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Why Juno is as vital as putting man on the moon

It is, say experts, the hardest thing Nasa has ever attempted. Little wonder, then, that the cheers of its jubilant scientists reverberated around the world last week as the spacecraft Juno arrived in the Jovian system after an epic five-year, 1.8 billion-mile (2.8 billion km) journey.

Why Juno is as vital as putting man on the moon

An artist’s depiction of Nasa’s Juno spacecraft above Jupiter’s north pole. Its most important observations will be the planet’s magnetosphere. PHOTO: NASA/JPL-Caltech VIA REUTERS

It is, say experts, the hardest thing Nasa has ever attempted. Little wonder, then, that the cheers of its jubilant scientists reverberated around the world last week as the spacecraft Juno arrived in the Jovian system after an epic five-year, 1.8 billion-mile (2.8 billion km) journey.

“Welcome to Jupiter,” said mission control commentator Jennifer Delavan as, in the background, researchers jumped up and down, hugging and clapping.

It was a scene that made me smile. Back in November 2014, I experienced the same feeling of elation after robot probe Philae — a project I had worked on with colleagues for almost 20 years — finally landed on a comet, after detaching from the Rosetta satellite.

Juno is a space suicide mission like no other. Indeed, it sounds like the plot of a Hollywood sci-fi blockbuster — the craft even had the courtesy to arrive at Jupiter on America’s Independence Day.

Its mission? To solve the mystery of what lies beneath the planet’s swirling storm clouds. We might be able to see it from Earth with the naked eye, but scientists know relatively little about this vast gas giant, which produces the most spectacular aurora in the solar system.

We know that 1,000 Earths could fit across its equator, and that it takes 12 years to go round the Sun. We know that the main bulk of the planet is composed of hydrogen and helium. Everything else is pretty much up for grabs.

Once it arrived at the Jovian system on Monday, Juno — the first craft to travel this deep into space using only solar power — had to carry out several complex manoeuvres.

Not only did it have to withstand the planet’s vast radiation field, the £890 million (S$1.6 billion) probe also needed to survive intense turbulence and dodge space debris. Like its neighbour, Saturn, Jupiter is surrounded by a ring of dust and rock.

As Juno’s chief scientist Scott Bolton said: “It’s a monster, it’s unforgiving, it’s relentless. It’s spinning around so fast. Its gravity is like a giant sling shot, slinging rocks, dust, electrons, whole comets. Anything that gets close to it becomes its weapon.”

No wonder, then, that others simply describe it as the “biggest, baddest planet in the solar system”.

But the plucky little Juno probe, which launched from Cape Canaveral on Aug 5, 2011, survived and plunged into an orbit that circles Jupiter pole-to-pole. Its mission is designed to last at least 20 months, and during that time, Juno — named after the Roman goddess and wife of Jupiter — will circle the planet 37 times.

Beneath its titanium outer shell lie nine sensitive instruments, designed to do what no craft has achieved before: Peer into Jupiter’s heart.

It will fly 4,184km above the cloud tops — 4,828km closer to the surface than any other mission has ever achieved.

Of course, this is not the first time scientists have tried to get close to our largest planet.

Just over 40 years ago, Nasa’s Pioneer 10 flew past Jupiter at a distance of 130,356km, and took the first close-up images. They showed us that the planet’s striped appearance — visible from the ground through telescopes — is probably caused by weather systems. It also recorded Jupiter’s great red spot, an enormous vortex of high pressure that appears like a storm and spreads out to three-and-a-half times the Earth’s diameter.

Most importantly, that mission hinted at the strength of Jupiter’s invisible magnetosphere — the vast magnetic field that surrounds it, full of charged particles from the Sun, nearby planets and cosmic radiation. Researchers have since theorised there must be a solid body beneath Jupiter’s storm clouds in order to create this magnetosphere — so big that, if visible, it would appear the size of two full moons in the sky from Earth.

Six years after Pioneer 10 came Voyager 1 and Voyager 2 — which recorded active volcanism on the planet’s innermost moon, Io, and took pictures of its smallest moon, Europa, that suggested it has an icy surface with an ocean beneath.

Then, between 1995 and 2003, the Galileo orbiter mapped the planet. The probe, designed to enter Jupiter’s atmosphere, burned up within an hour of release as the temperature and pressure grew too great.

And so now our hopes rest on Juno.

The craft will go closer, for longer, than any other of Jupiter’s visitors, and its colour camera, nicknamed the JunoCam, will snap close-ups of clouds and polar regions.

Meanwhile, the on-board instruments will refine what little we know about its composition, which has higher amounts of sulphur, nitrogen and noble gases than expected from a planet basically formed from gases left over from the Sun’s creation.

This will bring us closer to answering the question: How and where Jupiter was formed? Current theories suggest it started closer to the Sun, moving outwards to its current position over a period of a few million years. All may soon be revealed.

Juno will also investigate Jupiter’s weather systems, with a view to applying what we learn to our understanding of the Earth’s own weather. However, Juno’s most important observations will be focused on the magnetosphere.

Since the Voyager missions, it has been known that the Saturn-like ring around Jupiter is formed by sulphur dioxide released by volcanism on the moon Io. The planet’s magnetic field traps dust from Io and accelerates it, producing the intense radiation for which Jupiter is notorious.

Thanks to the improved data from Juno, this simplified picture will now be redrawn, allowing us to understand more completely the formation and behaviour of Jupiter’s shimmering aurorae — it frequently puts on a display of fireworks that crowns the poles of the planet.

Of course, nothing is certain and Juno still faces huge challenges. The Jovian system is one of the harshest environments in space, and threats from radiation and high-velocity debris are constant. What is more, in August, the Nasa team will endeavour to perform another tricky manoeuvre to place the craft even closer to the planet’s surface.

And all this before, eventually, the craft succumbs to Jupiter’s intense radiation and plunges deep into the atmosphere to avoid colliding with its moons.

But, should all go according to plan, this could finally be the mission that provides the insights we scientists crave — a new discovery about the origins of the solar system. It may not be as sexy as putting a man on the moon, but it is something I believe we should care as deeply about.The Daily Telegraph


Monica Grady is Professor of Planetary and Space Science at the Open University

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