(Comet ISON, imaged by longtime amateur astrophotograper Damian Peach in the U.K. He used a 4-inch f/5 telescope for 12 minutes of combined exposures on November 15th. Credit: Damian Peach / SkyandTelescope.com)
Astronomers keeping a close eye on the highly-anticipated Comet ISON, are reporting that ‘something’ is happening to the icy visitor as it quickly plummets towards the sun.
And it may, or may not, be bad news for skywatchers.
What has comet scientists puzzled about Comet ISON’s fate are the latest observations, which show a dramatic drop in the comet’s emissions of hydrogen cyanide gas. The gas is thought to normally hide in pockets beneath the comet’s nucleus surface. When the surface ice boils off as the comet approaches the sun, the gas is released into space and the comet develops a tail.
However, for some reason these emissions appear to have declined significantly from Comet ISON in the past week or so. That may be an ominous hint that enough ice has vaporized, due to the increasingly-intense solar heat, that the comet’s frozen 1.2-mile-wide (2 kilometer) nucleus has started to fracture and disintegrate.
Watch Comet ISON
Is there still a chance Comet ISON will survive its encounter with the sun on Thursday, November 28th and become a great sky show in December? You bet!
Astronomers have definitely not written off the comet yet, noting that comets historically have behaved in unpredictable fashion, and what we are witnessing now is an unprecedented astronomical event, the likes of which has never been observed in such detail. during a NASA news briefing on November 26th NASA scientists gave ISON up to 40% chance of surviving and said, even if the nucleus does break up it may still give the general public quite a sky show early December with a long sweeping tail visible.
Karl Battams, a comet scientist with the U.S. Naval Research Laboratory in Washington, D.C. who blogs on NASA’s Comet ISON Observing Campaign website put it this way on Monday, “Comet ISON is a dynamically new sungrazing comet, fresh in from the Oort Cloud, and the last time we saw an object like this was never! Furthermore, a sungrazing comet just three days from perihelion [closest approach to the sun] has never been studied in this kind of detail—we’re breaking new ground here! When we factor in your standard ‘comets are unpredictable’ disclaimer, what we have is a huge recipe for the unknown.”
One thing we know for sure is that when Comet ISON reaches perihelion on US Thanksgiving Day, it will be flying right through the hellish outer atmosphere of the sun—missing its searing surface by only 684,000 miles (1.1 million kilometers). That is a little less than only two and a half times the distance from Earth to the moon.
(At its closest point to the sun Comet ISON will be about 1.1 million km from its surface. Credit: NASA)
NASA will host a live Google+ Hangout with comet experts on November 28 from 1 pm to 3:30 pm EST (18:30–20:00 UT)—at exactly the time ISON slingshots around the sun. Dubbed ‘Fire vs. ISON – the Epic Battle Live‘, the online event will give the public a chance to watch, ask questions of scientists, and track the comet live through streaming images beamed back from NASA’s Solar Dynamics Observatory (SDO) spacecraft, which is watching ISON’s closest approach to the sun.
If it manages to survive its roasting, the comet could still become an impressive naked-eye comet with a long tail in the pre-dawn sky. Or it could become just a faint smudge in binoculars.
In any case, sky-watchers around the world are gearing up for the chance to catch sight of Comet ISON. In the best-case scenario that it does round the sun intact, observers should start scanning the very low eastern morning skies about an half hour to an hour before local sunrise starting Sunday, December 1, for a view of the comet in the glare of twilight. Every day thereafter the comet moves a bit higher in the morning sky as it treks farther away from the sun and back towards the outer solar system.
The moment of truth for Comet ISON has arrived and it’s a nail-bitter for sure. Will it dazzle or fizzle? Time will tell and no doubt the world is watching.
Courtesy : National Geographic