Juno will be travelling at 265,000 kph when it arrives at Jupiter

By Will Goodbody, Science & Technology Correspondent

Over the next few days, indeed months, you are likely to hear quite a bit about a spacecraft called Juno and its mission around Jupiter.

It’s an exciting project, which could yield many answers to questions about the origin of the planet, and of the solar system as a whole.

Why Jupiter?

Jupiter is the largest planet in our solar system.

Yet despite its size, we don’t know all that much about it.

We know it’s about 11 times the circumference of Earth, that it orbits the Sun at a distance of five times that of the Earth.

We also know it is made primarily of hydrogen and helium, that it is covered in raging storms, and that its massive magnetic field that is 20,000 that of Earth’s generates radiation levels which fry pretty much anything that gets too close.

But we don’t know how it was formed or where in the solar system it was created. Nor do we know what causes the aurora around its poles.

We don’t know what lies beneath the layers of helium and hydrogen. Does it have a solid core of ice or rock, or is it just all built around dense gases?

There’s little we know about its atmosphere too. What causes those storms, for instance, and the Great Red Spot?

So Juno is going to find out.

But haven’t we sent probes to Jupiter before?

Yes, we have.

But none has travelled as close as Juno hopefully will.

It will come within 4,667 km of the cloud tops on the planet – a stone’s throw away in space exploration terms.

Before Juno, the nearest a spacecraft has got to Jupiter was 43,000.

That was Nasa’s Pioneer 11 in 1974.

It will also be only the second time that a spacecraft has orbited Jupiter – the first one being Galileo between 1995 and 2003.

It had to stay that distance away because of the harsh conditions closer to the planet – and even then, it didn’t get through unscathed.

Jupiter aurora

If Jupiter really is so nasty, then how is Juno going to survive?

Juno has a special titanium vault weighing 400lbs, in which the instruments are housed in order to shield it from the radiation.

It will also be in elliptical shaped orbits, which should in theory minimise its exposure to the worst of the risk.

The plan is that at around 4:18am tomorrow morning Irish time, after a five year 2.8 billion kilometre journey, a reverse booster will automatically fire on board Juno as it hurtles towards Jupiter at 265,000 km/h.

If it doesn’t fire correctly or for long enough, Juno will simply fly straight past Jupiter, and that will be that.

But if all goes to plan, and the thruster burns for the 35 minutes it is programmed to, then the gravity of the planet should capture it and place it in the orbit.

Initially it will be in an elliptical path that will take 53.5 days to complete. It will do two of these, before firing its engines again in October to move closer to the planet.

Once in the new orbit, which will last 14 days, the craft will commence its science experiments.

What will that involve?

As you would expect, Juno is packed full of instruments and cameras to capture all sorts of measurements while carrying out those orbits.

But broadly speaking, it has four primary science purposes

First, it will work out how and where in the solar system the planet was formed by measuring its water and oxygen levels.

It will also delve into the swirling belts, zones, clouds, jetstreams and storms of the atmosphere, measuring the composition, temperature and cloud opacity.

It will map Jupiter’s magnetosphere – that’s the massive region of magnetic field that spreads out into space to a size similar to that of our own moon, and investigate what’s causing amazing auroras that look like our own aurora borealis at its poles.

Finally it will probe Juno’s interior structure by mapping its gravitational and magnetic fields to establish is the core beyond the layers of hydrogen and helium we know about made of a solid material like rock or ice, or something else entirely.

That’s all very interesting, but is there a big picture to all this?

Yes, there is.

That is to learn more about the history of the formation of our solar system, including where we may have come from.

If we can figure out when, where and how Jupiter was formed, it should shed new light on the rest of the planets and the Sun, and provide new insight into how planetary systems form and develop in our galaxy and beyond.

There are around five main theories about where in the solar system Jupiter first came together.

Scientists hope that by figuring out how much water there is on the planet, they will be able to tell whether it formed out of blocks of ice, or not.

That will help them to establish whether Jupiter was made around its current distance from the Sun, or whether it was formed in closer.

And obviously if it formed elsewhere in the system, then that has implications for the formation of the other planets and the Sun.


What does Juno look like?

Juno is part of a $1.3bn mission that launched August 5th 2011 from Florida.

It is 3.5 metres high and in diameter – about the size of a small car.

But it also has three solar arrays which when fully extended are nine meters long.

So in total it is wide and long enough to fill a basketball pitch,

They need to be this big because Juno is solar powered, and needs to be able to pick up the sunlight, even though it is very far away.

The panels generate 500 watts of power.

So how long is all this going to take?

In total the plan is for Juno to complete 37 orbits of Jupiter.

Because the environment is so hostile, there is no guarantee that will happen.

But if it does, and the mission objectives have been met, then Nasa will purposely guide Juno down into the atmosphere of Jupiter where it will burn up in early 2018.

That’s because Nasa wants to avoid the risk of the craft crash landing on one of Jupiter’s moons and potentially contaminating it with bacteria which had inadvertently been transferred from Earth.

But it won’t just be the craft that will meet a fiery, radioactive end.

Also on board are three Lego figures depicting the astronomer Galileo, the Roman god Jupiter, and the deity’s wife Juno, after which the craft is obviously named.

It sounds pretty interesting. Anything else I should know?

Juno is a mission of firsts in many respects.

It will be the farthest solar powered spacecraft from Earth, the first space mission to orbit an outer-planet from pole to pole and the first space mission to fly as close as 2,600 miles to Jupiter’s cloud tops.

It will also be the first mission to be designed to operate in the heart of Jupiter’s radiation belts and the first spacecraft to fly 3D-printed titanium parts.

And it will take the highest-resolution images of Jupiter in history.

Stunning pictures we will should hopefully start seeing in just a few weeks time.

Comments welcome via Twitter to @willgoodbody

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