Come October, the Earth will have a date with a visitor from the outer reaches of the solar system. Comet Elenin, discovered last December, will pay us a flying visit, much to the excitement of the global astronomer community.

But, the intrepid visitor from the fringes is in the news for all the wrong reasons. Like many comets in the past, Elenin too has become fodder for doomsday cannons. Since the time of its visit is close to the “appointed” date of the 2012 doomsday prophecy, the comet is being forced to assume a villainous role by conspiracy theorists. One of the many theories about the 2012 apocalypse says a passing planet called Nibiru will collide with the earth, marking its end on December 21, 2012!

A team of scientists from the US National Aeronautics and Space Administration (Nasa) not only debunked these cataclysmic theories, but also spent several months studying the astral visitor so that they can answer the unfounded concerns pinned on it. They say that the comet, which is much smaller and dimmer than many others that have passed by the Earth in the last several decades, will not get closer than 35 million kilometres, that is, 90 times the distance to the moon. At such a distance, the comet is not expected to have much influence on Earth when it comes closest to our home planet on October 16 this year.

“Comet Elenin will not only be far away, it is also on the smaller side for comets,” says Don Yeomans of Nasa’s Jet Propulsion Laboratory in California, who along with Nasa astrobiologist David Morrison has been studying the comet.

Discovered by the Russian astronomer Leonid Elenin on December 10, 2010, Comet Elenin is not expected to put up a dazzling display. When first detected, it was about 647 million kilometres away from the earth. Recently, the comet came within 7 million kilometres of a Nasa space probe tracking the sun.

“We don’t yet know if Comet Elenin will be visible to the naked eye when it’s closer to Earth,” says Morrison. “At the rate it is going, seeing the comet at its best in early October will require binoculars and a very dark sky.”

A comet is a celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing. It derives its name from a visible coma (a thin, fuzzy, temporary atmosphere) formed around its nucleus when it gets close enough to the sun.

Comets originate from two sources in the outer reaches of the solar system — the Oort Cloud and the Kuiper Belt. Long-period comets, which take 200 or more years to orbit the sun, are from the Oort Cloud, whereas the short-period ones emerge from the Kuiper belt

Usually, the dimensions of the nucleus of a comet range from a few hundred metres to tens of kilometres, but their coma can be much larger. “In some comets, the coma can be even larger than the sun,” says Samir Dhurde, an astronomer specialising in public outreach at the Inter-University Centre for Astronomy and Astrophysics in Pune. Similarly, its tail can also be very long — sometimes as long as several tens of millions kilometres. For instance, the tail of the Halley’s Comet on its last flyby the Earth in 1986 was 50 million kilometres, says Dhurde. Comet Elenin’s tail is said to be about a million kilometres long.

This length doesn’t mean anything as each kilometre of the tail contains only a few hundred thousand molecules of dust and frozen gas. “If you condense the entire 100 thousand kilometre long tail of a comet to the density of water, it would not even fill a swimming pool,” says Dhurde.

Yeomans doesn’t expect Comet Elenin to put on any great show, unlike Comet Hale-Bopp, which was visible in 1997. Comet Hale-Bopp was one of the brightest comets to pass the earth in several decades, says Morrison.

Comets shine because the dust particles they contain reflect sunlight directly and the gases glow from ionisation, says Dhurde.

One of the reasons why the Nasa scientists are putting in a lot of effort to educate the public about Comet Elenin is because of the unfortunate things that had occurred during the sighting of Comet Hale-Bopp. Nearly 40 members of a US-based religious sect called Heaven’s Gate committed suicide on March 26, 1997, in order to reach an imaginary alien aircraft which they thought was following the comet. They believed that Earth was to be recycled and hence their only chance to survive was to leave it immediately by getting onto the spaceship!

One of the theories being floated about Comet Elenin by doomsday theorists is that its alignment with other celestial bodies would have disastrous consequences for Earth. “Any approximate alignment of Comet Elenin with other celestial bodies is meaningless, nor will it influence us in any way here on Earth,” says Yeomans.

This modest-sized icy dirtball will, in fact, have no measureable influence on the planet. “My subcompact automobile exerts a greater influence on the ocean’s tides than Comet Elenin ever will,” jokes Yeomans.

Several new comets are discovered every year. Normally we do not hear about them as they are small and faint. Comet Elenin too belongs to this category. But it received more attention that it deserves because of misguiding Internet postings about its influence on future of the Earth, the Nasa researchers say.

According to Dhurde, Elenin is of interest to scientists because it is a new comet. It is on the rounds of the inner solar system and has not been observed before. “This was either because it was faint or it came last years ago when humans were not equipped to see faint objects,” he says. A study of its tails and coma will give information about the conditions and composition of the outer solar system where it came from.

“However, it is difficult to say if it will be a bright ‘great comet’ or will dimly fizzle. Be prepared for disappointment,” warns Dhurde.

So don’t stay up to see it.