Starship Asterisk*

Peter Grego, Astronomy Now wrote:
A new comet has been discovered that is predicted to blaze incredibly brilliantly in the skies during late 2013. With a perihelion passage of less than two million kilometres from the Sun on 28 November 2013, current predictions are of an object that will dazzle the eye at up to magnitude —16. That's far brighter than the full Moon.

If predictions hold true then C/2012 S1 will certainly be one of the greatest comets in human history, far outshining the memorable Comet Hale-Bopp of 1997 and very likely to outdo the long-awaited Comet Pan-STARRS (C/2011 L4) which is set to stun in March 2013.

[i]The comet will be 'chasing' the sun as both move east. After perihelion, the comet will swing hard to the north. While the comet's predicted path is very precisely known; tail lengths are only guesses. (Courtesy: unmannedspaceflight.com member Gladstoner)[/i]

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2013 is looking to be a promising year for potential naked-eye comets, as a new comet has been discovered that will likely skirt close to the Sun, and could provide a stunning display late next year. The comet, named Comet C/2012 S1 (ISON), as it was discovered by a Russian team at the International Scientific Optical Network (ISON), is currently about the distance of Jupiter’s orbit. But it is projected to come within less than 2 million km from the Sun at perihelion by November 28, 2013. Ernesto Guido and Giovanni Sostero from the Remanzacco Observatory in Italy, along with their colleague Nick Howes from the UK have imaged the comet with the RAS telescope in New Mexico, and say, “According to its orbit, this comet might become a naked-eye object in the period November 2013 – January 2014. And it might reach a negative magnitude at the end of November 2013.”

This new comet joins Comet C/2011 L4 PanSTARRS, which is projected to come within 45 million kilometers (28 million miles) of the Sun on March 9, 2013, which is close enough for quite a bit of cometary ice to vaporize and form a bright coma and tail. Comet PanSTARRS will be visible at perihelion to southern hemisphere, while Comet ISON should be visible to mid-latitude northern hemisphere skywatchers, according to the Remanzacco team. ...

It looks potentially very interesting indeed. The orbit is very well-determined. We can say, with complete confidence, that it'll come very close to the sun (about 0.012 AU, almost but not quite "sun-grazing") on 29 November 2013, plus or minus a day. At that point, it might get very bright, as some sungrazing comets have in the past (such as Ikeya-Seki in 1965, and C/2006 P1 McNaught in 2007).

So we're quite sure where it's going. The uncertain part (as always with comets) is how bright it'll be.

I expect that it'll at least be of considerable interest to comet observers, much as C/2006 P1 was. But estimating comet brightnesses a year ahead of time is about like asking who's going to win the World Series next year. It could be astonishingly bright, or it could fizzle. I think it was David Levy who said that comets are like cats: they have tails, and do whatever they want to do. ...

http://tech.groups.yahoo.com/group/come ... sage/19829

Unless you’ve been cut off from the internet today you’ll have heard about The Comet. No, not Comet PANSTARRS, which is due to shine in the sky next March, perhaps rivalling the fondly-remembered Comet Hale Bopp from 1996, but another comet. Comet 2012/S1, or “Comet ISON” to give it its full name. It’s everywhere you look on Twitter, Facebook, Google Plus. Why? Because initial calculations of its orbit show it will pass ridiculously close to the Sun next November, skimming the solar surface at a height of just under two million kilometres. And that means it might shine jaw-droppingly bright in the sky at that time, before it heads back off into deep space again.

So, of course, adding two and two to get fifty, there are lots of people getting more excited about this comet than a dog in a lamp post factory. If you were to believe some of the comments being written about it, it is absolutely nailed-on guaranteed to shine like a welding torch in the sky next November, blazing at magnitude -16, with a tail stretching across the sky like a WW2 searchbeam.

Can we all just calm down, please? ...

Beyond wrote:Huh, i didn't know about either one, or i forgot. But i think i didn't know. So I'm not excited. Unless one or both start lighting up the night.

bystander wrote:

Beyond wrote:Huh, i didn't know about either one, or i forgot. But i think i didn't know. So I'm not excited. Unless one or both start lighting up the night.

We won't get to see PanSTARRS. It's another Southern hemisphere comet. ISON, however, may be visible in the North.

Orca wrote:There is the possibility of a comet visible to the naked eye in the northern hemisphere next year:

http://news.discovery.com/space/new-com ... 20925.html

In a nutshell: we can predict its path but not what will actually happen when it gets "good and close." The possibilities range from 'spectacular event' to 'minor fizzle.'

Click to play embedded YouTube video.

