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Title: Disintegration of Comet C/2012 S1 (ISON) Shortly Before Perihelion: Evidence from Independent Data Sets
Author: Zdenek Sekanina, Rainer Kracht

As an Oort Cloud object with a record small perihelion distance of 2.7 Rsun and discovered more than a year before its encounter with the Sun, comet C/2012 S1 is a subject of considerable scientific interest. Its activity along the orbit's inbound leg evolved through a series of cycles. Two remarkable events preserved in SOHO's and/or STEREO's near-perihelion images of its tail were an early massive production of gravel at heliocentric distances of up to ~100 AU(!), evidently by the annealing of amorphous water ice on and near the nucleus' surface; and, about a week before perihelion, a rapid series of powerful explosions, from the comet's interior, of water with dust at extremely high rates, causing precipitous fragmentation of the nucleus, shattering it into a vast number of sublimating boulders, and ending up, a few days later, with a major, sudden drop in gas emission. The disintegration of the comet was completed by about 3.5 hours before perihelion, at a heliocentric distance of 5.2 Rsun, when C/2012 S1 ceased to exist as an active comet. The orbital motion in this period of time was subjected to progressively increasing outgassing-driven perturbations. A comprehensive orbital analysis results in successfully fitting the comet's observed motion from 2011 to ~7 hours before perihelion.

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Title: Molecular observations of comets C/2012 S1 (ISON) and C/2013 R1 (Lovejoy): HNC/HCN ratios and upper limits to PH3
Author: M. Agundez, N. Biver, P. Santos-Sanz, D. Bockelee-Morvan, R. Moreno

We present molecular observations carried out with the IRAM 30m telescope at wavelengths around 1.15 mm towards the Oort cloud comets C/2012 S1 (ISON) and C/2013 R1 (Lovejoy) when they were at 0.6 and 1 AU, respectively, from the Sun. We detect HCN, HNC, and CH3OH in both comets, together with the ion HCO+ in comet ISON and a few weak unidentified lines in comet Lovejoy, one of which could be tentatively assigned to methylamine (CH3NH2). The monitoring of the HCN J = 3-2 line showed a tenfold enhancement in comet ISON on November 14.4 UT due to an outburst of activity whose exact origin is unknown, although it could be related to some break up of the nucleus. The set of CH3OH lines observed was used to derive the kinetic temperature in the coma, 90 K in comet ISON and 60 K in comet Lovejoy. The HNC/HCN ratios derived, 0.18 in ISON and 0.05 in Lovejoy, are comparable to those found in most previous comets and are consistent with an enhancement of HNC as the comet approaches the Sun. Phosphine (PH3) was also searched for unsuccessfully in both comets through its fundamental 1-0 transition, and 3sigma upper limits corresponding to PH3/H2O ratios 4-10 times above the solar P/O elemental ratio could be derived.

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Subaru Telescope Detects Rare Form of Nitrogen in Comet ISON

A team of astronomers, led by Ph.D. candidate Yoshiharu Shinnaka and Professor Hideyo Kawakita, both from Kyoto Sangyo University, successfully observed the Comet ISON during its bright outburst in the middle of November 2013. Subaru Telescope's High Dispersion Spectrograph (HDS) detected two forms of nitrogen--14NH2 and 15NH2--in the comet. This is the first time that astronomers have reported a clear detection of the relatively rare isotope 15NH2 in a single comet and also measured the relative abundance of two different forms of nitrogen ("nitrogen isotopic ratio") of cometary ammonia (NH3). Their results support the hypothesis that there were two distinct reservoirs of nitrogen the massive, dense cloud ("solar nebula") from which our Solar System may have formed and evolved.
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Zomet C/2012 S1 (ISON) makes its closest approach to the Earth (0.429 AU) on the 27th December 2013



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Comet Ison 'vaporised' in Sun pass

Comet Ison seems to have been destroyed in its encounter with the Sun.
Astronomers saw the giant ball of ice and dust disappear behind the star, but then fail to emerge as expected.

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Comet C/2012 S1 (ISON) is at perihelion (0.013 AU) on the 28th November 2013.



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Comet C/2012 S1 ISON is 1 from Comet Encke, and 5 from Saturn and Mercury in the dawn sky on November 24, 2013.

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Comet ISON is 5.5 from Mercury on the 22nd November, 2013.

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Comet C/2012 S1 (ISON) lies 0.7 from the star Spica on the 18th November 2013.



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Comet C/2012 S1 (ISON) will pass ~3 from M95, M96 and M105 in the constellation Leo on the 26th October, 2013.

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