C/2012 S1 (ISON)

DISINTEGRATED

Type: Hyperbolic Perihelion date: 28 November 2013 Perihelion distance (q): 0.01 Aphelion distance (Q) : n/a Period (years): n/a Eccentricity (e): 1.00 Inclination (i): 62.2 JPL orbit diagram COBS lightcurve An 18th magnitude comet was discovered with the 0.4-m f/3 reflector of the International Scientific Optical Network (ISON) at Kislovodsk Observatory, Russia, by observers Vitali Nevski and Artyom Novichonok . The preliminary orbit allowed pre-discovery detections from the Mt Lemmon survey in December 2011 and Pan- STARRS in January 2012. It passed within 0.1 AU of Mars on 3 October 2013 and is a Sun-skirting comet. Gareth Williams notes on MPEC 2012-T08 that the "original" and "future" barycentric values of 1/a are (1/a)_orig = +0.000058, (1/a)_fut = +0.000008. The small "original" value suggests that this comet has not made a previous visit to the inner solar system, and is a "new" comet from the Oort cloud. The comet emerged from solar conjunction in September 2013 as an 11th magnitude object in the morning sky. By early October it had brightened to 10th magnitude, but it was clear that the comet was not brightening very quickly. Reports on 6 November suggested a possible increase in brightness and change in appearance, however nothing further developed. Tail rays did form, but this was a solar effect. A tail disconnection event occurred on 13 November. Dynamical tail activity is likely to increase as the comet approaches the Sun and these effects should not be confused with activity on the comet nucleus. Professional observers suggested a rapid increase in gaseous output between 12 and 13 November. The comet became more active on 14 November, developing a near stellar appearance and reaching magnitude 6. It brightened further to 5th magnitude by 15 November, then remained near this brightness according to ground based observers. German scientists suggest that the 12 to 14 November sequence was caused by a minor fragmentation event, which also created coma wings. General tail activity also increased, with a disconnection event seen on 13 November, but there is a risk of confusing solar effects with events on the comet nucleus. Its absolute magnitude was close to or fainter than the Bortle survival limit, and the comet did not survive long after perihelion. The comet entered the SOHO C3 field on 27 November and continued brightening until some 12 hours prior to perihelion, when it was around -2. It then faded. It showed two tails, the longest over 4 degrees long. It was also visible in the STEREO H1A field. The brightest portion of the comet became elongated. A tail feature survived perihelion in the C2 field, and then the comet reappeared as a bright, well condensed object in the C3 field on 29 November. On November 30 the comet appeared very diffuse and significantly fainter in the C3 field and this progressed further as the comet left the field. The transit through the C3 field is shown in this movie. A possible explanation is that the intense solar wind and radiation when very near the Sun stripped all material from the nucleus, causing the fade. As the thermal wave penetrated the bare nucleus it disintegrated, leaving a ghostly remnant. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 12-Mar-13 16.15 0.02 15.7 0.4