The James Webb and Hubble space telescopes detected 27 small bodies located beyond Neptune, classified as Trans-Neptunian Objects (TNOs). All these objects have a diameter of less than 40 kilometers, with the smallest measured at only 10 kilometers.
This finding surprised scientists because even the smallest bodies show traces of their original formation, despite the collisions that occurred over time, which should have modified their surfaces.
TNOs orbit the Sun in a region very distant from Neptune. Some of these objects originated in this area during the early stages of the Solar System, as small fragments that did not reach the necessary size to become planets.
Previous models suggested that these objects would have suffered numerous impacts from other bodies, which should result in the mixing of surface material, altering its composition and tone. However, the telescopes revealed that the smaller TNOs retain characteristics that seem to preserve information about their origin.
It is noteworthy that the smaller objects are, in a way, retaining the memory of their creation process.
Details on Object Groups
Two distinct groups were identified among the observed objects. Those called dynamically cold follow orbits that are nearly circular and aligned with the plane of the Solar System, considered relatively well-preserved since the time of their formation.
The dynamically hot ones presented a different trajectory. These bodies formed between Uranus and Neptune but were subsequently ejected to more distant regions due to gravitational interactions that occurred during the growth of these planets. Their orbits became more elongated and inclined.
Even after traveling this path, they still exhibit signs of their origin. David Trilling, from Northern Arizona University, stated that 'These dynamically hot TNOs maintain a signature of where they were born, even though their orbits have been scrambled since then.'
Implications of the Discovery
The discovery suggests several important possibilities. James Webb helped determine the size of the 27 objects. In the visible spectrum, the brightness of a TNO is influenced by the amount of light its surface reflects; therefore, a smaller object with high reflectivity may appear as faint as a larger, less reflective object.
However, when analyzed in the infrared, the brightness depends primarily on the body's size. This characteristic allowed for a more precise estimation of the diameters of the observed TNOs.
The analysis also brought an unexpected result: there are fewer very small objects than predicted by formation models. Despite originating in different areas of the early Solar System, the dynamically cold and hot populations show a similar size distribution.
The detected TNOs are extremely faint, exhibiting a brightness between magnitudes 24.1 and 29.3. The difficulty in visualizing them is comparable, according to the study, to distinguishing a cloud of fireflies on the Moon seen from Earth.
This observation constitutes the deepest survey ever conducted on this little-known region beyond Neptune. The results were published in two articles in The Astronomical Journal, dated September 8th: one focused on color and composition, and another dedicated to the size distribution of TNOs.
