A model of cometary outbursts: a new simple approach to the classical question

Abstract

Cometary outbursts, i.e. a sudden increase in brightness, have aroused astronomers’ curiosity since the 1920s (Hughes). In 1927, Comet 29P/Schwassmann–Wachmann 1 was discovered, probably at the maximum of one of its outbursts. Many authors have tried to explain the source of cometary outbursts. They formed various models and hypotheses, but none of them have been definitely confirmed and generally accepted. In the present article, we propose a new model for the outburst activity of comets. This model is based on an idea of Ipatov & A'Hearn. This idea is a conclusion from the analysis of time variations in velocity of particles ejected from Comet 9P/Tempel after collision with the Deep Impact impactor. According to this, there are large cavities a few metres below the surface of comet nuclei. These cavities contain material under high gas pressure. In suitable conditions, the surface layers over the cavities can be thrown away and the deeper layers of the nucleus exposed. Finally, an outburst of the comet may be observed. The possible scenario in terms of outbursts is given. The amplitude of the jump in comet luminosity is also calculated. Numerical simulations were carried out for a wide range of cometary physical parameters, which are suitable for comets belonging to the class of Jupiter-family comets. They provide values of jumps in comet brightness that are consistent with those observed during the outbursts of many comets.