Comet of the century?

NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team

On September 2nd, 2012, two Russian astronomers discovered a comet designated as C/2012 S1 ISON. When the orbit was calculated, astronomers realized that the object would pass at only 1.3 solar radii from the Sun on November 28th, 2013. Numerous press articles contended that the object would be as bright as the full Moon and that in fact it could become “the comet of the century”.

Dr. Ignacio Ferrin, Astronomer from the Institute of Physics of the University of Antioquia, in Medellín, Colombia, has concluded a study of the comet, using the latest observations available. Dr. Ferrin is a researcher and Faculty Member in the Astronomy Program of that Institute. He is a recognized cometary specialist.

“Comet ISON has presented a peculiar behavior”, said Dr. Ferrín. “The light curve has exhibited a “slowdown event” characterized by a constant brightness with no indication of a brightness increase tendency. This slowdown took place around January 13th, 2013. For 132 days after that date and up to the last available observation, the brightness has remained constant”. Thus the astronomer concludes that it is highly unlikely that the comet will be as bright as the full Moon.

This peculiar behavior could possibly be explained if the comet were water deficient, or if a surface layer of rock or non-volatile silicate dust were quenching the sublimation to space.

The strange behavior of comet ISON is reminiscent of what happened to comet C/2002 O4 Hönig who remained with the same brightness for 52 days, after which it disintegrated with no observable residue. It is to be noticed that comet ISON has been in that state for much longer, 132 days and counting. However astronomers do not know what is the current status of the comet, since it has entered the solar glare and it is unobservable.

Orbit diagram of Comet ISON. Credit: JPL Near-Earth Object Program

Even if the comet survives this scenario it will have to surpass other difficulties. The comet will reach perihelion very near the Sun, where the astronomers have calculated a temperature of 2700 degrees celsius, sufficient to melt iron and lead. Besides this trial by fire, the comet will penetrate Roche’s Limit. Any object that penetrates this forbidden limit will experience solar gravitational forces that may tear apart the nucleus of the comet. The combination of temperature, radiation and tidal forces below the Roche’s Limit, may prove too much for the comet, who may not survive the encounter with the Sun.

There is a brief window of observation between October 7th and November 4th, when the comet will be more than 50 degrees from the Sun. The scientist add that even so the observational conditions will be difficult to determine what was the fate of the comet.

“The future of comet ISON does not look bright”, Dr. Ferrin conclude.

Many astrobiologists believe that comets could have played a key role in the origin of life by delivering water and other important molecules for living cells to the early Earth. As comets make their way through the inner Solar System, it gives scientists a chance to observe them and study their behavoir and compositions.

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