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 The moment of truth comes Thursday — Thanksgiving Day.
The sun-grazing Comet ISON, now thought to be less than a mile wide,
will either fry and shatter, victim of the sun's incredible power,
or endure and quite possibly put on one fabulous celestial show.
Talk about an astronomical cliffhanger.
Even the smartest scientists are reluctant to lay odds.
Should it survive, ISON, pronounced EYE'-sahn, would be visible with
the naked eye through December, at least from the Northern
Hemisphere. Discernible at times in November with ordinary
binoculars and occasionally even just the naked eye, it already has
dazzled observers and is considered the most scrutinized comet ever
by NASA. But the best is, potentially, yet to come.
Detected just over a year ago, the comet is passing through the
inner solar system for the first time. Still fresh, this comet is
thought to bear the pristine matter of the beginning of our solar
system.
It's believed to be straight from the Oort cloud on the fringes of
the solar system, home to countless icy bodies, most notably the
frozen balls of dust and gas in orbit around the sun known as
comets. For whatever reason, ISON was propelled out of this cloud
and drawn toward the heart of the solar system by the sun's intense
gravitational pull.
The closer the comet gets to the sun, the faster it gets.
In January, it was clocked at 40,000 mph.
By last Thursday, with just a week to go, it had accelerated to
150,000 mph.
Right around the time many Americans will be feasting on turkey, the
comet will zip within 730,000 miles of the sun, less than the actual
solar diameter. In other words, another sun wouldn't fit in the
missed distance.
By the time ISON slingshots around the sun, it will be moving at a
mind-boggling 828,000 mph.
Whether it survives or is torn apart, earthlings have nothing to
fear.
The comet will venture no closer to us than about 40 million miles,
less than half the distance between Earth and the sun. That closest
approach to Earth will occur Dec. 26. Then it will head away in the
opposite direction forever, given its anticipated trajectory once it
flies by the sun.
ISON is named after the International Scientific Optical Network,
used by a pair of Russian astronomers to detect the comet in
September last year. But it officially is known as C/2012 S1, a
designation indicating when it was discovered.
Take heart: The "C'' means it is not expected here again.
NASA wasted no time jumping on ISON. The space agency's Deep Impact
spacecraft observed ISON back in January from a distance of about
500 million miles.
Since then, the observations have stacked up.
Among NASA's space telescopes taking a look: Swift, Hubble, Spitzer,
Mars Reconnaissance Orbiter, Solar and Heliospheric Observatory or
SOHO, Chandra, Mercury-orbiting Messenger, and the Stereo twin
spacecraft.
"Every spacecraft that has a camera, we're turning on it," said John
Grunsfeld, NASA's science mission director.
The newly launched Maven spacecraft en route to Mars will gaze at
ISON the second week of December, once its ultraviolet instrument is
up and running.
"That's well after closest approach to the sun," the University of
Colorado's Nick Schneider, who's in charge of the instrument, said
in an email. So it's not known "whether we'll see a comet, comet
bits or the last wisps of comet vapor."
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"Whatever happens, it's bound to be interesting. The quip from my
colleagues is, 'Comets are like cats: They have tails and do
whatever they want.'"
Besides ISON, NASA is spying on Comet Siding Spring, another Oort
cloud comet discovered in January by the Australian observatory of
the same name. Siding Spring will pass within tens of thousands of
miles of Mars next October, so close that scientists believe the
coma of the comet — its thin but expansive atmosphere — will envelop
the red planet.
"It will be blanketed in water and dust and meteorites. It moves
like 50 kilometers per second, blazing through the environment,"
said Jim Green, director of NASA's planetary science division.
That's more than 110,000 mph, so the comet will be gone from Mars
"pretty quick."
Siding Spring-type events have happened before, Green noted. "We're
just lucky in our lifetime" to have the right spacecraft in the
right place to observe the spectacle.
The same applies to ISON.
Add small sounding rockets to the list of paparazzi chasing the
comet; NASA fired up one from New Mexico on Wednesday with an
ultraviolet telescope that reached 172 miles high before descending
by parachute. Consider all the ground observatories peering at the
comet, as well as countless amateur astronomers and
astrophotographers, and ISON has become the belle of the cosmic
ball.
"Comets evolve from the time they start brightening until they go
all the way around the sun, and go back out," Green said. "By having
and leveraging these assets, it really gives us that view — that
unique view — that we couldn't get otherwise."
Some sky gazers speculated early on that ISON might become the comet
of the century because of its brightness, although expectations have
dimmed over the past year.
Scientists expect to know ISON's fate fairly quickly. At least three
spacecraft will be aiming that way in real time.
If ISON survives, "it's going to fly right over the Northern
Hemisphere," Green said with clear excitement in his voice. It
should be visible with the naked eye for 30 days.
"So it's really a holiday comet. You ought to be able to see it well
past Christmas," Green said. "But it's got to survive it, that's the
only thing about that."
___
Online:
NASA: http://www.nasa.gov/ison/
ISON Observing Campaign:
http://www.isoncampaign.org/
[Associated
Press; MARCIA DUNN, AP Aerospace Writer]
Copyright 2013 The Associated
Press. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
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