The planet Jupiter might be the second-biggest object in our solar system but we know surprisingly little about this strange, inhospitable world.
Winds rip across its cloud tops at more than 600km per hour and storms perpetually rage across its visible surface.
It has a crushing gravitational pull that sweeps up anything in its path, no matter how big or small. It has a magnetic field of spectacular strength that makes our own seem inconsequential.
It emits so much radiation that it would fry anything left unprotected; and yet 78 per cent of the planet is made up of one of the lightest elements known, helium.
A €1 billion satellite called Juno is set for a rendezvous with this very strange planet come July 4th on a mission that will unlock Jupiter's secrets.
It will reveal what goes on beneath the planet’s cloud tops, tell us whether it has a solid or liquid core and explain where the planet gets is magnetic fields.
"In terms of science, this is quite exciting. It will go into polar orbit and will measure the internal structure of Jupiter," says Kevin Nolan, a lecturer in physics at Institute of Technology Tallaght and the coordinator in Ireland of the international Planetary Society.
Juno carries a battery of instruments that will analyse the planet inside and out, all the while providing close-up images via the "Junocam".
Juno was launched into space on August 11th, 2011, on a 2.8 billion kilometre journey that has taken almost five years to complete. Its speed was boosted during an Earth flyby in October 2013, and it is now only days away from injecting itself into Jupiter’s orbit.
The seasonal fireworks start on July 4th with a 35-minute engine burn that will slow Juno down and allow it to go into a strongly elliptical orbit. The planned ellipse is very elongated in order to get the satellite within 5,000km of the Jovian cloud tops. The orbit also reduces the amount of radiation damage that can be done to the satellite’s sensitive electronics.
These are hidden away in Juno’s “radiation vault”, a thick titanium box that shields the electronics to reduce damage.
Even so, Juno’s experiments are expected to die off one by one as the planned 37 orbits of Jupiter run their course.
The satellite design is unusual in that planners decided to go with solar panels rather than a radioactive generator to power the craft. These will help stabilise the satellite, however, as it turns slowly to allow each of its experiments to take readings as Juno follows a polar orbit.
"This mission is important because we are entering a whole new realm of planetary science," says Dr Deirdre Coffey, a lecturer in physics at University College Dublin and a researcher in the star-formation group at the Dublin Institute for Advanced Studies.
It is the largest planet in the solar system and it holds the key to the formation of our planetary system, she says.
If the current best theory on planetary formation is correct – and this might change as a result of Juno – then the sun began to form at the centre of the solar system while Jupiter began sweeping up material at the periphery of the system.
Life’s big questions
The sun eventually became big enough to light up its own internal fusion reactor, but Jupiter became a repository for the material there at the origins of the solar system. And somewhere in among all that might have been life, Dr Coffey says.
“We want to know where life came from. We want to see how life could form from the original disc,” she says.
Jupiter accumulated material from this disc and retained it and might now hold an answer to how life evolved from that chemistry.
Dr Coffey’s main research is in star and planetary formation, and there is much to discover. “The more you find out, the more you realise you don’t know,” she says.
Nolan echoes this, and says even the most basic of assumptions, such as where the solar system formed, are still to be discovered. “The reason this mission is so important is we don’t know how the solar system formed. This satellite will tell us whether it formed where it is now or whether it formed farther out and then migrated inward,” he said.
It might also help us understand where the Earth got its water.
BY JOVE: PROBING DEEP INTO A STRANGE WORLD
Understand Jupiter and you can understand how the solar system formed, scientists believe. The Juno satellite is designed to reveal Jupiter in unprecedented detail, and in the process answer major questions about how a sun and its planets come to be.
Juno will peer through the clouds to measure the ratio of oxygen to hydrogen, effectively measuring the abundance of water on Jupiter. Knowing this helps to decide which of the various planet-formation theories is correct.
For example, if there are large amounts of water, where did it come from? Was it comet impacts or did the water arise through some other process?
Juno will study Jupiter’s atmosphere and measure its composition, temperature, cloud motions and pressures as it probes deeper and deeper into what lies below.
Learning whether Jupiter has a solid or liquid centre will tell scientists much about its magnetic and gravity fields.
“We believe it has a rocky core but Juno will determine it and measure the structure of the planet,” says physicist Kevin Nolan. “That will tell us much more accurately how Jupiter formed.”
And the satellite’s polar orbit will allow it to get close to the planet’s spectacular light shows: the northern and southern lights at the poles, which are the largest and most spectacular anywhere in the solar system.
After revealing so much, Juno will make the most dramatic of exits, plummeting down through the atmosphere.
It will relay data back until its signal grows weaker and finally fails as it burns up like a meteor. The main reason for this spectacular end is to prevent any possibility that some stray hitchhiking bacteria from Earth might somehow survive to contaminate Jupiter’s moons.
Some, including Ganymede and Europa, might have liquid water, and earthly invaders could theoretically take refuge there and multiply.
