European Space Agency (ESA) scientists are relishing the moment when they get to see their cherished baby, Rosetta, which was hoisted aloft in 2004 in one of the most extraordinary missions in space history.

Rosetta is on a 10-year, 7.1-billion-kilometre (4.4-billion-mile) trek that will lead it to a lonely wanderer of the solar system.

If all goes well, Rosetta will team up with Comet 67/P Churyumov-Gerasimenko in May 2014 before dispatching a fridge-sized lab, Philae, that will anchor to the rock's surface and look for clues about the solar system's primal past.

Thereafter, Rosetta will shepherd the comet for two years, monitoring it with robot eyes on its blaze around the sun.

Before then, though, the probe has to pick up speed -- and Earth's gravity, used as a slingshot, is the key.

At 0746 GMT on Friday, Rosetta will be at its closest point to home, ESA says.

The craft will zip over the Indian Ocean at a height of 2,481 kms (1,550 miles) at 109 degrees latitude east, eight degrees longitude south, or just south of the Indonesian island of Java.

"It will speed past Earth at 13.3 kilometers per second," equal to 47,800 kph or 29,925 mph, ESA says. "The gravity-assist will increase the spacecraft's speed by 3.6 km/s (12,960 kph, 8,100 mph) with respect to the sun."

Astronomers hoping for a glimpse are best placed if they are in the southern hemisphere and have "at least a medium-size telescope," with an aperture preferably of more than 300mm (12 inches), says Amruta Mehta on ESA's blog (http://webservices.esa.int/blog/blog/5/).

Several instruments that are usually inactive during the odyssey were turned on one by one on Wednesday, giving the Rosetta team a chance to see how the gadgets have coped with deep chill and hibernation.

The probe will turn its scientific camera system, OSIRIS, towards the moon to hunt for water there.

Other instruments will scan Earth's atmosphere and magnetosphere, looking for aurorae -- the spectacular collision between the planet's magnetic field and particles blasted from the sun.

The British magazine New Scientist says the flyby could also shed light on an anomaly first spotted in 1990: spacecraft get a tiny, unexpected acceleration, in the order of just a few millimetres (fractions of an inch) per second, in a gravity assist.

Scientists have ruled out factors such as a deviation in Earth's shape or lingering atmospheric drag to explain the quirk, the magazine says on its website.

This has led some to the exotic conclusion that earth's rotation may be distorting the fabric of "space-time" more than expected, which if so would require a fix to Einstein's theory of general relativity -- the currently accepted theory of gravity.

It will be the fourth time that Rosetta has played space billiards in its long mission.

Two previous flybys used earth and the other used Mars to gain speed. The craft is scheduled for a close encounter with asteroid 21 Lutetia in July next year.

Astronomers believe that comets are primitive rubble left over from the making of the solar system.

Understanding their composition can help explain how planets formed from discs of dust and gas, and maybe even how life was kickstarted on Earth.

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