Starship Asterisk*

[url=http://www.spitzer.caltech.edu/images/5612-ssc2013-06a][b][i]Spitzer Eyes Comet ISON[/i][/b][/url] - [b][i]Credit: NASA/JPL-Caltech/JHU-APL/UCF[/i][/b]

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Astronomers using NASA's Spitzer Space Telescope have observed what most likely are strong carbon dioxide emissions from Comet ISON ahead of its anticipated pass through the inner solar system later this year.

Images captured June 13 with Spitzer's Infrared Array Camera indicate carbon dioxide is slowly and steadily "fizzing" away from the so-called "soda-pop comet," along with dust, in a tail about 186,400 miles long.

"We estimate ISON is emitting about 2.2 million pounds of what is most likely carbon dioxide gas and about 120 million pounds of dust every day," said Carey Lisse, leader of NASA's Comet ISON Observation Campaign and a senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Previous observations made by NASA's Hubble Space Telescope and the Swift Gamma-Ray Burst Mission and Deep Impact spacecraft gave us only upper limits for any gas emission from ISON. Thanks to Spitzer, we now know for sure the comet's distant activity has been powered by gas."

Comet ISON was about 312 million miles from the sun, 3.35 times farther than Earth, when the observations were made.

"These fabulous observations of ISON are unique and set the stage for more observations and discoveries to follow as part of a comprehensive NASA campaign to observe the comet," said James L. Green, NASA's director of planetary science in Washington. "ISON is very exciting. We believe that data collected from this comet can help explain how and when the solar system first formed."

Comet ISON (officially known as C/2012 S1) is less than 3 miles in diameter, about the size of a small mountain, and weighs between 7 billion and 7 trillion pounds. Because the comet is still very far away, its true size and density have not been determined accurately. Like all comets, ISON is a dirty snowball made up of dust and frozen gases such as water, ammonia, methane and carbon dioxide. These are some of the fundamental building blocks which, scientists believe, led to the formation of the planets 4.5 billion years ago.

Comet ISON is believed to be inbound on its first passage from the distant Oort Cloud, a roughly spherical collection of comets and comet-like structures that exists in a space between one-tenth light-year and 1 light-year from the sun. The comet will pass within 724,000 miles of the sun on Nov. 28.

It is warming up gradually as it gets closer to the sun. In the process, different gases are heating up to the point of evaporation, revealing themselves to instruments in space and on the ground. Carbon dioxide is thought to be the gas that powers emission for most comets between the orbits of Saturn and the asteroids.

The comet was discovered Sept. 21, roughly between Jupiter and Saturn, by Vitali Nevski and Artyom Novichonok at the International Scientific Optical Network (ISON) near Kislovodsk, Russia. This counts as an early detection of a comet, and the strong carbon dioxide emissions may have made the detection possible.

"This observation gives us a good picture of part of the composition of ISON, and, by extension, of the proto-planetary disk from which the planets were formed," said Lisse. "Much of the carbon in the comet appears to be locked up in carbon dioxide ice. We will know even more in late July and August, when the comet begins to warm up near the water-ice line outside of the orbit of Mars, and we can detect the most abundant frozen gas, which is water, as it boils away from the comet."

Approaching the sun, Comet ISON floats against a seemingly infinite backdrop of numerous galaxies and a handful of foreground stars. The icy visitor, with its long gossamer tail, appears to be swimming like a tadpole through a deep pond of celestial wonders.

In reality, the comet is much, much closer. The nearest star to the sun is over 60,000 times farther away, and the nearest large galaxy to the Milky Way is over thirty billion times more distant. These vast dimensions are lost in this deep space Hubble exposure that visually combines our view of the universe from the very nearby to the extraordinarily far away.

In this composite image, background stars and galaxies were separately photographed in red and yellow-green light. Because the comet moved between exposures relative to the background objects, its appearance was blurred. The blurred comet photo was replaced with a single, black-and-white exposure. The images were taken with the Wide Field Camera 3 on April 30, 2013.

