Cometary orbits revealed something previously unknown – a mirror ecliptic that is inclined to the planetary ecliptic.
Of the National Astronomical Observatory of Japan
An examination of cometary movements shows that the solar system has a second plane of alignment. The analytical study of the orbits of long-period comets shows that the aphelias of the comets, the point at which they are furthest from the Sun, fall either near the known ecliptic plane on which the planets are located or a newly discovered " Empty “ecliptic. "This has important implications for models of how comets originally formed in the solar system.
Artist's impression of the proliferation of long-term comets. The converging lines represent the paths of the comets. The ecliptic plane is shown in yellow and the empty ecliptic in blue. The background grid represents the plane of the Galactic Disk. (Image credit: NAOJ)
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 like comets. Comets, particularly long-period comets that take tens of thousands of years to complete each orbit, are not limited to the area near the ecliptic. They come and go in different directions.
Models of the formation of the solar system suggest that even long-period comets originally formed near the ecliptic and were later scattered into the orbits observed today through gravitational interactions, especially with the giant gas planets. But even with planetary scattering, the aphelion of the comet, the point at which it is farthest from the sun, should remain near the ecliptic. Other external forces are required to explain the observed distribution. The solar system does not exist in isolation; The gravitational field of the Milky Way Galaxy, in which the solar system is located, also exerts a small but not insignificant influence. Arika Higuchi, Assistant Professor at the University of Occupational and Environmental Health in Japan and previously a member of the NAOJ RISE project, studied the effects of galactic gravity on long-period comets by analytically examining the equations for orbital motion.
It showed that the aphelia of long-period comets tends to cluster around two planes, taking galactic gravity into account. First the well-known ecliptic, but also a second “empty ecliptic”. The ecliptic is inclined by about 60 degrees in relation to the disk of the Milky Way. The empty ecliptic is also tilted 60 degrees, but in the opposite direction. Higuchi calls this the “empty ecliptic”, which is based on mathematical nomenclature and initially contains no objects and is only later populated with scattered comets.
Higuchi confirmed their predictions by cross-checking with numerical calculations, some of which were performed in the PC cluster of the NAOJ's Center for Computational Astrophysics. A comparison of the analysis and computation results with the data for long-term comets listed in NASA's JPL Small Body Database showed that the distribution had two peaks near the ecliptic and the empty ecliptic, as predicted. This is a strong indication that the formation models are correct and that long-period comets are forming on the ecliptic. However, Higuchi warns:
“The sharp points are not located exactly in the ecliptic or in the empty ecliptic planes, but in their vicinity. An examination of the distribution of the observed small bodies must consider many factors. A detailed study of the distribution of long-term comets will be our future work. The Legacy Survey of Space and Time (LSST) all-sky project will provide valuable information for this study. "
These results appeared as Arika Higuchi, “Anisotropy of Long Period Comets Explained by Their Formation Process,” published online in the Astronomical Journal on August 26, 2020.