Sun, Nov 09, 2014 - Page 6 News List

Science lifts veil on comets as probe nears goal

AFP, PARIS

An artist’s impression shows Rosetta’s lander, Philae, on the surface of Comet 67P/Churyumov-Gerasimenko.

Photo: AFP

For millennia, the sight of a comet filled humans with awe or dread.

The birth of Jesus, the assassination of Julius Caesar, the Great Plague of London, the coming of war or peace, bountiful harvests or famine... all were thought to be portended by cosmic heralds.

Bit by bit, mysticism about comets has been replaced by fact as scientists discover more about these epic and ancient travelers of the skies.

As it turns out, comets might be more extraordinary than even the deepest superstition could imagine.

They might have even brought life to our planet, according to some theories.

For decades, astrophysicists have debated whether, at the dawn of our Solar System, comets peppered Earth with some of the chemical essentials for life as we know it.

The answer may be within reach.

On Wednesday, a European robotic lab, Philae, aims to make the first landing on a comet. It is to carry out experiments on the comet as the pair hurtle toward the sun, escorted by Philae’s comet-orbiting carrier, Rosetta.

“Comets are the most ancient objects in the solar system,” Francis Rocard of France’s National Centre for Space Studies (CNES) said. “We want to know if comets played a part in providing Earth with water and carbon. There is no doubt that the results from Rosetta and Philae will shake up what we know.”

Dubbed “dirty snowballs” by US astronomer Fred Whipple, comets are deemed to be clusters of primeval carbon and ice, typically a few kilometers across.

Blacker than coal, they were formed shortly after the sun flared into life in a halo of dust and gas — the stuff that eventually formed the planets and other bodies.

Today, the solar system is considered a pretty quiet place, compared with 4.6 billion years ago, when it was a shooting gallery.

The nascent Earth would have been repeatedly whacked by comets and asteroids, swelling the planet and depositing ice, which in some theories became today’s oceans.

“This would have created a wonderful culture medium — a liquid enabling highly rich carbon material to react and create prebiotic chemistry,” Rocard said.

“It would have led to the first membranes and ultimately the first cells — life itself,” he said.

The key to confirming this theory lies in the ratio of hydrogen and deuterium on the comet, which Rosetta and Philae will measure with their instruments, to be compared to the chemical make-up of water on Earth.

Doomed to orbit the Sun in elliptical circuits, comets undergo thermal and gravity stress as they near the star.

Some of their ice is transformed into gusts of gas, the bright “coma” around a comet’s head.

The gassy wake, and dust loosened by the melting ice, create a spectacular tail reflected in the sun’s rays that might stretch across millions of kilometers. The word for comet comes from stella cometa — Latin for “long-haired star.”

The best-known is Halley’s comet, named after 17th-century English astronomer Edmond Halley, who was the first to show that comets orbit the Sun and return regularly. Just over 5,000 comets have been observed since the first recorded sighting by Chinese skygazers in about 240 BC.

However, some experts believe there could be as many as 1 trillion out there, the European Space Agency says.

“Short period” comets take less than 200 years to orbit. They are thought to return to the Kuiper Belt, just beyond the orbit of Neptune.

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