2017s3 20180703 dbamberger

Comet C/2017 S3 (PANSTARRS) in outburst, 44 days before perihelion

This comet was reported by Michael Jäger on July 1st to be in outburst. It has brightened by over 2 mag since our last observation (June 26th, see https://goo.gl/wdFF4h), which itself was over 2 mag brighter than it had been in early June.

C/2017 S3 will come to perihelion in August, only 0.2 AU from the Sun. This outburst happened when the comet was still far from perihelion. It is likely caused by breakup of the nucleus, making it unlikely that the comet will survive its perihelion passage. Before the outburst, it was expected to brighten rapidly, possibly reaching 6-7 mag by the end of July.

2018 07 03.05 UT
Photometry (APASS V magnitude unfiltered, 230" aperture radius): m1 = 11.2 +/- 0.1 mag
Nuclear magnitude (Gaia G magnitude unfiltered, 8" aperture radius): m2 = 13.9 +/- 0.1 mag
Highly condensed inner coma 0.3 arcminutes in diameter, possibly elongated in PA 300°
Outer coma 3.9 arcminutes in diameter, circular

Comet altitude 34°, elongation 52° from the Sun. Interference from 80% illuminated Moon at a distance of 92°, and from twilight (Sun 14° below horizon).