Astronomers have for the first time confirmed the existence of permanent "Trojan" asteroids following Neptune along its orbit. The discovery is reported in a paper published in The Astrophysical Journal Letters.
Trojans are small celestial bodies that move in the same orbit as a planet but at some distance ahead of or behind it. As early as 1906, entire families of such objects were found at Jupiter. Later, similar groups were found at Saturn and Uranus, but at Neptune they could not be detected for a long time.
The difficulty was that these distant and faint objects have for the past ten years been projected onto a very bright and dense region of the sky - the center of the Milky Way, which prevented them from being seen. Now this cloud has begun to emerge from the zone of interference.
A team led by Dr Meg Schwamb of the Astrophysics Research Centre at Queen's University Belfast analyzed data from early test observations by the Vera Rubin Observatory in Chile. This telescope, with an 8.4-meter mirror and the largest digital camera ever built, began operation in June 2025 and is now conducting a large-scale survey of the southern sky.
It was the high resolution and speed of imaging that made it possible to identify two permanent members of Neptune's "trailing" cloud and one candidate. According to Schwamb, these observations have provided the clearest picture to date of this population and doubled the number of known objects on long-lived orbits.
Comparing images in different filters, the researchers concluded that the surfaces of the asteroids flying ahead of and behind Neptune are similar. Over the next nine years, the Rubin Observatory is expected to discover dozens or even hundreds of such objects, as well as tens of thousands of icy bodies in the Kuiper Belt - the region beyond Neptune where many minor planets are concentrated.
The authors emphasize that these are only the first results, and they show how rich future data may be. However, the conclusions are based on a limited set of observations, and final confirmation of the candidate's status is still to come.