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J. J. Matese (University of Louisiana at Lafayette), J. J. Lissauer (NASA ARC)
For an Oort cloud comet to be observable as a new comet, its perihelion must be moved from a point external to the loss cylinder boundary to a point internal to observable limits in a single orbit. The galactic tide can do this in a continuous manner. Near-parabolic comets, with specific angular momentum H\propto \sqrt q, will most easily be made observable. Therefore, to reduce the perihelion distance, H must decrease. Since weak perturbations are, in general, more numerous than strong perturbations, we can anticipate that comets made observable by a weak tidal torque will more likely be observed when their slowly changing perihelion distances are approaching their minimum values rather than receding from their minimum values. That is, defining \Delta {\vec H}tidal as the change due to the galactic tidal torque during the prior orbit, the sign S\equiv {\rm Sign}({\vec H}obs \cdot \Delta {\vec H}tidal) will more likely be -1 than +1 if a weak galactic tidal perturbation indeed dominates in making comets observable. Using data of the highest quality class (1A), we find that 49 comets have S=-1 and 22 have S=+1, which has a binomial probability of 0.0009 that as many or more would exhibit this characteristic if in fact S=±1 were equally likely. We further find that the preponderance of S=-1 correlates with weakly perturbed (tightly bound) comets in a statistically significant manner. This is strong evidence that the data are of sufficiently high quality and sufficiently free of observational selection effects to detect this subtle imprint of the tide.\\ \em{J.J.L. received support from Planetary Geology and Geophysics Grant 334-30-50-01}
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.