What’s up with the Kuiper Belt?

Alexandre Daigneault


It is innate to human nature to be curious, whether in understanding itself or creating new technologies, including understanding the past. Some researchers (read: curious people) investigate as far as the beginning of the universe, while others focus on the development of the Earth and its family, the Solar System.

One not so well-known element of our Solar System has been under investigation over recent decades: the Kuiper Belt, a large group of mostly small bodies orbiting beyond Neptune. The first Kuiper Belt Objects, or KBOs, other than Pluto and its moon Charon, were discovered in the 1990s. The orbital structure of the Kuiper Belt is very different from the planets (who are all within the same plane and have circular orbits) and, in general, from what is expected from simply evolving from the initial protoplanetary disk (a large disk of dust that used to orbit the Sun ) which originated most objects in the Solar System.

In order to explain the particular orbital structure of the Kuiper Belt, researchers run various computer simulations, some of which evolve over billions of years, to see what initial conditions reproduce the observations in reality. For example, the inclination of the orbit of KBOs is found to limit the speed at which Neptune is expected to have migrated from where it initially formed to its current distance from the Sun.

One not yet perfectly understood characteristic of the Kuiper Belt is its colour-inclination correlation. The Canadian-led Outer Solar System Origins Survey (OSSOS)’s observations support even more strongly that there is a correlation between the colour of the KBOs and their orbit inclination. Furthermore, their observations support for the first time that this correlation is applicable to every subpopulation within the Kuiper Belt.

Researchers at the Université de Montréal are currently investigating this correlation. The investigation’s hypothesis suggests that the color corresponds to the KBO’s chemical composition, and that the chemical composition in turn corresponds to the initial distance from the Sun at which the object formed. Their simulations seem to support this hypothesis. Their inquiry is currently analyzing the exact mechanisms involved, since the main identified mechanism, the Kozai mechanism, mostly only applies to one specific subpopulation of the Kuiper Belt called the resonant objects.

Positive conclusion to their research would very strongly support a chemical composition gradient in the Solar System billions of years ago, as well as being a significant step in understanding the development of the Kuiper Belt.

Originally Published on www.bandersnatch.ca Vol.49 Issue 13 on April 15th, 2020