—the wife of Jupiter, the god of the sky in ancient mythology—is equipped with star tracker cameras and computers and science instruments.

Juno's inaugural lap around the solar system's most massive planet will last 53 days. Subsequent orbits will be shorter, about two weeks each.

Initially, the spacecraft will attempt to 'see' beneath Jupiter's clouds, orbiting the planet from pole to pole and sampling its charged particles and magnetic fields.

Juno should circle the planet 37 times before finally making a death plunge in 2018, to prevent the spacecraft from causing damage to any of Jupiter's icy moons, which NASA hopes to explore one day for signs of life.