Mathematics – Probability
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19410701r&link_type=abstract
American Astronomical Society Meeting 194, #107.01
Mathematics
Probability
Scientific paper
The total mass of the Kuiper-belt objects is presumably much smaller than mass of solid material which would be expected in this region if the surface density continued beyond the Neptune's orbit ~ r(-3/2) . It was suggested that the surface density in the solar nebula continued monotonically far beyond Neptune's orbit, and a number of 1000 km bodies have been formed there, however they destroyed each other later. In this paper, I analize few alternative processes which can explain properties of the Kuiper belt and include into the formation of the Oort cloud. First, the surface density in the solar nebula can drop beyond several tens AU by several times because of an additional torque, generated by the magnetic field at a peripheral parts of the solar nebula which are transparent for galactic cosmic rays - the major sources of gas ionization. Slow accumulation at the periphery of the solar system increases also a chance that it is interrupted by close encounter with another star. The probability of the passage of the star at several hundreds AU is rather small in the present-day environment of the solar system. However it has been significant during its early history, if the solar system has been formed in a relatively dense star-forming region, like Rho Oph. Close encounter can dynamically heat the outer region of the protoplanetary cloud and switch the accumulation by the destruction, even if the distance of the closest approach has been remarkably larger than the heliocentric distance. Planetesimals located closer to the stellar path than to the Sun can be ejected from the solar system, and at larger distances send onto highly eccentric orbits. These orbits gradually decrease eccentricities with the increasing of semimajor axis due to the tidal effect of distant stars and the planetesimals can join the Oort cometary cloud. These Oort cloud objects had never been at planetary distances. They may contain highly volatile ices which have been frozen on dust grains in dense cores of molecular clouds and have high excess of heavier isotopes, e.g. deuterium. Precise comparison between abundance of these species, can determine if external perturbations of the early solar system played a role in the formation of the Oort cloud or it consists of objects ejected from the region of giant and outer planets, in accordance Oort's hypothesis. Also I will discuss a new idea about possible origin of the commensurability between orbital periods of Kuiper-belt objects and Uranus and Neptune. These objects can be formed of planetesimals captured into resonances as they migrated inward due to the gas drag.
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