A study of comet motions indicates that the solar system has a second alignment plane. Analytical investigation of the orbits of long-period comets shows that the aphelia of the comets, the point where they are farthest from the Sun, tend to fall close to either the well-known ecliptic plane where the planets reside or a newly discovered “empty ecliptic.” This has important implications for models of how comets originally formed in the solar system.
In the solar system, the planets and most other bodies move in roughly the same orbital plane, known as the ecliptic, but there are exceptions such as comets. Comets, especially long-period comets taking tens-of-thousands of years to complete each orbit, are not confined to the area near the ecliptic; they are seen coming and going in various directions.
The solar system does not exist in isolation; the gravitational field of the Milky Way galaxy in which the solar system resides also exerts a small but non-negligible influence
hen the galactic gravity is taken into account, the aphelia of long-period comets tend to collect around two planes. First the well-known ecliptic, but also a second “empty ecliptic.” The ecliptic is inclined with respect to the disk of the Milky Way by about 60 degrees. The empty ecliptic is also inclined by 60 degrees, but in the opposite direction. Higuchi calls this the “empty ecliptic” based on mathematical nomenclature and because initially it contains no objects, only later being populated with scattered comets.