Is the ‘Christmas Comet’ actually cracking up?

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 amateur Russian astronomers, Vitaly Nevski and Artyom Novichonok, on Sep 21, 2012.

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 towards the end of the year — a timing that gave it the tabloid title of “Christmas Comet” or even “Comet of the Century”. But fears are multiplying that the great show will be cancelled.

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. 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,” said Ferrin.

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

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

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