Activity of Comet 29P/Schwassmann–Wachmann 1

•We simulated evolution of the nucleus of Comet 29P/SW1.•The simulations include crystallization of amorphous ice, sublimation of the CO ice and local eruptions.•In polar regions explosions are possible for almost any composition and structure of the nucleus.

Comet 29P/Schwassmann–Wachmann 1 is a continually active object moving along nearly circular orbit at a large heliocentric distance ∼6 AU. The comet is famous for its repeated outbursts. We look for structure and composition of the nucleus that leads to the observed frequent outbursts. We performed series of numerical simulations dealing with evolution of the nucleus, including changes of the structure and of the CO gas pressure. In our model the porous nucleus has layered structure. Outermost layer is composed of grains with nonvolatile cores mantled by crystalline water ice. Deeper the grains have three components: non-volatile cores, amorphous water ice and, the carbon monoxide ice. The simulations include crystallization of amorphous ice in the nucleus, sublimation of the CO ice and local explosions. We have found, that for an equatorial location the explosions can be expected only in special case, when the nucleus is fine grained, fluffy and rich in CO. In polar regions explosions are possible for almost any composition and structure of the nucleus. Explosions can be either single, or multiple.