A spacecraft destined to become the fastest manmade object in history is set for launch on Friday on a mission that will end in a high-speed crash into the largest planet in the solar system.
The 3.5-tonne probe is due to blast off on an Atlas V rocket from Cape Canaveral in Florida at 4.34pm BST (11.34am local time) on a 2,800 million kilometre voyage that will take it far out into the solar system before looping back around the Earth in a slingshot manoeuvre that will hurl the spacecraft towards its target.
Before Juno arrives at its destination, rocket motors will fire up and set the satellite spinning like a three-bladed propeller so that each of its scientific instruments can get a regular and clear view of the planet.
The five-year journey will bring Juno in over the north pole of Jupiter to begin the first of 33 orbits at speeds of up to 160,000kph. To minimise damage from Jupiter’s intense radiation fields, the spacecraft will follow a highly elliptical orbit that goes far out into space before returning low over the north and south poles.
The spinning satellite will photograph Jupiter’s spectacular aurora and map its intense magnetic and gravitational fields for a year in a bid to understand the planet’s formation and the inner workings that make it one of the most extraordinary bodies in the solar system.
“Juno will help us understand how the solar system formed, and how all the planets formed, from the solar nebula some 4.5bn years ago,” said Jack Connerney, deputy principal investigator on the Juno mission at Nasa’s Goddard Space Flight Centre in Maryland.
“After the formation of the sun, the vast majority of mass left over in the solar system resides in Jupiter. The planet is so massive that none of the material that was originally there could escape its gravity, so Jupiter is effectively a sample of the primitive solar nebula that all the planets formed from.”
A major question Juno will seek to answer is the nature of the dynamo that generates Jupiter’s powerful magnetic field, which is 20,000 times stronger than that of the Earth. On our home planet, the magnetic field is produced by a spinning core of molten iron.
“Jupiter’s magnetic field may be generated by the layer of liquid metallic hydrogen in the planet’s interior, but another school of thought says it may be generated from a layer of molecular hydrogen above that. With a good map of the magnetic field, we should be able to tell which it is,” Connerney told the Guardian.
Other instruments aboard Juno will compile detailed maps of Jupiter’s gravitational field to reveal how heavier elements are distributed throughout the planet, and confirm whether or not it has a sold rocky core.
Stowed away on the spacecraft will be a plaque dedicated to Galileo Galilei, who discovered moons in orbit around Jupiter in 1610, and three Lego figures – of Galileo, the Roman god Jupiter and his wife, Juno.
The electronics aboard Juno are encased in a titanium vault designed to protect components from high levels of radiation, but even with this shielding, the spacecraft is expected to sustain serious damage after a year in Jupiter’s orbit. Any loss of control of Juno could leave the spacecraft in danger of crashing into Europa, one of Jupiter’s moons, where future missions may look for signs of extraterrestrial life, so Nasa controllers have developed a final act for the mission.
“You hear of Nasa missions that go on and on, but to be sure we don’t contaminate the surface of Europa, we are going to send Juno crashing into Jupiter,” Connerney said. “I think we will communicate with Juno until the last moment.”
The Great Red Spot on Jupiter’s flank is a hurricane twice the size of Earth that has raged for 300 years. The storms that build on the planet produce winds up to 600kph and flashes of lightning 100 times brighter than those on Earth.
The gas giant is 1,300 times larger than Earth and made almost entirely of hydrogen. It carries more than twice the mass of all the other planets in the solar system combined.
The intense gravitational forces inside the planet compress the gas to such an extent it forms a vast subsurface sea of liquid metallic hydrogen that reaches more than 25,000km deep. Around 10% of Jupiter is helium with trace levels of heavier elements. The core may be solid rock.