New results from a survey of trans-Neptunian objects which help to further our understanding of these remote icy bodies have been revealed at the National Astronomy Meeting in Manchester. 

There are many small rocky and icy bodies that wander through our Solar System. Some of these are located relatively close to Earth, in the asteroid belt between Mars and Jupiter. Others are located beyond Neptune, giving them the name trans-Neptunian objects (TNOs) or Kuiper Belt Objects (KBOs).

Using the 4.2 metre William Herschel telescope on La Palma, in the Canary Islands, Pedro Lacerda and the “TNOs Are Cool” team made infrared observations of more than 100 TNOs. By combining several images of one TNO into a single image, they were able to acquire measurements that are more sensitive than those by NASA’s Spitzer Space Telescope. However, adding the lower-wavelength Spitzer data to the Herschel observations allowed the team to model the brightness of the TNOs.

Their sample of TNOs mainly included three different classes of objects; Classical KBOs, Plutinos, and Scattered disk objects. The Classical KBOs are the “normal” ones of the bunch and have almost circular obits.

The Plutinos are in what is known as a 3:2 resonance with Neptune, and their name stems from the fact that the dwarf planet Pluto is located among them. A 3:2 resonance means that for every three orbits of the Sun that Neptune does, a Plutino will do two. Lastly, the Scattered disk objects are the furthest from the Sun and are on highly elliptical and inclined orbits.

Lacerda revealed that the brightness, known as albedo, of all three classes is very similar and that most TNOs have quite a low albedo. In addition, the size distribution of all three classes of objects is similar.

The team also searched for any trends which might exist among the TNOs and discovered that larger Classical objects tend to have lower albedos and smaller Classical objects have lower inclinations than the rest of their class. Lacerda and his colleagues also found that there is no correlation between the colour of the object and its brightness.

Lacerda added that the Classical objects seem to be the most “well behaved” as simulations of the formation of the Solar System show that they most likely formed in their current location. In contrast, Plutinos and Scattered objects would have originated elsewhere before the turbulence in the unsettled early Solar System flung them to their current orbits.