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TOPIC: Comet 17P/Holmes


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RE: Comet 17P/Holmes
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Comet 17P/Holmes coma now over 5.5 million km wide: 4 times size of the sun!
Using my photograph of the 29th, astrometrically measured with Astrorecord, I updated my diagram of the growing size of comet 17P/Holmes' coma.

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Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   m1    
2008 01 05 02 59.41 +43 28.0 2.030 2.734 126.7 16.8 18.1
2008 01 10 03 01.13 +42 43.8 2.097 2.755 122.7 17.5 18.2
2008 01 15 03 03.59 +42 02.5 2.168 2.777 118.6 18.1 18.3
2008 01 20 03 06.71 +41 24.3 2.242 2.798 114.6 18.6 18.5
2008 01 25 03 10.44 +40 49.2 2.319 2.820 110.6 19.1 18.6
2008 01 30 03 14.71 +40 17.3 2.399 2.842 106.6 19.4 18.7


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Title: A novel mechanism for outbursts of Comet 17P/Holmes and other short-period comets
Authors: Richard Miles

A mechanism is proposed to explain the outburst of comet 17P/Holmes based on; (a) oxidation of water within the porous surface of the comet nucleus to form hydrogen peroxide (H2O2) through exposure to UV radiation, to energetic solar-wind particles and to cosmic radiation, (b) concentration of the H2O2 component through solid-, liquid- and gas-phase processes involving sublimation, evaporation, fractional crystallization, diffusion, supercooling, capillary wetting and migration in voids within the nucleus, and (c) rapid exothermic decomposition of aqueous H2O2 liberating oxygen gas via a surface catalytic reaction through interaction with finely-dispersed transition metals, metal compounds and minerals, in particular those containing Fe, localised within a differentiated multi-component comet nucleus. An accelerated release of gaseous oxygen, concomitant self-heating and volatilisation of hydrocarbons within the nucleus results in its explosive disruption. This mechanism may also explain the observation of a repeat outburst of this comet in 1893. Laboratory studies to investigate H2O2 formation in simulated cometary environments and to evaluate H2O2 decomposition on meteoritic samples are recommended.

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In early November, Don Primi found a new star as he sat on his dock at
1 a.m.
As he observed the object's fuzzy image, the deeply religious amateur astronomer hoped he'd discovered an unknown comet.
Primi soon learned, however, the object that he and other astronomers had noticed was Comet 17P/Holmes, documented first in 1892.

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Comet 17P/Holmes, which dazzled sky watchers with a dramatic outburst that made it visible to the unaided eye, now is fading from sight. However, before it returns to the obscurity from which it came, astronomers at the MMT Observatory took a final look.
In late October, Holmes brightened by a factor of about one million times when it ejected a vast cloud of dust and gas. That cloud expanded over time and now spans more than 870,000 miles, making it larger than the Sun (which is 865,000 miles in diameter).

17P
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Credit M. Ashby & N. Caldwell (CfA)

On November 4, Smithsonian scientists snapped this photo of Comet Holmes using an instrument called Megacam, which is one of the largest CCD cameras in existence. Megacam holds 36 9-megapixel CCD chips, for a total of more than 300 megapixels.
Separate exposures through three colour filters were combined to make this final, full-colour image. Individual stars appear as a line of coloured dots because the photos were centred on the comet, which moved slightly across the sky.
Currently, Comet Holmes has a total brightness of 3rd magnitude, however its large size on the sky (and resulting low surface brightness) makes it difficult to see without binoculars or a telescope. However, when it was discovered in 1892 it underwent a second bright outburst five months after the first. If Holmes repeats its historical performance, then this comet may offer viewers one more chance to see the show before it bows from the stage.

Source

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PA270005
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Holmes-2007-11-24-18h47m
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17:44 GMT 24th, November 2007.

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The Sun is no longer the largest object in our solar system. The recently visible-to-the-naked-eye Holmes comet has achieved that distinction today. The comet has a larger gas and dust cloud known as the coma, and consequently it has a larger diameter than the sun according to astronomers at the University of Hawaii. Scientists don't seem to have a guess as to how big it will ultimately become.
The Holmes coma's diameter on Nov. 9 was 1.4 million kilometres, based on measurements by Rachel Stevenson, Jan Kleyna and Pedro Lacerda of the University of Hawaii Institute for Astronomy.

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