Color variations of comet 29P/Schwassmann–Wachmann 1 in 2018

Abstract

We measure the photometric color in the inner coma of Comet 29P/Schwassmann–Wachmann 1 on nine nights in August and October, 2018. We see variations in the color slope from S′=(19.72±1.72)% per 0.1μm to S′=–(6.88±1.72)% per 0.1μm. The blue color is accompanied with increasing brightness suggesting that it is caused by mild outburst activity. We model the extreme values of S′ using agglomerated debris particles. The reddest color suggests a coma dominated by Fe–Mg silicate particles or organic particles obeying a differential power-law size distribution with power index n≈2.6±0.3. The bluest color is indicative of a high abundance of either water–ice having a power index n≤2 or Mg-rich silicate particles having n≈2.5±0.3. From these properties we compute an instantaneous dustload of the inner coma ranging from as low as 1450±150m3 when there was sporadic activity to 5,900—26,300m3 when there was mild activity. Such a dustload is one-two orders of magnitude larger compared to other comets. We perform simulation of the dust motion within the coma to estimate the number of particles leaving our aperture to constrain the dust production rate. We find a dust production rate of Qdust≈4.6±2.3kg/s during the quiescent period, and Qdust≈17.6±2.8 kg/s during a mild outburst. Such values appear at the lower limit of what has been calculated previously.