Home=Current Comets
| The German Group
| Tutorials
| Archive: C/2017 S3
| Projects, publications
| Images
| Contact
On Sep. 23, 2017 the PanSTARRS team discovered a comet of magnitude 21 in the constellation Draco. Combinig the images with additional ones of Aug. 17 the orbit could be quickly determined. Comet C/2017 S3 (PanSTARRS) will pass perihelion on Aug. 15, 2018 in the solar distance of only 0.21 AU. Observations during the following days showed a rather diffuse 8" coma of total magnitude 20.8 (CBET 4432). This yields a preliminary absolute magnitude of 10.0 (assuming an activity parameter of n=4). This absolute magnitude is below the Bortle limit. Consequently, it is rather probable that this comet will extinguish while approaching the Sun. In the case it will develop according to the values mentioned and will survive it will peak at 3 mag at perihelion. However, in those days it will be situated very near the Sun. Mid-European observers can follow the comet until the start of August in the morning sky. It should get brighter than 16 mag at the opening of May 2018, getting brighter than 10 mag in mid-July. In the days it will disappear in the twilight it should be of magnitude 5-6. During the mentioned time span it will move through the constellations Cassiopeia, Camelopardalis, Auriga, Gemini and Cancer. Post-perihelion it should reappear in the morning sky during the first week of October, expected to be an object of magnitude 13, reaching magnitude 16 in mid-December. During this period it will drift slowly through the constellation Coma Berenices.
Actually the proximity to the Sun was too much for the comet. However, it did not intend to exhaust silently, instead it wanted to show its bright side. According to 106 observations from 38 observers the comet showed a rapid brightening at first, from 13.0 mag on June 26 to a first maximum of 9.1 mag on July 4. This was followed by a decrease in brightness to 10.5 mag until July 11, which was followed by a second rapid brightening, with a maximum of 7.0 mag on July 20. Thereafter the comet faded rapidly, reaching 10.5 mag on July 25, when the continuous surveillance ended. Of course no useful formula can be applied to describe this behavior. Last observations date from Aug. 2, when the faint and diffuse comet was situated in the twilight low above the northeastern horizon, making estimates very difficult.
Total Brightness and Coma DiameterComa diameter and degree of condensation mimicked the brightness development: The coma diameter increased from 1.5' (100.000 km) to 5.5' (350.000 km) on July 4, only to decrease again, reaching 3.0' (175.000 km) on July 13. Thereafter another increase took place with the diameter peaking at 7' (350.000 km) on July 20. On July 25 the coma diameter was estimated at 4' (175.000 km). The degree of condensation reached DC 3-4 during the first brightness maximum, thereafter decreased to DC 2, only to increase to DC 5-6 until July 20. Following that it decreased rapidly again, reaching DC 3 on July 25. At the time of maximum brightness a tail of 0.6° (2 Mio km) length was visually observed, pointing WNW.
Andreas Kammerer