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New horizons for distant worlds

Planetary scientist Dr Andrew Prentice can't wait to find out what NASA's New Horizons spacecraft will tell us about Pluto.

As NASA's New Horizons spacecraft speeds towards humanity's historic first encounter with the frozen world of Pluto, over three billion kilometres away planetary scientist Dr Andrew Prentice sits quietly in his office dreaming of the upcoming encounter.

"It's still more than two years away, but it will provide us with such a wealth of new data to examine," says Prentice.

The 60-something lecturer who is now semi-retired after clocking up over 40 years on the job, was recently awarded the Vice Chancellors' Medal for Teaching Excellence at Melbourne's Monash University.

But that doesn't mean he's slowing down.

The Oxford University trained astronomer is still actively researching and sees New Horizons as more than a vehicle for exploring far-off worlds.

"It's a tool that will allow us to test predictions relating to ideas about how the solar system formed," says Prentice, who has made several predictions about our solar system that have been proven correct by NASA missions.

Launched in 2006, New Horizons is now 3.4 billion kilometres away and flying towards the orbit of Neptune, the most distant planet in the solar system.

But it still has another 1.3 billion kilometres to go before reaching Pluto and the Kuiper belt, a place of dark frozen worlds, cometary bodies and icy debris left over from the formation of the solar system 4.6 billion years ago.

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Moon gazing

New Horizons is one of the fastest spacecraft ever built, travelling at over 55,000 kilometres an hour, to reach Pluto before the plutonian winter.

Its historic voyage has already taken it beyond the red deserts of Mars, over the stormy cloud tops of Jupiter, around its moons, and past the orbits of Saturn and Uranus.

It's a neighbourhood Prentice knows well, having successfully predicted the location of a family of new moons in orbit around Neptune in 1989.

"That was possibly my biggest triumph," says Prentice.

"We did the calculations and they showed up right on cue where they should be."

His calculations about the ringed world of Saturn and it's many moons have also proven remarkably accurate.

"Titan is huge, it's bigger than the planet Mercury and my data indicates it would have originally formed independently as a planet only to be later captured by Saturn's gravity," says Prentice.

If his hypothesis is correct, Prentice says Titan should have a slightly oblate structure.

"Well, Titan did turn out to be oblate, and that could only happen if it formed in a free orbit as I predicted," says Prentice.

"I don't want you to think we have all the answers, we still have a lot of work to do which is why New Horizons will be so important."

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Destination Pluto

When it reaches Pluto in 2015, New Horizons will spend five months exploring the dwarf planet and its five-known moons.

It will make its closest approach to Pluto and its largest moon Charon, on 14 July, undertaking hundreds of scientific observations with its onboard instruments, shedding new light on these distant worlds.

According to calculations Prentice made 20 years ago, Pluto and Charon were once a single rocky body covered in a mix of water ice, dry ice and methane ice. But this proto-Pluto object may have spun so fast that the rock and ice separated, flinging the icy outer mantle into orbit to create Charon.

"Charon today, is thus predicted to be a layered ball of dry ice, water ice and methane ices," says Prentice.

He predicts that both Charon and Pluto — which has a rock-graphite core and icy mantle — will be "quite smooth and nearly crater-free, consistent with worlds that once had deep outer liquid mantles."

On the other hand, the four distant moonlets — thought to be icy asteroids that were captured by the Pluto-Charon system — will be craggy, heavily cratered and irregular in shape, he says.

"In addition, Pluto and Charon are expected to be brighter in appearance than the outer moons, whose surfaces are rendered grey and dull through their graphitic component."

While waiting to see if his predictions are correct, Prentice is keeping busy.

"I've been lucky enough to have teamed up with NASA and been involved with many of their planetary missions," he says.

"It's not good to have too many irons in the fire at one time."

"But last year I was working on Cassini with Titan, Mercury which is being visited by Messenger, and the asteroid Vesta which was being studied by the Dawn spacecraft and is now on its way to another asteroid Ceres".

"Then there's all the exciting new data that will be coming out of Mars from the new rover Curiosity," say Prentice

"And the new discoveries lurking at the edge of the solar system, all these new Kuiper Belt objects and what's caused them."

"There's a lot still to do."

Dr Andrew Prentice is a planetary mathematician at Monash University. He is regarded as one of the world's experts on the formation of our solar system. He has made several accurate predictions about our solar system that have been confirmed by NASA. He spoke to Stuart Gary.

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