ISON is small but it will be well
observed will flash into maximum visibility almost immediately as it leaves the
sun. The size suggests that it will not
break up that easily.
We now know that the gas tail is
strongly emitting carbon dioxide as part of the mix and this conforms to my
conjecture that the bulk of the dust is charged elemental carbon. At least this time we will collect plenty of
measurements to help fill in all the blanks in our knowledge.
I noticed independent claims out
there that Mars has somehow gained a halo from the passing tail. Whatever that presently means it is
noteworthy that another comet now coming in is expected to share it tail with
Mars in a few months.
Astronomers increasingly
excited as Comet ISON accelerates toward fateful rendezvous with the sun
MARCIA
DUNN
CAPE CANAVERAL, Fla. — The
Associated Press
Published Monday, Nov. 25 2013,
9:53 AM EST
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 – U.S. 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.
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 vapour.”
“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 kilometres 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.”
Comet Nears Sun, Offering Planetary Clues
NASA
Published:
November 26, 2013
A comet that spent the first 4.5 billion years of its existence in
the farthest reaches of the solar system will almost graze the furnace of the
sun on Thursday.
Comet ISON’s close approach — and its possible
demise, from the sun’s heat and gravitational forces — will give scientists an
unprecedented look at the ingredients that came together to form the planets.
“It’s a dinosaur bone of solar system
formation,” said Carey M. Lisse, a senior research scientist at the Applied
Physics Laboratory at Johns Hopkins University, during a NASA news conference
on Tuesday.
If the comet survives — though many experts like
Dr. Lisse think it will not — it could provide a bright and striking addition
to the night sky in early December as it zooms near Earth on its way back out.
The best times for viewing would be right before sunrise or right after sunset.
Currently it is not readily visible because it is too close to the sun.
Video by NASA
In recent years, astronomers have spotted many
sun-grazing comets, but this one is different. Named for the International
Scientific Optical Network in Russia, which discovered it in September 2012, it
appears to have originated in the Oort Cloud, a sphere of debris about a
light-year from the sun. Most of the earlier sun grazers appear to be pieces
from a larger comet that looped around the sun many times.
ISON was probably dislodged a few million years
ago by the gravitational nudge of a passing star, sending it on a trajectory to
the inner solar system for the first time and quite possibly the last.
“And we’re going to watch it bake and boil,” Dr.
Lisse said.
Video by NASA
NASA’s fleet of spacecraft, including the Hubble
Space Telescope and the Mars Reconnaissance Orbiter, have been taking pictures
as the comet entered the inner solar system. “This particular comet is of
extreme interest to us,” said James L. Green, the director of planetary science
at NASA.
Few comets are discovered so far out, and some
scientists at first thought ISON was several miles in diameter and would become
the “Comet of the Century,” rivaling the brightness of a full moon.
But as the comet passed Mars, the NASA orbiter
took pictures showing that it was three-quarters of a mile wide at most, smaller than most comets.
Because ISON was discovered so far away,
astronomers had plenty of time to plan their observations. Measurements by
NASA’s Spitzer Space Telescope, which takes infrared photographs, showed a
large envelope of carbon dioxide around the nucleus. “It is looking like
carbon dioxide may be a very fundamental molecule in that early solar system
rather than carbon monoxide,” Dr. Lisse said.
As ISON approaches the sun, the motions of its
tail reveal the usually invisible movements in the solar wind, the torrent of
particles continually ejected by the sun.
In recent days, the comet has behaved
erratically, brightening and dimming; that has led to speculation that it has
already fallen apart. “We just don’t know if it’s in one piece or not,” said
Karl Battams, an astrophysicist at the Naval Research Laboratory.
Even falling apart could be valuable. Dr. Lisse
said scientists understood how fine dust particles conglomerated into larger
particles the size of BBs and marbles, and they know how comet-size objects can
combine into planets. But they have not figured out how the BB- and marble-size
objects combine into comets.
“When the BBs and the marbles hit each other,
they fall apart,” Dr. Lisse said. By looking at the process in reverse, he went
on, scientists can “see how it got put together” in the first place.
