A NUMERICAL STUDY OF THE INTERACTION BETWEEN 2 COMETARY JETS - A POSSIBILITY OF SHOCK FORMATION IN COMETARY ATMOSPHERES

The interaction between two cometary jets is hydrodynamically investigated in the inner coma of an H2O-dominated comet for the two cases of isolated and surrounded jets. Steady-state solutions of collisions between the two jets are obtained by numerically solving the three-dimensional, time-dependent, coupled hydrodynamic equations for H2O gas and the dust with the single radius of a = 0.01, 0.1, or 1 μm in polar coordinates (r, θ, φ). Shock waves are found to be formed in the region where the two cometary jets collide laterally in the following three cases: the isolated case of pure H2O gas jets; the surrounded case of pure H2O gas jets with a weak background ejection; and the isolated case of dusty H2O gas jets. A shock wave consists of two shock fronts and one compressed layer which is sandwiched between the two fronts. For the isolated pure case, the width of the compressed layer is ∼0.4 km near the nucleus surface, and inside the layer the gas density is enhanced by a factor of ∼10 and the gas temperature by a factor of ∼3, compared with those in the preshock region. The shock-compressed gas can reach as far as r ∼ 100 km without considerable expansion in the θ direction. For the surrounded pure case, a shock wave can be formed when the ratio of the gas densities outside and inside the jets on the surface, nbck/njet ≦ 0.01 (i.e., a weak background ejection). For the isolated dusty case, the density distributions of the medium- and small-sized dust (a ≦ 0.1 μm have peaks in the compressed layer of the gas, where the concentration of the dust becomes larger with decreasing the dust radius. © 1990.