By Irene Klotz
CAPE CANAVERAL, Fla., Nov 29 (Reuters) - A smaller, paler version of Comet ISON may have survived incineration in the sun's corona and may be brightening, scientists said on Friday.
Since its discovery in September 2012, Comet ISON has been full of surprises. It started off extremely bright, considering its great distance from the sun at the time, beyond Jupiter's orbit.
As it drew closer, it did not brighten as much as expected, raising doubts about its size and the amount of water it contained. Ice in a comet's body vaporizes from solar heating, causing a bright stream of particles to trail the body in a distinctive tail.
Conflicting pictures of the comet's future continued until Thursday when ISON apparently flew too close to the sun. Its long tail and nucleus seemingly vaporized in the solar furnace, dashing hopes of a naked-eye comet visible in Earth's skies in December.
But late on Thursday, ISON surprised again.
"A bright streak of material streaming away from the sun appeared in the European Space Agency and NASA's Solar and Heliospheric Observatory later in the evening," NASA wrote on its website on Friday.
"The question remains whether it is merely debris from the comet, or if some portion of the comet's nucleus survived," the U.S. space agency said.
Preliminary analysis suggests that at least a small nucleus is intact.
"One could almost be forgiven for thinking that there's a comet in the images," astrophysicist Karl Battams, with the Naval Research Laboratory in Washington, wrote in a blog posted Thursday night.
"Right now it does appear that a least some small fraction of ISON has remained in one piece and is actively releasing material," Battams wrote.
"If there is a nucleus, it is still too soon to tell how long it will survive. If it does survive for more than a few days, it is too soon to tell if the comet will be visible in the night sky. If it is visible in the night sky, it is too soon to say how bright it will be ... I think you get the picture, yes?" he added.
The comet was discovered last year by two amateur astronomers using Russia's International Scientific Optical Network, or ISON.
Comets are believed to be frozen remains left over from the formation of the solar system some 4.5 billion years ago.
The family of comets that ISON is from resides in the Oort Cloud, which is about 10,000 times farther away from the sun than Earth, halfway to the next star.
Computer models show it left the outer edge of the solar system about 5.5 million years ago and began journeying toward the sun.
At its closest approach on Thursday, it passed just 730,000 miles (1.2 million km) from the sun's surface and experienced temperatures reaching 5,000 degrees Fahrenheit (2,760 degrees Celsius.)
"This has unquestionably been the most extraordinary comet that ... I, and many other astronomers, have ever witnessed," Battams wrote. "This story isn't over yet."
(Reporting by Irene Klotz; Editing by Jane Sutton and Paul Simao)
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