Tuesday, November 26, 2013

Is Comet ISON disintegrating?

There has talk for some days about whether Comet ISON has fragmented. The sungrazing comet experts were saying no, but Monday morning Karl Battams – one of the great communicators at NASA’s Comet ISON Observing Campaign website – said that something is happening to the comet. There are signs it may be fragmenting. He wrote:

    There’s evidence that ISON’s nucleus might not be holding up well (by which I mean falling apart!) It was always a possibility…we’ll see!

Later, he added:

    It is absolutely conceivable that ISON remains in one piece, and is just being a sungrazer.

In other words, the word isn’t in yet on whether ISON is still intact.

The evidence for ISON’s possible disintegration comes in the form of a rapid drop in emissions, in recent days, from a certain kind of molecule (hydrogen cyanide molecule) known to be embedded in cometary ice. At his Bad Astronomy blog on Slate, Phil Plait explained that it’s the ice of a comet like ISON that holds the comet together. ISON is full of fresh ice. It’s a first-time visitor from the Oort comet cloud surrounding our solar system. If enough ice boils off the comet as it gets closer to the sun, the comet will literally fall apart.

But how much ice has ISON lost? Enough so that the comet will fall apart? Meanwhile, dust has also been observed to be pouring from the comet. These signs could mean that ISON’s nucleus has completely disrupted. Or not.

Why don’t astronomers know what will happen? Karl Battams explained:

    … these reports are new, and while they are undoubtedly valid, we do still need to keep observing the comet to be sure what it happening. Remember: 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 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.

We do know that, after traveling at least a million years from the Oort Cloud, Comet ISON is now plummeting fast toward the sun. Its perihelion or closest point to the sun will be on November 28 – Thanksgiving Day in the U.S. At perihelion, the comet will be traveling at 248 miles per second, encountering solar temperatures of up to 5,000 degrees Fahrenheit.

Thus this week will bring Comet ISON’s moment of truth, its day of reckoning. The comet is close to the sun on our sky’s dome now and won’t be seen from Earth this week except, perhaps, by a few experienced observers. However, NASA and ESA’s fleet of sun-observing spacecraft will be watching it.

If it survives its passage near the sun, Comet ISON will return to our skies in early December, and, indeed, early December may be the best time to try to see the comet … if there is a comet left to see.

Courtesy - earthsky.org

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