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

Comet ISON Among the Sparkling Stars

Astronomer Ignacio Ferrin, FACom researcher, has determined the fate of comet C/2012 S1 ISON, described by some as "the comet of the century". The comet has fizzled completely. It is probable that it may disintegrate at or before reaching perihelion.

• arXiv.org > astro-ph > arXiv:1306.5010 > 20 Jun 2013

A press release out yesterday about a recent paper on Comet ISON has caused a mild uproar across the astronomy-minded social media outlets and some websites. (FACom)

The article had professional astronomers and comet enthusiasts alike shaking their heads in disbelief.

For one, any determination of ISON’s ultimate fate when it gets close to the Sun later this year is speculation at best, (as is the case with almost any other sun-grazing comet) and since no one on planet Earth has seen ISON since it entered the Sun’s glare in June, there is absolutely no way to determine the comet’s current state. The almost unanimous shout from the astronomy internets was “we just have to wait and see what happens with ISON.”

But the press release also had this journalist (and others) wondering if Ferrin’s views were taken out of context for the sake of a dramatic press release. ...

... Any hype either way — whether it is calling this the Comet of the Century or a comet that has fizzled — only does a disservice to astronomy, and gives the general public the wrong impression of both the comet and science’s ability to study and predict astronomical phenomenon.

geckzilla wrote:
Ok, stop with the emotional roller coaster.

BDanielMayfield wrote:Ok, well now Comet Ison has come out from behind the sun, but it doesn’t look too good y’all.

... Based on various models, we would estimate that ISON now should be anywhere from about mag 13 to mag 15. Bruce estimates the object in the center of these images to be approximately 14.30 +/- 0.23 –right in the middle of where we would expect ISON to be. ...

Click to play embedded YouTube video.

Around the world, astronomers are buzzing with anticipation over the approach of Comet ISON. On Thanksgiving Day 2013, the icy visitor from the outer solar system will skim the sun's outer atmosphere and, if it survives, could emerge as one of the brightest comets in years.

First, though, it has to fly by Mars.

"Comet ISON is paying a visit to the Red Planet," says astronomer Carey Lisse of the Johns Hopkins University Applied Physics Lab. "On Oct 1st, the comet will pass within 0.07 AU from Mars, about six times closer than it will ever come to Earth."

Mars rovers and satellites will get a close-up view. It’s too early to say whether Curiosity will be able to see the comet from the surface of Mars—that depends on how much ISON brightens between now and then. Lisse says the best bet is NASA’s Mars Reconnaissance Orbiter. The MRO satellite is equipped with a powerful half-meter telescope named HiRISE that is more than capable of detecting the comet’s atmosphere and tail. Observations are planned on four dates: August 20th, Sept 29th, and Oct 1st and 2nd.

HiRISE wasn't sent to Mars to do astronomy, notes the telescope’s principal investigator Alfred McEwen of the University of Arizona. "The camera is designed for rapid imaging of Mars. Our maximum exposure time is limited compared to detectors on other space telescopes. This is a major limitation for imaging comets. Nevertheless, I think we will detect Comet ISON."

The Mars flyby comes at a key time in Comet ISON’s journey. It will have just crossed the "frost line," a place just outside the orbit of Mars where solar heating is enough to start vaporizing frozen water.

"The volatiles in a comet are 80% to 90% water ice," notes Lisse. "Right now in August almost all the water is still frozen, and the outgassing we see in ISON is driven by carbon dioxide and other lesser constituents. Probably only isolated patches of the comet's nucleus are active."

But when ISON crosses the frost line, "the whole comet could erupt in geysers of gas," says Lisse. "Mars orbiters will have a ringside seat."

The amount of outgassing at Mars will give researchers clues to the size of ISON’s nucleus, which is hidden from view deep within the comet’s dusty atmosphere.

"If ISON's nucleus is much bigger than 0.5 km, it will probably survive its Thanksgiving Day brush with the sun," says Lisse. "It could turn into one of the most spectacular comets in many years."

