Showing papers by "Shin Yabushita published in 1991"
TL;DR: In this paper, the authors examined the hypothesis that the crater formation rate exhibits periodicity by adopting a criterion proposed by Broadbent, which was more stringent than those adopted by previous authors.
Abstract: The hypothesis that the crater formation rate exhibits periodicity is examined by adopting a criterion proposed by Broadbent, which is more stringent than those adopted by previous authors. Data sets of Alvarez & Muller, Rampino & Stothers and of Grieve are tested. The data set of Rampino & Stothers is found to satisfy the adopted criterion for periodicity with period P = 30 Myr. Again, small craters (D < 10 km) in the data set of Grieve satisfy the criterion even better with P = 30 Myr and 50 Myr, but large craters do not satisfy the criterion.
27 citations
TL;DR: In this paper, the maximum possible acceleration due to out-gassing from cometary nuclei is calculated for H2O and CO(N2) molecules, and it is found that the maximum excess velocity at great distance is 0.18 km s−1.
Abstract: Maximum possible acceleration due to out-gassing from cometary nuclei is calculated for H2O and CO(N2) molecules. It is found that the maximum excess velocity at great distance is 0.18 km s−1 so that excess velocities less than this value are compatible with the non-gravitational acceleration due to non-symmetric out-gassing. On the other hand, Comet 1975q and comet 1955V have excess velocities 0.81 and 0.80 km s−1 respectively. These comets may be regarded as the candidates for possible interstellar comets.
8 citations
TL;DR: In this paper, the flux of comets with semimajor axes ∼20000 AU in the outer planetary region is estimated on the assumption that the major planets and the galactic tide control the dynamics of the comets, and the flux is found to be a rapidly increasing function of q, the perihelion distance.
Abstract: The flux of comets with semimajor axes ∼20000 AU in the outer planetary region is estimated on the presumption that the major planets and the galactic tide control the dynamics of comets. The flux is found to be a rapidly increasing function of q, the perihelion distance. If the lifetime of short-period (SP) comets is typically 2 × 10 4 yr, it would be possible to regard SP comets as originating from the Oort cloud. If, however, it is as short as 2 × 10 3 yr there is a discrepancy of a factor 10 between the observed and predicted supply rates.
4 citations