NASA's Deep Impact spacecraft has acquired its first images of comet C/2012 S1 (ISON). The images were taken by the spacecraft's Medium-Resolution Imager over a 36-hour period on Jan. 17 and 18, 2013, from a distance of 493 million miles (793 million kilometers). Many scientists anticipate a bright future for comet ISON; the spaceborne conglomeration of dust and ice may put on quite a show as it passes through the inner solar system this fall.

"This is the fourth comet on which we have performed science observations and the farthest point from Earth from which we've tried to transmit data on a comet," said Tim Larson, project manager for the Deep Impact spacecraft at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The distance limits our bandwidth, so it's a little like communicating through a modem after being used to DSL. But we're going to coordinate our science collection and playback so we maximize our return on this potentially spectacular comet."

Deep Impact has executed close flybys of two comets - Tempel 1 and Hartley 2 - and its mission scientists, led by University of Maryland Astronomer Michael A'Hearn, have performed scientific observations on two more - comet Garradd and now ISON. The ISON imaging campaign is expected to yield infrared data, and light curves (which are used in defining the comet's rotation rate) in addition to visible-light images. A movie of comet ISON was generated from initial data acquired during this campaign. Preliminary results indicate that although the comet is still in the outer solar system, more than 474 million miles (763 million kilometers) from the sun, it is already active. As of Jan. 18, the tail extending from ISON's nucleus was already more than 40,000 miles (64,400 kilometers) long.

Long-period comets like ISON are thought to arrive from the solar system's Oort cloud, a giant spherical cloud of icy bodies surrounding our solar system so far away its outer edge is about a third of the way to the nearest star (other than our sun). Every once in a while, one of these loose conglomerations of ice, rock, dust and organic compounds is disturbed out of its established orbit in the Oort cloud by a passing star or the combined gravitational effects of the stars in the Milky Way galaxy. With these gravitational nudges, so begins a comet's eons-long, arching plunge toward the inner solar system.

ISON was discovered on Sept. 21, 2012, by two Russian astronomers using the International Scientific Optical Network's 16-inch (40-centimeter) telescope near Kislovodsk. NASA's Near-Earth Object Program Office, based at JPL, has plotted its orbit and determined that the comet is more than likely making it first-ever sweep through the inner solar system. Having not come this way before means the comet's pristine surface has a higher probability of being laden with volatile material just spoiling for some of the sun's energy to heat it up and help it escape. With the exodus of these clean ices could come a boatload of dust, held in check since the beginnings of our solar system. This released gas and dust is what is seen on Earth as comprising a comet's atmosphere (coma) and tail.

ISON will not be a threat to Earth - getting no closer to Earth than about 40 million miles on Dec. 26, 2013. But stargazers will have an opportunity to view the comet's head and tail before and after its closest approach to the sun -- if the comet doesn't fade early or break up before reaching the sun.

Launched in January 2005, NASA's Deep Impact spacecraft traveled about 268 million miles (431 million kilometers) to the vicinity of comet Tempel 1. On July 3, 2005, the spacecraft deployed an impactor that was essentially "run over" by the nucleus of Tempel 1 on July 4. Sixteen days after comet encounter, the Deep Impact team placed the spacecraft on a trajectory to fly past Earth in late December 2007. This extended mission of the Deep Impact spacecraft culminated in the successful flyby of comet Hartley 2 on Nov. 4, 2010. In January of 2012, the spacecraft performed, from a distance, an imaging campaign on comet C/2009 P1 (Garradd).

To date, Deep Impact has traveled about 4.39 billion miles (7.06 billion kilometers) in space.

The Ultraviolet/Optical Telescope aboard NASA's Swift imaged comet ISON (center)
on Jan. 30, when it was located about 3.3 degrees from the bright star Castor
in the constellation Gemini. At the time of this 5.5-minute optical exposure,
ISON was about 5,000 times fainter than the limit of human vision.
(Credit: NASA/Swift/D. Bodewits, UMCP)

From now through October, comet ISON tracks through the
constellations Gemini, Cancer and Leo as it falls toward the sun.
(Credit: NASA/GSFC/Axel Mellinger, Central Michigan Univ)

Click to play embedded YouTube video.

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Astronomers from the University of Maryland at College Park (UMCP) and Lowell Observatory have used NASA's Swift satellite to check out comet C/2012 S1 (ISON), which may become one of the most dazzling in decades when it rounds the sun later this year.

Using images acquired over the last two months from Swift's Ultraviolet/Optical Telescope (UVOT), the team has made initial estimates of the comet's water and dust production and used them to infer the size of its icy nucleus.

"Comet ISON has the potential to be among the brightest comets of the last 50 years, which gives us a rare opportunity to observe its changes in great detail and over an extended period," said Lead Investigator Dennis Bodewits, an astronomer at UMCP.

