Comet chasing space probe will reach target Wednesday after 6 billion km dash

Chase over 6 billion km to end on Wednesday when European Space Agency probe Rosetta is set to land laboratory on a galactic wanderer

PUBLISHED : Sunday, 03 August, 2014, 11:20am
UPDATED : Monday, 04 August, 2014, 8:37am


After a decade-long quest spanning six billion kilometres, this week a European space probe will intercept a comet, one of the solar system's enigmatic wanderers.

The moment on Wednesday will mark a key phase of the most ambitious project undertaken by the European Space Agency (ESA), a €1.3 billion (HK$13.5 billion) bid to get to know these timeless space rovers.

More than 400 million km from where it was launched in March 2004, the spacecraft Rosetta will finally meet up with Comet 67P/Churyumov-Gerasimenko (C-G).

To get there, Rosetta has had to make four passes of Mars and Earth, using their gravitational force as a slingshot to build up speed, and then entering a 31-month hibernation as light from the sun became too weak for its solar panels.

It was awakened in January.

After braking manoeuvres, the three-tonne craft should move about 100km from the comet, a navigational feat that, if all goes well, will be followed by glittering scientific rewards.

"It has taken more than 10 years to get here," said Sylvain Lodiot, spacecraft operations manager. "Now we have to learn how to dock with the comet, and stay with it for the research months ahead."

Astrophysicists believe comets are clusters of the oldest dust and ice found in the solar system, the rubble left from the formation of the planets 4.6 billion years ago.

Some suggest they could be the key to understanding how the planets coalesced after the sun flared into life.

One theory is that comets, by bombarding the fledgling earth, helped kick-start life by bringing water and organic molecules.

Until now, though, explorations of comets have been rare and mainly entailed fly-bys by probes on unrelated missions snatching pictures from thousands of kilometres away.

Exceptions were the US probe Stardust, which recovered dust snatched from a comet's wake, while Europe's Giotto ventured to within 200km of a comet's surface.

On November 11, the plan is for Rosetta to move to within a few kilometres of the comet to send down a 100kg refrigerator-sized robot laboratory known as Philae.

Anchored to the surface, Philae will carry out experiments in cometary chemistry and texture for up to six months. After the lander expires, Rosetta will accompany "C-G" as it passes around the sun and heads out towards the orbit of Jupiter.

Before November's landing, though, Rosetta's operators have a mountain of work to do.

The first few weeks will be a get-to-know-you exercise, as the spacecraft gingerly carries out elongated loops around the comet, scanning its surface.

Last month, as Rosetta moved closer to the comet, its cameras revealed that the target body, far from being shaped like a potato as many had expected, rather resembled a duck.

It has two lobes, one big and the other small, connected by a "neck".The unexpected shape would limit the choice of a landing site, Philippe Lamy of the Astrophysics Laboratory of Marseilles, France, said. "You can reasonably argue that it will impose additional constraints."


Facts and figures about comets

  • Comets are bodies of ancient ice and dust that orbit the sun and are believed to be almost pristine material left over from the solar system's formation 4.6 billion years ago.
  • As a comet nears the sun, some of the ice melts and transforms into gusts of gas, the bright "coma" around its head. The gassy wake, and dust loosened by the melting ice, creates a spectacular tail that is reflected in the sun's rays and may stretch across millions of kilometres in space. The word for comet comes from stella cometa, Latin for "long-haired star".
  • Like solar eclipses, comets have been associated with great events of history, good and bad. The birth of Jesus and Napoleon, the eruption of Vesuvius in 79AD that destroyed Pompeii, and the Great Plague of 1665 that ravaged London have been linked to comets.
  • About 2,000 comets have been observed and recorded over the past 2,500 years. They follow elliptical orbits, with a return taking anything from a few years to as many as 40,000 years. Some scientists estimate there could be billions of comets, only a tiny fraction of which have been seen.
  • The most famous of our comets is named after British astronomer Edmond Halley, who was the first to prove that the space objects orbit the sun and return regularly. He showed that a comet of 1682, now called Halley's Comet, was identical with two that had appeared in 1607 and 1531, and he successfully predicted the comet's next return, which occurred in 1758, 16 years after his death. Halley's Comet last passed earth in 1986.
  • Comet 67P/Churyumov-Gerasimenko, the target of the Rosetta space probe, is named after Soviet astronomers Klim Churyumov and Svetlana Gerasimenko, who first identified it, separately, in 1969.

Agence France-Presse