Comet ISON, formally known as C/2012 S1, was a sungrazing comet discovered on 21 September 2012 by Vitaly Nevsky (Виталий Невский, Vitebsk, Belarus) and Artyom Novichonok (Артём Новичонок, Kondopoga, Russia). The discovery was made using the 0. 4-meter (16 in) reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia. Data processing was carried out by automated asteroid-discovery program CoLiTec. Precovery images by the Mount Lemmon Survey from 28 December 2011 and by Pan-STARRS from 28 January 2012 were quickly located. Follow-up observations were made on 22 September by a team from Remanzacco Observatory in Italy using the iTelescope network. The discovery was announced by the Minor Planet Center on 24 September. Observations by Swift in January 2013 suggested that Comet ISON's nucleus was around 5 kilometers (3 mi) in diameter. Later estimates were that the nucleus was only about 2 kilometers (1 mi) in diameter. Mars Reconnaissance Orbiter (MRO) observations suggested the nucleus was smaller than 0. 8 kilometers (0. 5 mi) in diameter.