Additional factors, including an encounter with Mars followed by a scorching close approach to the sun, make comet ISON an object of special interest. In late February, at NASA's request, a team of comet experts initiated the Comet ISON Observing Campaign (CIOC) to assist ground- and space-based facilities in obtaining the most scientifically useful data.

Like all comets, ISON is a clump of frozen gases mixed with dust. Often described as "dirty snowballs," comets emit gas and dust whenever they venture near enough to the sun that the icy material transforms from a solid to gas, a process called sublimation. Jets powered by sublimating ice also release dust, which reflects sunlight and brightens the comet.

Typically, a comet's water content remains frozen until it comes within about three times Earth's distance to the sun. While Swift's UVOT cannot detect water directly, the molecule quickly breaks into hydrogen atoms and hydroxyl (OH) molecules when exposed to ultraviolet sunlight. The UVOT detects light emitted by hydroxyl and other important molecular fragments as well as sunlight reflected from dust.

The Jan. 30 UVOT observations reveal that ISON was shedding about 112,000 pounds (51,000 kg) of dust, or about two-thirds the mass of an unfueled space shuttle, every minute. By contrast, the comet was producing only about 130 pounds (60 kg) of water every minute, or about four times the amount flowing out of a residential sprinkler system.

"The mismatch we detect between the amount of dust and water produced tells us that ISON's water sublimation is not yet powering its jets because the comet is still too far from the sun," Bodewits said. "Other more volatile materials, such as carbon dioxide or carbon monoxide ice, evaporate at greater distances and are now fueling ISON's activity."

At the time, the comet was 375 million miles (604 million km) from Earth and 460 million miles (740 million km) from the sun. ISON was at magnitude 15.7 on the astronomical brightness scale, or about 5,000 times fainter that the threshold of human vision.

Similar levels of activity were observed in February, and the team plans additional UVOT observations.

While the water and dust production rates are relatively uncertain because of the comet's faintness, they can be used to estimate the size of ISON's icy body. Comparing the amount of gas needed for a normal comet to blow off dust at the rate observed for ISON, the scientists estimate that the nucleus is roughly 3 miles (5 km) across, a typical size for a comet. This assumes that only the fraction of the surface most directly exposed to the sun, about 10 percent of the total, is actively producing jets.

An important question is whether ISON will continue to brighten at the same pace once water evaporation becomes the dominant source for its jets. Will the comet sizzle or fizzle?

"It looks promising, but that's all we can say for sure now," said Matthew Knight, an astronomer at Lowell Observatory in Flagstaff, Ariz., and a member of the Swift and CIOC teams. "Past comets have failed to live up to expectations once they reached the inner solar system, and only observations over the next few months will improve our knowledge of how ISON will perform."

Based on ISON's orbit, astronomers think the comet is making its first-ever trip through the inner solar system. Before beginning its long fall toward the sun, the comet resided in the Oort comet cloud, a vast shell of perhaps a trillion icy bodies that extends from the outer reaches of the planetary system to about a third of the distance to the star nearest the sun.

Formally designated C/2012 S1 (ISON), the comet was discovered on Sept. 21, 2012, by Russian astronomers Vitali Nevski and Artyom Novichonok using a telescope of the International Scientific Optical Network located near Kislovodsk.

The first of several intriguing observing opportunities occurs on Oct. 1, when the inbound comet passes about 6.7 million miles (10.8 million km) from Mars.

"During this close encounter, comet ISON may be observable to NASA and ESA spacecraft now working at Mars," said Michael Kelley, an astronomer at UMCP and also a Swift and CIOC team member. "Personally, I'm hoping we'll see a dramatic postcard image taken by NASA's latest Mars explorer, the Curiosity rover."

Fifty-eight days later, on Nov. 28, ISON will make a sweltering passage around the sun. The comet will approach within about 730,000 miles (1.2 million km) of its visible surface, which classifies ISON as a sungrazing comet. In late November, its icy material will furiously sublimate and release torrents of dust as the surface erodes under the sun's fierce heat, all as sun-monitoring satellites look on. Around this time, the comet may become bright enough to glimpse just by holding up a hand to block the sun's glare.

Sungrazing comets often shed large fragments or even completely disrupt following close encounters with the sun, but for ISON neither fate is a forgone conclusion.

"We estimate that as much as 10 percent of the comet's diameter may erode away, but this probably won't devastate it," explained Knight. Nearly all of the energy reaching the comet acts to sublimate its ice, an evaporative process that cools the comet's surface and keeps it from reaching extreme temperatures despite its proximity to the sun.

Following ISON's solar encounter, the comet will depart the sun and move toward Earth, appearing in evening twilight through December. It will swing past Earth on Dec. 26, approaching within 39.9 million miles (64.2 million km) or about 167 times farther than the moon.

