Astronomers : Comet, Thought Dead but Found Alive, Is Now Fading Away : worldleaks
A comet that once predicted to light up the night skies — then all but vanished, and later seemed to blaze back to life is now fading away, astronomers say.
“I think for the most part it’s dead,” said C. Alex Young, the associate director for science in the heliophysics division at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The folks are finally pretty confident that’s the case.”
En route to its death, the comet, ISON, has provided one twist after another. On Thursday, when it made its nearest approach to the sun, the comet escaped observation, and scientists resolved that it had disintegrated and vaporized.
Then, a few hours later, it reappeared. A bright spot at the head of the comet proposed that part of its icy nucleus had lived.
But the resurrection was short-lived. ISON faded again over the weekend. By Sunday, it was already so dim that its debris will no longer be visible to the naked eye when it passes through Earth’s region this month.
“I really don’t think there’s a whole lot left,” said Karl Battams, an astrophysicist at the Naval Research Laboratory who has spent a week observing ISON at the Kitt Peak National Observatory in Arizona. “I’m very disappointed for the public, because we’re not going to see this beautiful object in the Northern Hemisphere skies.”
Dr. Battams said the comet had probably fallen largely apart before its closest approach to the sun.
He said it was difficult to tell what was seen moving away from the sun. The comet may have possessed a small nucleus that has since vaporized. Or the ice that holds it together had already vaporized, leaving just a loose pile of rubble.
“It’s also possible it was just a cloud of dust at that point,” Dr. Battams said.
The comet, discovered in September 2012 while still beyond Jupiter’s orbit, initiated from the Oort cloud, a region of icy debris over a light-year from the sun.
For scientists, the excitement of observation is over, but the work of studying data to understand what happened will take weeks and months. The complete disintegration of ISON could give better information about its composition — and hints of how the planets formed — than if it had stayed intact.
“Scientifically, I don’t know if it gets much better than seeing the comet being ripped apart, falling apart right before your eyes,” Dr. Battams said.
For more articles : www.worldleaks.com