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Comet of the Century? - presented by Science@NASA
Out near the orbit of Jupiter,
a faint speck of light is moving through the black of space.
At first glance it doesn't look like much,
no brighter than a thousand distant stars speckling the velvet sky behind it;
indeed, it takes a big telescope to make out that it is a comet.
But what a comet it could turn out to be....
Later this year,
"Comet ISON" could blossom into a striking naked eye object
visible even in broad daylight.
'Comet ISON is a sungrazer,'
explains Karl Battams of the Naval Research Lab.
'The orbit of the comet will bring it very close to the sun,
which we know can be a spectacular thing.'
Russian astronomers Vitali Nevski and Artyom Novichonok
found the comet in Sept. 2012.
It bears the name of their night-sky survey program,
the International Scientific Optical Network, or 'ISON.'
As 2013 unfolds,
the comet is still very far away-near the orbit of Jupiter.
That's why it looks like a speck.
'But for an object at such extreme distance,
it is actually very bright,' says Battams.
The comet's glow suggests that is spewing gas and dust
from a fairly large nucleus-
'in the 1 to 10 km range,'
estimates Matthew Knight of the Lowell Observatory.
On Nov. 28, 2013,
this 'dirty snowball' will fly through the sun's atmosphere
little more than a million km from the stellar surface.
If the comet survives--a big IF--
it could emerge glowing as brightly as the Moon,
briefly visible near the sun in broad daylight.
The comet's dusty tail stretching into the night sky
could create a worldwide sensation.
Some reporters have started calling ISON the 'Comet of the Century,'
but Don Yeomans of NASA Near-Earth Object Program
thinks that's premature.
'I'm old enough to remember the last 'Comet of the Century',' he says.
In 1973, a distant comet named Kohoutek
looked like it would put on a great show,
much like ISON.
The actual apparition was such a let-down
that Johnny Carson made jokes about it on the Tonight Show.
'It fizzled,' says Yeomans.
'Comets are notoriously unpredictable.'
'Comet ISON has the potential to live up to the hype,
but it also has the potential to do nothing,' agrees Battams.
One hazard is the sun.
Solar radiation can affect a comet’s trajectory
and gravitational effects have been known to destroy comets.
A recent example is Comet Elenin,
which broke apart and dissipated in 2011 as it approached the sun.
Elenin, however, was a much smaller comet.
A better comparison, perhaps,
is Comet Lovejoy, which flew through the sun's atmosphere in 2011.
Lovejoy emerged intact
and wowed observers with a garish tail for weeks.
'Comet ISON is at least twice as big as Comet Lovejoy,' notes Knight.
This would seem to favor Comet ISON surviving
and ultimately putting on a good show.
One of the most exciting possibilities would be a partial break-up.
'If Comet ISON splits,
it might appear as a 'string of pearls'
when viewed through a telescope,' speculates Battams.
'It might even resemble the famous Comet Shoemaker-Levy 9
that hit Jupiter in 1994.'
A break-up would pose no threat to Earth, assures Yeomans.
'Comet ISON is not on a collision course.
If it breaks up,
the fragments would continue along the same safe trajectory
as the original comet.'
Whatever happens,
northern sky watchers will get a good view.
For months after it swings by the sun,
Comet ISON will be well placed for observers in the northern hemisphere.
It will pass almost directly over the North Pole,
making it a circumpolar object visible all night long.
Will Comet ISON fizzle ... or sizzle?
The answer will be plain to see.
For more news about Comet ISON,
and other visitors from deep space,
stay tuned to science.nasa.gov.