Neptunian Trojans are trans-Neptunian objects in 1:1 mean-motion resonance with the ice giant Neptune. These asteroids are generally thought to have been captured from the ancient protoplanetary disk into co-orbital resonance with Neptune during its outward migration. It is possible, therefore, that the color distribution of Neptunian Trojans is a constraint on the location of any color transition zones that may have been present in the protoplanetary disk. In support of this possible test, planetary scientists from NASA and elsewhere obtained new observations of 18 Neptunian Trojans, more than doubling the sample of Neptunian Trojans with known visible colors to 31 objects.
The newly-observed Neptunian Trojans are between 50 and 100 km in size and are located at a distance of around 4.5 billion km from the Sun.
Asteroids orbiting this far away are faint and so are challenging for astronomers to study.
Before the new work, only 13 Neptunian Trojans had been studied, requiring the use of some of the largest telescopes on Earth.
The new data were gathered over the course of two years using the WASP wide field camera on the Palomar Observatory telescope, the GMOS cameras on the Gemini North and South telescopes, and the LRIS camera on the Keck telescope.
Of the 18 observed Neptunian Trojans, several were much redder than most asteroids, and compared with other asteroids in this group looked at in previous studies.
Redder asteroids are expected to have formed much further from the Sun; one population of these is known as the Cold Classical trans-Neptunian objects found beyond the orbit of Pluto, at around 6 billion km from the Sun.
The newly-observed Neptunian Trojans are also unlike asteroids located in the orbit of Jupiter, which are typically more neutral in color.
The redness of the asteroids implies that they contain a higher proportion of more volatile ices such as ammonia and methanol.
These are extremely sensitive to heat, and can rapidly transform into…
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