Comet ISON: Forecast for Potential ‘Comet of the Century’ Looks Dim


Comet ISON is not brightening as much as expected as it zooms toward the sun, an amateur astronomer has reported, dealing a blow to skywatchers hoping for a spectacular show from the icy wanderer during its close solar approach this November.

ISON, which almost immediately after its discovery last September was branded as a “comet of the century” candidate, now seems in jeopardy of completely disintegrating before skimming just 724,000 miles (1.16 million kilometers) above the surface of the sun on Thanksgiving Day (Nov. 28).

Since early June, ISON has been unobservable because of its close proximity to the sun in our sky. The comet is now slowly moving out of the bright solar glare and is becoming better placed for viewing in the morning, low in the eastern sky just before sunrise. [Photos of Comet ISON: A Potentially Great Comet]


When the comet vanished a couple of months ago, it had brightened very little if at all since the beginning of 2013. Astronomers had hoped that, while masked by the light of the sun, ISON would begin brightening at a more robust pace as it drew nearer to our star.

Unfortunately, that has not happened.

Early on Monday (Aug. 12), Arizona amateur astronomer Bruce Gary became the first person to pick up Comet ISON since it disappeared in early June. By stacking images acquired by an 11-inch telescope pointing just 6 degrees above the eastern dawn horizon, he succeeded in recording a fuzzy patch of light with a short tail at the comet’s predicted position among stars that are as faint as magnitude 16.

Measuring the image, Gary — a retired radio astronomer and atmospheric scientist — came up with a total magnitude of 14.3 ± 0.2. That is at least two magnitudes fainter than most predictions, and more than a thousand times fainter than the dimmest star that can be perceived with the unaided eye.

Gary’s observation does not bode well for ISON’s future performance, experts say.

“That the comet continues to appear as faint as it does implies that its intrinsic brightness (absolute magnitude) is low and that the nucleus is probably small and relatively inactive,” said well-known comet observer John Bortle.

Bortle added that, in his opinion, “ISON has no chance of surviving its perihelion, based on my paper ‘Post-Perihelion Survival of Comets with Small q’ (International Comet Quarterly, Vol. 13, No. 3, July 1991).”

Of course, such forecasts are based on just one set of photographs. During the coming weeks, many other observations of ISON made by amateur and professional astronomers worldwide, as well as by orbiting satellites, will give us a much better assessment of ISON’s chances.

In light of this, Bortle stresses that he is hedging his bets: “I wouldn’t fully commit to such until I see some actual visual observations reported.”

We here at will have another update on ISON when more of those observations become available at the end of this month, so stay tuned!

Mighty Comet ISON: Space and Earth Telescopes to Track ‘Comet of the Century’

by Clara Moskowitz, Assistant Managing Editor   |   August 06, 2013 05:30pm ET
The Hubble Space Telescope captured this view of Comet ISON, C/2012 S1 (ISON), on May 8, 2013.
The Hubble Space Telescope captured this view of Comet ISON, C/2012 S1 (ISON), on May 8, 2013 as it streaked between the orbits of Jupiter and Mars at a speed of about 48,000 mph.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

LAUREL, Md. — All eyes on the sky that can do so will be pointing toward Comet ISON soon, as a massive international observing campaign gets underway to watch what could become the “comet of the century,” scientists say.

Comet ISON was discovered in September 2012, and is due to swoop in close to the sun in November. When it does, it may become as bright as the full moon, visible to the naked eye even in daylight. Or, it may not.

What will happen to Comet ISON is an open question to scientists, who hope to learn more about what causes certain comets to flare brightlyand others to fizzle out and evaporate under the sun’s radiation. [Photos of Comet ISON: A Potentially Great Comet]



Uncertain fate

“We don’t have anything to directly compare to ISON,” astronomer Matthew Knight of the Lowell Observatory in Flagstaff, Ariz., said Thursday (Aug. 1) here at the Johns Hopkins University Applied Physics Laboratory during a two-day workshop on observing ISON. Based on historical records, he said, very large comets tend to survive their encounters with the sun, while smaller ones evaporate or break into pieces under the harsh solar radiation. Comet ISON is a mid-sized comet, and its fate is very uncertain.

ISON is thought to originate in the Oort cloud, a large spherical cloud of small planetary fragments that is thought to surround the sun and extend up to a light-year out. The comet was first discovered in September of 2012, and belongs to a class of bodies called sungrazing comets that skim in close to the sun’s atmosphere.

Under the banner of a coordinated observing program called the NASA Comet ISON Observing Campaign, dozens of observatories on the ground, in space, and even on sounding rockets and high-altitude balloons, will watch the comet’s progress toward the sun this fall.

Starting at Mars

One of the first major series of observations will be taken from orbit around Mars, which will have a view of ISON as it moves toward the inner solar system. NASA’s Mars Reconnaissance Orbiter (MRO), plans to snap photos of ISON on Aug. 20, when the comet makes its closest approach to the Red Planet.

