Newly spotted comet may outshine the full moon: In +/- 12 months

21:57 25 September 2012

Jeff Hecht, contributor

C2012S1_2012Sep22_H06.jpg

(Image: E. Guido, G. Sostero, N. Howes)

Today, the newfound comet seen above is just a tiny dot in the sky beyond Jupiter. But in about a year, it might be one of the brightest objects in our night sky.

Vitali Nevski and Artyom Novichonok, of the International Scientific Optical Network (ISON) in Russia, discovered comet C/2012 S1 (ISON) on 21 September via images taken with a 40-centimetre reflecting telescope. Other sky-watchers soon spotted it, and the International Astronomical Union’s Minor Planet Center in Cambridge, Massachusetts, announced the find yesterday.

From the combined observations, astronomers were able to trace the comet’s recent path and find images of it dating back to late December 2011. From there they calculated a near-parabolic orbit that has comet ISON headed almost straight towards the sun.

Astronomers at the Remanzacco Observatory in Italy think that ISON will skim less than 1.4 million kilometres from the sun’s surface on 28 or 29 November.

The comet’s orbit also suggests it is a newcomer fresh from the Oort cloud, a distant halo of icy objects that surrounds the solar system. We last had a visitor direct from the cloud in 2009, when the green comet Lulin swooped in and sprouted two tails.

As with Lulin, the intense heat of ISON’s solar fly-by should vaporise the comet’s hard shell of pristine ices, releasing trapped dust that would help it grow an exceptionally bright tail. Astronomy Now magazine reports that comet ISON could even be brighter than the full moon around its closest approach to the sun.

Skirting our star means that, to viewers on Earth, the comet will appear close to the horizon and to the sun’s glare, making it difficult to see at first. ISON will fade but become easier to spot as it heads back towards the outer solar system. By 9 December it should be about as bright as Polaris, the North Star, according to Remanzacco Observatory astronomers. ISON should continue to be visible to the unaided eye until mid-January 2014.

But veteran astronomers warn that fresh comets with orbits that almost skim the sun are notoriously unpredictable. Results can range from the spectacular comet McNaught of January 2007 to the infamously fizzled comet Kohoutek of 1973.