For months, all eyes in the sky have pointed at the comet that's zooming toward a blisteringly close encounter with the sun.
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."
"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."
