The effects of passing stellar encounters on planet formation and implications to formation of dust debris disk around main sequence stars

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Stars are generally formed in clusters. Since their spatial density is high, stars in clusters experience close concounters with each other until the clusters are broken up on timescales of 10^8-10^9 years. In such initial stages, planets are likely to be being formed and be affected by the stellar encounters. We have investigated the effects, in particular, suggested that the orbital distribution of Keiper belt objects show signature of such encounters. Through numerical calculations, we showed that a star passing through about 100 AU from the Sun can be responsible for the highly eccentric orbits of current Keiper belt objects at 40-47 AU and inhibit formation of large planets beyond 30 AU, which is consistenet with present Solar system. Beyond 30 AU, collisions of planetesimals result in disruption rather than accretion, resulting in formation of a dust debris disk. Similar dust production processes would occur also in extrasolar planetary systems. Observations show that dust debris disks exist beyond 30 AU from central stars. Our result is consistent with the observations. We have presented these results at DPS meetings of American Astronomical Society a few times, and published two related papers in DPS' s journal "Icarus" and submitted another two papers.