In an article in the journal Icarus, we have suggested that there is statistically significant evidence that this concentration, amounting to an excess of approximately 25%, could be caused by a companion to the Sun which aids the galactic tide in making Oort cloud comets observable. The companion is estimated to have a mass of 3-5 MJupiter and a mean distance at the interaction site of 25000 AU. If there is no substantive inner Oort cloud, a closer orbit is possible. Its location along the great circle is not presently predictable and that will present a problem for detection, but it is potentially observable in the radio using the VLA and should also be observable in the infrared at 5 microns using the next generation of space telescopes such as Spitzer and SOFIA. An object with these properties would be readily seen by WISE (Ned Wright's Wide-Field Infrared Survey Explorer), recently approved for a 2008 launch in NASA's Medium-class Explorer program of lower cost, highly focused, rapid-development scientific spacecraft. The estimated mass of the companion puts it below the nominal brown dwarf limit (~ 13 MJupiter ) where deuterium fusion can occur and would make it a planet in that context. However its location in the outer Oort cloud means that it is not possible that it formed in the protosolar planetary disk. The object could have been ejected from another stellar system and captured by the Sun in their complex star forming region.
At the Berlin meeting of "Asteroids, Comets, Meteors 2002" (co-authored by Jack J. Lissauer, link to paper below) we have presented supportive evidence of the solar companion conjecture. Since the Icarus paper was published twenty seven new outer Oort cloud comets have been discovered. The previously noted overpopulated band maintains an excess. This strengthens the statistical evidence for correlated orbital elements as predicted by the analysis. The figure below includes the best fit perturber orbit and can be compared to the corresponding figure in the 1999 Icarus paper which did not include the new data. It is argued that the correlated data found is highly unlikely to be the result of "bad data" - which typically reduces real correlations. Nor is it likely to be spuriously produced by some unspecified "observational selection effect" - a situation where limitations on our ability to observe comets can spuriously affect the distributions of the observed data. To date, the only documented observational selection effect applicable to this data is the well-known one that comets with large perihelion distances are less likely to be sufficiently well observed so that their energies (i. e. semimajor axes) are accurately known. We discuss in these papers why this selection effect will tend to spuriously reduce the predicted correlations rather than enhance them. A recent paper ("Biases in Cometary Catalogues and Planet X", J. Horner and N. W. Evans, MNRAS 335 (3) 641, (2002)) has concluded that a bound Jovian mass companion is a "possible, perhaps even likely, explanation of the unusual pattern".
