A model of cometary outbursts based on the idea of fragmentation of ice grains

Abstract

In this Letter the mechanism of destruction of ice grains as the cause of cometary outbursts and variations of brightness is reviewed. Such destruction can arise from the combination of two causes: inclusions of chemical compounds that are much more volatile than water‐ice placed inside cometary water‐ice grains; and the influence of the solar wind on such heterogeneous grains. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. This approach gives a simulated increase in the cometary brightness that is consistent with the observed one. It is concluded that this mechanism is a probable and real explanation of the sudden activity of comets at a wide range of heliocentric distances.

The destruction of cometary grains and changes in the luminosity of comets

“…Taking the obtained results into consideration we conclude that the critical heliocentric distance of a comet d cr is increasing function of the parameter f as well as the value of the modulus of the grains electrostatic potential | V |. We can calculate the simulated changes of the cometary brightness in a similar way as in the paper of Gronkowski (2007b). In that paper and references therein numerical problems related to the calculation of the changes in the cometary brightness induced by the grain fragmentation are described in detail.…”

“…Unfortunately as the previous electrostatic destruction this mechanism generally gives small changes in the cometary luminosity and cannot be the source of outbursts in a general way as was shown www.an-journal.org by Gronkowski (2001). Recently (Gronkowski 2007b), it was shown that the cometary grains can undergo simultaneously the electrostatic destruction as well as the thermodynamic fragmentation, and this total fragmentation can be the source of essential changes in the cometary brightness. In some way the presented paper is the development of the above mentioned author's work which was only the qualitative approach to the problem of grain fragmentation.…”

“…The scattering cross-sections are functions of the scattering efficiencies of primary and daughter particles respectively. It should be emphasized that in this paper the numerical values of cometary parameters are assumed to be the same as in the papers by Gronkowski (2007aGronkowski ( , 2007b. In other cases the values of these characteristics are specified in the tables.…”

“…(2) in the paper by Gronkowski (2007b). In order to obtain the heliocentric distance at which the grains undergo destruction we should take into consideration the dependence of the saturated vapour pressure of inclusions on the temperature T (Eq.…”

“…It should be noted that the unexpected activity of comets which manifests as outbursts of brightness is frequently reported for periodic as well as parabolic comets. The outburst of a comet is a rapid increase in its brightness, usually by 1-5 magnitudes within few hours to several days (Hughes 1990(Hughes , 1991Gronkowski 2002Gronkowski , 2007b.…”