On Sep. 22, 2014 the PanSTARRS team discovered just another comet, this time in the constellation Cetus. Comet C/2014 S2 (PanSTARRS) showed a 20.0 mag coma slightly larger than the adjacent stars and a hint of a tail, pointing westward. It will pass perihelion at the beginning of December 2015, expected to reach magnitude 14-15 (CBET 3989 / MPEC 2014-S125). It should be brighter than 16.0 mag during the time span August 2015 to April 2016, thereby moving through the constellations Cassiopeia, Cepheus, Draco, Ursa Minor, Draco and Ursa Major, thus being a comfortably placed object for mid-European observers.

The comet proved to be an unspectacular object visually, but with an unusual brightness evolution, as can be derived by analyzing 120 observations from 11 members of the German Comet Section and 450 international observations. Following a rapid increase in activity pre-perihelion, the comet's activity decreased only slowly post-perihelion. Between Nov. 10, 2015 and Mar. 1, 2016 it showed an almost constant brightness between 9.1 mag and 9.3 mag and was still at 9.7 mag in mid-April. In mid-July it was estimated at 12.0 mag. The evolution can be best described by the formulae:

Total Brightness and Coma Diameter

After its conjunction with the Sun (at the opening of October 2016) no further observations have been published, indicating that the comet must have experienced a major fading during the period of this invisibility.

The coma diameter showed a long lasting plateau too. Measuring less than 1' at the start of the apparition it increased during the following weeks, measuring 4' at the end of October 2015 and 5' in early December. This value remained almost constant until mid-April 2016. Thereafter it decreased only marginally, measuring 4.5' at the start of July. In absolute dimensions, it increased from 80.000 km at the start of the apparition to 400.000 km in mid-October. This value remained quite constant until mid-April 2016. Thereafter the coma began to swallow again, reaching 700.000 km at the opening of July. The degree of condensation was DC 3 at the start of the apparition, increasing to DC 5 until mid-September 2015. Thereafter it decreased very slowly to DC 4 until end of May 2016 and to DC 2-3 in mid-July. Visually a tail was observable between September 2015 and April 2016, with a maximum length of 8' (1.5 to 2 Mio km). Being oriented to WSW in September, it rapidly turned to ENE during the first half of October, thereafter more slowly to NW until the end of January. At the end of April it was pointing eastwards.

Andreas Kammerer

FGK observations