McEwen sees this as a tune-up for another comet encounter next year. "The science value of observing Comet ISON is hard to predict. We've never tried such a thing before. However, this is good practice for Comet Siding Spring, which will pass much closer to Mars in 2014."

For now all eyes are on Comet ISON. An unprecedented number of NASA spacecraft - 16 - will be observing the comet. Astronauts on board the International Space Station will be watching, too.

Meanwhile back on Earth, Lisse is working with NASA to organize a worldwide observing campaign for Comet ISON. "Our goal is to have every telescope on Earth pointed at the comet when it emerges from the sun," says Lisse. "The Mars flyby will give us a sneak preview, providing data we need to predict what we might see."

http://astrobob.areavoices.com/2013/09/25/countdown-to-comet-ison-mars-flyby/ wrote:

[b][color=#0000FF]Beautiful color photo of Comet ISON taken by astrophotographer Damian Peach on Sept. 24. ISON is a dusty comet. Much of that dust is blown back by light pressure from the sun to form the tail. Click to enlarge.[/color][/b]

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Countdown to Comet ISON Mars flyby
Astrobob, September 25, 2013

<<In just 4 days four Mars probes will focus cameras on Comet ISON as it makes its closest approach to the planet on Oct. 1. NASA’s Mars Reconnaissance Orbiter will study and photograph the comet from orbit on three days: Sept. 29, Oct. 1 and Oct. 2. Europe’s Mars Express orbiter, which began its ISON observing campaign on Sept. 21, will study the coma, the tenuous atmosphere that surrounds the comet’s icy nucleus. The probe will examine and photograph ISON through about October 5. As soon as photos are released, you’ll see them here.

Both the Curiosity and Opportunity rovers will also be pressed into service to spy ISON from the ground during the same time. Seen from Mars, the comet should glow about magnitude 2.5-3, plenty bright to see with the naked eye if you could somehow wish yourself there.

Amateur and professional astronomers have been watching Comet ISON evolve since its discovery on Sept. 21, 2012. It began as a dim 15th magnitude patch of haze and brightened very slowly. Amateurs reported a nice uptick in activity beginning late this summer into early fall. ISON now shines at about magnitude 11.5-12 (still faint and requiring a telescope to see) and sports a short tail pointing to the northwest. I was able to see the tail and brighter coma in my 15-inch scope without difficulty about a week ago in a dark sky just before dawn.

Time exposure photos show a classic beauty of a comet with a bright, compact head and elegant tail. According to NASA’s Comet ISON Observing Campaign site, astronomers consider ISON “somewhat more active” that a typical comet. It’s kicking out a lot of dust right now as the sun’s heat vaporizes ice on the comet’s surface. That’s why we see a substantial tail in recent photos. Any guesses as to exactly how bright ISON will become when it zips nearest the sun on Thanksgiving Day are just that … educated guesses.

Astronomers use formulas based on comet size, distance and dust production rate to come up with brightness predictions. ISON could rival Venus for a short time on Nov. 28 or be substantially fainter or brighter. If it survives its searingly close passage of 745,000 miles (1.2 million km) from the sun’s surface, it will likely become a beautiful sight for northern hemisphere skywatchers during the first half of December. Southern hemisphere observers will have their best views before closest approach. Much depends on the the comet’s size, currently estimated at 3 km, pretty typical for a comet. The bigger the iceball, the better the chance of surviving the sun’s battering. Let’s hope ISON keeps it together.>>

As Comet ISON nears the Sun, the big question is whether it will remain intact or shatter into pieces. Since comets are mostly made up of ice, it’s reasonable to suspect that the heat of the Sun causes them to disintegrate. But that’s not the whole story. To discover why comets fall apart, we need to look at the force currently keeping your feet firmly on the ground — gravity. ...

BMAONE23 wrote:http://sohowww.nascom.nasa.gov/data/realtime/mpeg/
Comet ISON coming into the LASCO C3 field of view