Saturday, December 29, 2012

More on the ISON Comet

I've previously posted about the ISON comet (here and here). However, I noticed several news stories about it during the past week, so I thought I would see if there was any additional information. So far, not much. The orbital information seems to be still the same; as is the uncertainty on whether it will be spectacular or a dud. 

Discovery News has a couple articles. The first, here, reports:
The International Astronomical Union's Minor Planet Center predicts Comet ISON could be visible without binoculars or telescopes to skywatchers on Earth from early November through the first few weeks of January 2014.
NASA's Mars Curiosity rover also may get a look when the comet sails past the red planet in early October.
The comet's journey likely started in the Oort Cloud, a cluster of icy rocks that circle the sun about 50,000 times farther away than Earth's orbit. Comet ISON is expected to pass as close as 700,000 miles, or 1.1 million kilometers, from the sun on Nov. 28.
If it survives, the comet could be the brightest to appear in Earth's skies since 1965 and could even be visible in daylight.
The other article, here, notes:
So why all the uncertainty over Comet ISON's brightness as it careens through the inner solar system?

Comets originate from the outermost reaches of the solar system and are composed of icy volatiles such as water, carbon monoxide, carbon dioxide, methane and ammonia, plus dust, rocks and any other debris that happened to be floating around as our sun evolved. In the case of Comet ISON, it appears to originate from a hypothetical cloud of frozen comets surrounding the solar system.

The Oort Cloud -- located approximately one light-year from the sun -- is thought to contain billions of cometary nuclei that formed during the early evolution of the solar system.

"This is quite possibly a 'new' comet coming in from the Oort cloud, meaning this could be its first-ever encounter with the sun," added Battams. "If so, with all those icy volatiles intact and never having been truly stressed (thermally and gravitationally), the comet could well disrupt and dissipate weeks or months before reaching the sun."
As comets approach the sun, the increase in solar energy causes frozen volatiles to sublime -- i.e., turn from a solid ice to vapor, without passing through a liquid phase. This sublimation causes an eruption of gas and dust that gets swept back by the solar wind, forming a tail. The solid cometary nucleus continues its journey past the sun and, depending on its constituents, can create a very impressive tail that scatters sunlight, producing an impressively bright show.

But it all depends on what material the comet contains and how it formed in deep space. The comet may erupt early, fracture and break apart long before close approach, or it may remain solid long after it has swung past the sun, releasing very little material.

... According to the ace comet-hunters at Remanzacco Observatory, Italy, ISON will make closest approach with Earth around the beginning of January 2014 -- at a distance of 0.4 AU (that's 40 percent the Earth-sun distance, or 60 million kilometers).

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