Hubble Telescope Catches An Early Glimpse Of "Comet Of The Century".
The reason for those hopes — and the reason for all the "coulds" and "mights" — is that ISON appears to be a long-period comet, coming in from the far reaches of the solar system for the first time in living memory. Such comets are unpredictable: Will they shed lots of dust and glowing gas, or will they turn out to be duds? ISON's orbit is due to bring it within 700,000 miles (1.2 million kilometers) of the sun's surface. That could cause ISON to crumble like Comet Elenin did in 2011, or it could spark a flare-up of Comet Lovejoy proportions. Unlike Comet Lovejoy, which lit up the Southern Hemisphere's skies during 2011's holiday season, Comet ISON should be visible from the Northern Hemisphere — which means Americans might get an eyeful during this year's winter holidays. (There's that pesky "might"!)
The picture from Hubble helps astronomers get a better fix on the current state of Comet ISON: The nucleus appears to be no larger than three or four miles (five to seven kilometers) across. In Tuesday's image release, the Hubble team says that's "remarkably small, considering the high level of activity observed in the comet so far." The comet's fuzzy head, known as the coma, measures about 3,100 miles (5,000 kilometers) across, or a little less than the distance from New York to Dublin. ISON's tail extends more than 57,000 miles, far beyond Hubble's field of view. Detailed readings from Hubble could unlock the secrets of ISON's origins, University of Maryland astronomer Michael A'Hearn said in a news release. "We want to look for the ratio of the three dominant ices, water, frozen carbon monoxide, and frozen carbon dioxide, or dry ice," A'Hearn said. "That can tell us the temperature at which the comet formed, and with that temperature, we can then say where in the solar system it formed." Comet ISON was discovered last September and is formally known as C/2012 S1 (ISON). It takes its name from the International Scientific Optical Network, a group of observatories in 10 countries managed by Russia's Keldysh Institute of Applied Mathematics. - Cosmic Log.
Comet Could Blast Earth With Odd Meteor Shower.A small but incredibly bright comet heading toward the sun could do more than dazzle Earth’s skies when it arrives later this year. Scientists say Comet ISON, already shedding dust at the prodigious rate of about 112,000 pounds per minute, could spark an unusual meteor shower. Computer simulations predicting the location and movement of the comet’s dust trail show Earth will be passing through the fine-grained stream around Jan. 12, 2014. Some of the particles, which are smaller in diameter than a red blood cell, should be pushed back by the pressure of sunlight, allowing them to be captured by Earth’s gravity when the planet plows through the largely invisible stream.
“As the comet passes Earth’s orbit going into the sun, you’ll have particles trailing behind it. But since it’s passing so close to the sun, you’re also going to have particles pushed away by the pressure of the sunlight. That means we’ll have particles coming outward and also falling inward. We don’t often deal with particles that come both directions,” said Bill Cooke, lead scientist at NASA's Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Ala. The particles are so small that even though they will hit the atmosphere at about 125,000 mph, instead of burning up, triggering so-called “shooting stars,” they will be stopped entirely, predicts astronomer Paul Wiegert, with the University of Western Ontario in Canada. The only visible and detectable sign of the comet dust might be a proliferation of bright blue clouds at the edge of space. Scientists suspect these so-called noctilucent, or “night-shining” clouds are be seeded by dust in the upper atmosphere.
Eventually, the trapped comet dust will make its way -- silently and invisibly -- to the planet’s surface. Comet ISON, which was discovered in September 2012 by amateur astronomers in Russia, is believed to be making its first swing into the inner solar system, so unlike repeat fliers, it hasn’t laid down a rich dust trail from previous orbits for Earth to fly through. ISON is an acronym for the telescope the astronomers were using, the International Scientific Optical Network. If the comet survives -- and that’s a big if -- the comet will about 700,000 miles above the surface of the sun when it makes its closest approach on Nov. 28. The closest it will come to Earth will be about 40 million miles on Dec. 26. A comet in the 1970s passed 10 times farther away from the sun than ISON's orbit and partially disintegrated, noted Cooke. “ISON may very well not survive. I guess we won’t know for sure until we look for it to come out from behind the sun,” Cooke told Discovery News. Currently the comet is about 280 million miles away from Earth and approaching the outer part of the asteroid belt. - NBC News.
NASA's ScienceCast - Comet ISON Meteor Shower.Anticipation is building as Comet ISON plunges into the inner solar system for a close encounter with the sun in November 2013. Blasted at point-blank range by solar radiation, the sungrazer will likely become one of the finest comets in many years. When NASA's Swift spacecraft observed the comet in January 2013, it was still near the orbit of Jupiter, but already very active. More than 112,000 pounds of dust were spewing from the comet's nucleus every minute. It turns out, some of that dust might end up on Earth. Veteran meteor researcher Paul Wiegert of the University of Western Ontario has been using a computer to model the trajectory of dust ejected by Comet ISON, and his findings suggest that an unusual meteor shower could be in the offing. "For several days around January 12, 2014, Earth will pass through a stream of fine-grained debris from Comet ISON," says Wiegert. "The resulting shower could have some interesting properties.
WATCH: NASA's ScienceCast - Comet ISON Meteor Shower.
According to Wiegert's computer models, the debris stream is populated with extremely tiny grains of dust, no more than a few microns wide, pushed toward Earth by the gentle radiation pressure of the sun. They will be hitting at a speed of 56 km/s or 125,000 mph. Because the particles are so small, Earth’s upper atmosphere will rapidly slow them to a stop. "Instead of burning up in a flash of light, they will drift gently down to the Earth below," he says. Don’t expect to notice. The invisible rain of comet dust, if it occurs, would be very slow. It can take months or even years for fine dust to settle out of the high atmosphere. While the dust is “up there,” it could produce noctilucent clouds (NLCs).
WATCH: Paul Wiegert's model of the Comet ISON debris stream.
NLCs are icy clouds that glow electric-blue as they float more than 80 km above Earth's poles. Recent data from NASA's AIM spacecraft suggests that NLCs are seeded by space dust. Tiny meteoroids act as nucleating points where water molecules gather; the resulting ice crystals assemble into clouds at the edge of space itself. This is still speculative, but Comet ISON could provide the seeds for a noctilucent display. Electric-blue ripples over Earth's polar regions might be the only visible sign that a shower is underway. Wiegert notes another curiosity: "The shower is going to hit our planet from two directions at once." When Earth passes through the debris stream, we will encounter two populations of comet dust. One swarm of dust will be following the Comet ISON into the sun. Another swarm will be moving in the opposite direction, pushed away from the sun by solar radiation pressure. The streams will pepper opposite sides of Earth simultaneously. "In my experience, this kind of double whammy is unprecedented," says Wiegert. Bill Cooke, lead scientist at NASA's Meteoroid Environment Office, says there's little danger to Earth-orbiting spacecraft. "These particles are just too small to penetrate the walls of our satellites, and they don't stand a chance against the heavy shielding of the ISS." However, he adds, mission operators will be alert around January 12th for possible anomalies. Sky watchers should probably be alert, too. The odds of seeing anything are low, but Comet ISON could prove full of surprises. - NASA.
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