Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
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18. The Oort Cloud
18. The Oort Cloud
Pages 246-258
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MUKHIN, AND ROALD Z SAGDEEV Institute of Space Research ABSTRACT Views of the large-scale structure of the solar system, consisting of the Sun, the nine planets and their satellites, changed in 1950 when Oort (Oort 1950)
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However, the mean mass of a typical "new" comet must also be estimated using direct observations, without extrapolation in the region of small dimensions and comet nucleus masses. Direct observations of 14 bare nuclei of long-period comets (i.e., observations at great heliocentric distances)
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The closeness of the mean spectrum value < MA > to the mean observed value MA is understandable in this case (as opposed to the case where the effects of observational selection are taken into account)
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Naturally, this must produce radical cosmogonic consequences. We will note that this circumstance was first noticed by Weissman (1986~.
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(7) Therefore, the mean mass of LP-comets can only be an order greater than the mean current mass of SP-comets on the condition that ALP ~ ASP.
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. HILL'S CLOUD MASS It has currently been deemed likely that the canonical Oort cloud is only a halo surrounding a dense, internal cometary cloud.
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ANGULAR MOMENTUM DISTRIBUTION IN THE SOLAR SYSTEM If the Hills and Oort clouds are truly as massive as follows from the above estimations, then: (1) comet formation could hardly have occurred in the Uranus-Neptune zone, as is frequently considered, since as such a large mass was ejected to the periphery of the solar system, the planets should have moved considerably closer to the Sun (Marochnik et al.
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(1988) the Oort cloud's angular momentum can be written as JO = 4/3Mo(GM(3~m~n)
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Since it is apparently nonthermalized, its angular momentum Jcore is equal to (Marochnik et al. 1989~: we find: Jcore = 2Mcore[GM(3ctc in(1—e2~/2~1 + tic }/2~-i, (16)
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FIGURE 2 Histogram of the probable distribution of angular momentum in the solar system. A cometary system with a total angular momentum of EJplanet = 3~105° is located in the region of heliocentric distances of r < 40 AU.
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Attempts to make some stronger assertions would be too speculative at this point. CONCLUSION Assuming as typical for long-period comets the albedo value of Halley's comet, we come to the conclusion that the Oort cloud must be extremely
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ACKNOWLEDGMENT We are deeply grateful to Alan Boss and Paul Weissman for their important comments, and to Vasilii Moroz and Vladimir Strel'nitskii for their insightful discussion, and to Georgii Zaslavskiy for his input regarding individual aspects of this study. REFERENCES Allen, C.W.
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1987. Consequences of the size determination of p/Halley by space probes on the scale of sizes of cometaIy nuclei.
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