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Comet ISON may not be intact

    In the last few hours there have been reports that comet ISON may not be intact in one piece.  Our own results at the end of this page. 

(1) On November 25.27 Michael Drahus a radio astronomer from Caltech/NRAO working with the IRAM millimeter radio telescope in Spain, and Israel Hermelo of IRAM/Granada, reported that there had been a consistent rapid fading of the molecular emission of this comet between November 21st and November 25th by at least a factor of 20 or even more.   What is preocupating about this report is that molecular emissions measure the intantaneous activity of the comet, in contrast with visual observations were the cloud of debris can last for days around the nucleus thus masking any fragmentation.

    Radio observations can be made during day or night and are not affected by the solar glare.

(2)  Measurements of production rates and dust from the Trappist telescope in Chile on November 23rd, also show a decrease in activity by a factor of 3, according to Emmanuel Ejehin. 

(3) Nicolar Biver reports that astrometric observations were showing the comet trailing behind the ephemeris.   This could happen if there is a cloud of debris lagging behind  the nucleus.  The nucleus may be non-existent and there would be no way of knowing.   The offset is about 5 arc second, which at the distance of the comet is about 3000 km.

(4) The non-gravitational forces are a measure of how much material is being ejected from the nucleus.  For a long period of time it was not possible to measure the non-gravitational forces. Now they have been measured and the value is larger than for comet LINEAR, a comet that disintegrated, by a factor of x1.1.

(6) Our own results confirm that comet ISON may be in trouble.  We have completed an update of the Secular Visual Light Curve and we are showing it in the Figure 1.  This update includes spacecraft measurements.

Figure 1.  The Visual Secular Light  Curve  of Comet ISON  with data  up to  November 26th.  The absolute magnitude of the comet  was 8.2+-0.1.  There  was an outburst starting on November 14.035,  or R= -0.6486 Afrom the Sun, and the light curve reached a  maximum at  R(MAX)= -0.3726 AU or November 22.25.  The brightness has begun to increase again, but it is following a R^(-2) law characteristic of a reflecting body.  This suggests that comet ISON has stopped releasing volatiles. 

    Two people are making measurements of spacecraft observation, STEREO HI-1A.  They are Man To and M. Knight.  The measurements by Man TO required of a correction of -0.9  magnitudes to bring them to the level of the visual observations.  The measurements of Knight required of a correction of -0.75 magnitudes.

    The new Visual Secular Light Curve shows that the comet is once again increasing in brightness but it is following a R(-2) law characteristic of a reflecting body.  This is the law followed by all asteroids.  This implies that comet ISON has stopped releasing volatiles and it is simply reflecting the solar light as an atmosphereless body.  This would be the case if there were a cloud of dust and debris.  However we still lack visual confirmation of the fragmention. 

    Spacecraft measurement must continue.  If the comet continues exhibiting the R(-2) law, it would be direct proof that it has stopped sublimating volatile and that it is really defunct.

    You can watch comets ISON and Encke moving through space in this movie of Stereo Spacecraft:

http://www.isoncampaign.org/files/images/blogpics/ison_encke_nov19_23_crop_hi1a.gif

     New developments on the comet will be posted as soon as they are available. 


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