Whether we'll look back on ISON as a "comet of the century" or as an overhyped cosmic dud remains to be seen, but astronomers are planning to learn the most they can about this unusual visitor no matter what happens.

Click to play embedded YouTube video.

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.

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).

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.

Click to view full size image 1 or image 2

This NASA Hubble Space Telescope image of Comet C/2012 S1 (ISON) was photographed on April 10, when the comet was slightly closer than Jupiter's orbit at a distance of 386 million miles from the Sun (394 million miles from Earth).

Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. A detailed analysis of the dust coma surrounding the solid, icy nucleus reveals a strong jet blasting dust particles off the sunward-facing side of the comet's nucleus.

Preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than three or four miles across. This is remarkably small considering the high level of activity observed in the comet so far, said researchers. Astronomers are using these images to measure the activity level of this comet and constrain the size of the nucleus, in order to predict the comet's activity when it skims 700,000 miles above the Sun's roiling surface on November 28.

The comet's dusty coma, or head of the comet, is approximately 3,100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles, far beyond Hubble's field of view.

More careful analysis is currently underway to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.

This image was taken in visible light with Hubble's Wide Field Camera 3. The blue false color was added to bring out details in the comet's structure.

A contrast-enhanced image produced from the Hubble images of Comet C/2012 S1 (ISON) is used to reveal the subtle structure in the inner coma of the comet (mouse-over). In this computer-processed view, the Hubble image has been divided by a computer model coma that decreases in brightness proportionally to the distance from the nucleus, as expected for a comet that is producing dust uniformly over its surface. ISON's coma shows enhanced dust particle release on the sunward-facing side of the comet's nucleus, the small, solid body at the core of the comet. This information is invaluable for determining the comet's shape, evolution, and spin of the solid nucleus.

Credit: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team

Hubble Captures Comet ISON
Comet ISON is potentially the "comet of the century" because around the time the comet makes its closest approach to the Sun, on November 28, it may briefly become brighter than the full Moon.

Comets always seem to bring ‘em out of the wood work.

There’s a scene from the 1998 movie Deep Impact where the president, played by Morgan Freeman, reveals a terrible truth… the U.S. government has known for over a year that a doomsday comet is headed straight towards Earth, with Hollywood CGI destruction sure to follow.

While dramatic, the scenario is also extremely implausible. On any given evening, amateur astronomers are sweeping the skies using telescopes mounted in backyard observatories that are the envy of many major universities. This effort to discover comets is collaborative and worldwide. If the “Big One” were headed our way, even the likes of Morgan Freeman couldn’t keep it secret.

Trouble is, many unfounded claims are already making their way around the internet about this years’ much anticipated “Comet of the Century,” C/2012 S1 ISON.

Many of these conspiracy theories seem to be a recycling of last years’ Nibiru nonsense. The train of thought runs something like this: Does NASA know something that they’re not telling us? Why are they so interested in this comet? We’ve even had folks ask us why certain patches of Google Earth are “blacked out!”

What ARE they hiding, man?

It’s funny how pseudoscience seems to bubble to the top on YouTube, but I won’t give these conspiracy videos the exposure of the Universe Today platform. With hundreds of thousands of hits, they certainly don’t seem to need it. A simple YouTube search of “ISON” will scare up many wacky ideas about the comet.

In any event, we’ve already fielded several questions from friends and the public on the “dangers” posed by this comet, so we can only imagine that these will grow in intensity as the comet approaches the inner solar system, especially if it performs up to expectations. ...

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Click to play embedded YouTube video.

This July 4th the solar system is showing off some fireworks of its own.

Superficially resembling a skyrocket, Comet ISON is hurtling toward the Sun at a whopping 48,000 miles per hour.

Its swift motion is captured in this time-lapse movie made from a sequence of pictures taken May 8, 2013, by NASA's Hubble Space Telescope. At the time the images were taken, the comet was 403 million miles from Earth, between the orbits of Mars and Jupiter.

The movie shows a sequence of Hubble observations taken over a 43-minute span, compressed this into just five seconds. The comet travels 34,000 miles in this brief video, or 7 percent of the distance between Earth and the Moon. The deep-space visitor streaks silently against the background stars.

Unlike a firework, the comet is not combusting, but in fact is pretty cold. Its skyrocket-looking tail is really a streamer of gas and dust bleeding off the icy nucleus, which is surrounded by a bright, star-like-looking coma. The pressure of the solar wind sweeps the material into a tail, like a breeze blowing a windsock.

As the comet warms as it moves closer to the Sun, its rate of sublimation will increase. The comet will get brighter and the tail grows longer. The comet is predicted to reach naked-eye visibility in November.

The comet is named after the organization that discovered it, the Russia-based International Scientific Optical Network.

This false-color, visible-light image was taken with Hubble's Wide Field Camera 3.

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)