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."
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