“The Aug. 20 observations might give you all an early indication of just how bright the comet has become, at least at this time and place,” said Richard Zurek, chief scientist of the Mars Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. [Comet ISON: Evolution of a Potentially Great Comet (A Timeline)]

In addition to MRO, NASA’s Mars rovers Curiosity and Opportunity will try to take photos of Comet ISON as it appears in the Martian sky overhead.

After ISON zooms by Mars, it will soon approach Mercury, the innermost planet in the solar system. There, NASA’s Messenger probe orbiting the tiny planet will make observations of the comet.

And finally, as it nears the sun, three solar observatories will switch into high gear mode to watch ISON rendezvous with our star, where it will make its closest approach on Nov. 28. NASA’s SOHO (Solar & Heliospheric Observatory), STEREO (Solar TErrestrial RElations Observatory) and SDO (Solar Dynamics Observatory) spacecraft will all turn their sights on the possible “comet of the century.”

Observing throughout the spectrum

Comet ISON Photos by Spitzer Space Telescope
These images from NASA’s Spitzer Space Telescope of Comet ISON were taken on June 13, 2013, when ISON was 312 million miles (502 million kilometers) from the sun. The lefthand image shows a tail of fine rocky dust issuing from the comet, blown back by the pressure of sunlight. The image at right shows a neutral gas atmosphere surrounding ISON, likely created by carbon dioxide fizzing off the comet at a rate of 2.2 million pounds per day.

Space telescopes that specialize in observing through certain wavelengths of light will each have their special roles to play in the campaign. NASA’s Swift satellite will photograph ISON in gamma-ray light, while the Spitzer Space Telescope will observe in infrared light and the Chandra Observatory will look in X-rays.

Not to be outdone, dozens of telescopes on the ground will also contribute to observations of Comet ISON, including the Lowell Observatory, the Arecibo radio dish in Puerto Rico, and the Submillimeter Array in Hawaii, just to name a few.

This coordinated effort will help scientists catch ISON in action, as its transformation during its close encounter with the sun could be rapid.

“ISON isn’t up for very long in any one area — not enough to characterize it,” Knight said. “We’d like to combine observations from around the world — as many longitudes as we can get — and collect them all. You get roughly 24-hour coverage. From that we may be able to piece together what’s going on.”

Dedicated missions

While many observatories will be diverting from normal work to observe ISON, some missions have been designed for this comet specifically.

One project is a small sounding rocket mission dubbed FORTIS (Far-ultraviolet Off Rowland-Circle for Imaging and Spectroscopy) that will measure ultraviolet light from Comet ISON during a short 5-6 minute observing window while the rocket flies up to the edge of space and back.

Another mission dedicated to ISON is the BRRISON (Balloon Rapid Response for ISON) mission, which will loft a telescope on a high-altitude balloon designed to travel 120,000 feet (37,000 meters) up to Earth’s stratosphere, where it can observe in infrared and near ultraviolet/visible wavelengths.

“I don’t need to tell this audience why ISON is such an unusual opportunity,” said BRRISON’s principal investigator, Andrew Cheng of the Applied Physics Laboratory. “It’s a sungrazer, unusually bright, it’s also an Oort cloud comet, probably on its first visit to the inner solar system, preserving icy material that was formed in the very early days of our solar system.”

Comet ISON Could Put On a Great Light Show

per webpronews:


By  · 18 hours ago


In November of 2013, the universe is throwing a “dirty snowball” right within sight of our Earth. And it could end up being a spectacular sight.

Comet ISON, named after the International Scientific Optical Network, a Russian program that discovered the comet last year. This particular comet is anywhere from 1 to 10 kilometers in size, based on what can be seen of it at this point. It just looks like a tiny speck right now.

But ISON is a “sun-grazer”. It will fly through the sun’s atmosphere little more than a million km from the stellar surface. And as it nears the sun, it will start shedding ice and particles from its surface, really becoming visible. But a comet that gets this close to the sun could even fly completely apart, the result of which would be a magnificent light show. Even if it survives this trip past the sun, 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.

Or the whole thing could fizzle. 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.”

The trouble with comets is that they are basically “dirty snowballs” flying toward the sun. Tidal forces and solar radiation have been known to destroy comets. A recent example is Comet Elenin, which broke apart and dissipated in 2011 as it approached the sun.

However, another comet that we could compare ISON to 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 probably at least twice as big as Comet Lovejoy and will pass a bit farther from the sun’s surface,” notes Matthew Knight of the Lowell Observatory. “This would seem to favor Comet ISON surviving and ultimately putting on a good show.”

If ISON does make it through it’s whip around the sun on Thanksgiving Day, it could be visible all night in parts of December and January.

Even if ISON breaks up, there is no danger to Earth. The pieces would continue right along the same path the original comet was on.