Comet ISON, a much-anticipated first-time visitor to the inner solar system, will likely survive its Thanksgiving Day encounter with the sun and become visible without binoculars or telescopes to observers on Earth in December, scientists said Wednesday.
Since its discovery in September 2012, Comet ISON has been a bit of a puzzle. At first, the comet was considered unusually bright because it was spotted by astronomers far beyond Jupiter's orbit, raising the prospect that it might be visible on Earth even in daylight.
However, later observations showed the comet was not brightening as much as predicted as it moved closer to the sun. Heating from the sun vaporizes ices in the comet's body, creating a long, glowing tail.
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Another issue was whether Comet ISON would survive its relatively close brush with the sun. On Nov. 28 -- Thanksgiving Day, as it turns out -- the comet will pass about 1 million kilometers, or about 621,000 miles, from the sun's surface. As it blasts around the sun, traveling 234 miles per second, the comet will be heated to about 5,000 degrees Fahrenheit, hot enough to vaporize rock and metals.
The comet also will have to deal with the sun's gravity, which could be strong enough to break apart the comet's body, even if it survived the heating.
But new analysis shows Comet ISON's survival chances are improving.
"We do predict that Comet ISON is likely to survive perihelion," said astronomer Matthew Knight, with the Lowell Observatory, referring to the technical term describing the point in the orbit of a comet, asteroid or planet that is closest to the sun.
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Knight and colleagues studied whether Comet ISON is large enough to survive perihelion despite losing vast amounts of material to solar heating. The team also assessed the comet's ability to withstand the sun's gravitational tugs.
The analysis showed Comet ISON should emerge from its pass around the sun with both its nucleus and tail intact -- unlike what happened to another sun-grazer, Comet Lovejoy, which lost its body during its December 2011 solar rendezvous.
"Having a nucleus after perihelion is good thing," Knight said.
If predictions prove correct, the comet should be visible to the naked eye in Earth's early morning skies in early December and throughout the night beginning in January.
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Comet-observing campaigns, however, may not be as robust as planned, as the ongoing partial furlough of U.S. government employees next week will spread to the National Optical Astronomy Observatory and other telescopes. Already, missions aboard NASA's air-borne SOFIA observatory have been grounded and the National Radio Astronomy Observatory is shut down.
"To my knowledge, (the shutdown) hasn't had a huge impact, but there is potential going forward that it certainly will," Knight told Discovery News.
Based on its flight path, scientists believe Comet ISON is traveling into the inner solar system from the Oort Cloud, a reservoir of icy bodies located beyond Neptune's orbit, for the first -- and probably last -- time.
If it survives, calculations show Comet ISON will be bumped out of the solar system after its swing around the sun.
The comet is named for the International Scientific Optical Network, or ISON, located near Kislovodsk, Russia, which made the first observation of the comet.
The research was presented at a webcast press conference during the American Astronomical Society meeting in Denver this week.