Sun, Oct 20, 2013 - Page 6 News List

‘Christmas Comet’ could break up and fizzle out: scientists

AFP, PARIS

An incoming comet that skygazers had hoped would provide one of the greatest celestial shows of the century could be a fizzle.

So say astronomers tracking the eagerly awaited Comet ISON as it races to a searing encounter with the sun.

Formally known as C/2012 S1 (ISON), the comet was spotted by a pair of hard-working amateur Russian astronomers, Vitaly Nevski and Artyom Novichonok, on Sept. 21 last year.

It is called ISON because they used a telescope called the International Scientific Optical Network near Kislovodsk, in the northern Caucasus.

After the discovery was validated by the International Astronomical Union (IAU), interest in the enigmatic wanderer became huge.

Calculations showed that after looping around the sun, the comet would become a blaze of glory toward the end of the year — a timing that gave it the tabloid title of “Christmas Comet” or even “Comet of the Century.”

However, fears are multiplying that the great show will be canceled.

Light signatures from ISON, which has just streaked past Mars, indicate the comet is about to break up, says Ignacio Ferrin, an astrophysicist at the University of Antioquia in Medellin, Colombia.

“This disintegration will take place before it reaches perihelion,” Ferrin said in an e-mail.

Perihelion is an orbit’s closest point to the Sun, which ISON is supposed to reach on Nov. 28.

“There are also predictions for disintegration at perihelion, but based on the evidence, the comet will not get there,” Ferrin said.

He said that comets typically brighten as they get closer to the sun, crossing a temperature threshold that causes their icy surfaces to evaporate, depositing water vapor, other gases and dust in their wake.

However, the light curve from ISON slowed down and then remained practically constant, with no sign of greater brightness, as it raced forward, Ferrin said.

This is a signature that matches four previous comets that have broken up catastrophically, he said.

“Comets in general appear to be quite fragile, and are observed to fragment or split,” said Duncan Steel, a visiting astronomer at Armagh Observatory in Northern Ireland. “It has always been a good bet that ISON would do this, and there is now evidence that this may be now occurring.”

Comets are believed to be huge clusters of primeval dust and frozen ices, including water and organic molecules that, some say, delivered the building blocks of life to the infant Earth.

Doomed to orbit the sun in periods that can range from years to many millennia, comets undergo thermal stress as they near the star.

Veterans that make short-period flybys, such as Halley’s Comet, appear to have a crust of silicates and “tarry” carbon molecules to insulate them from the heat.

However, rare visitors such as ISON have no such protection, Steel said.

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