Researchers using the Subaru Telescope found that small Jupiter Trojan asteroids lack the distinct color split seen in larger ones.
Why the color divide disappears in smaller Trojans
The study examined 44 small Trojans between 3 km and 16 km in diameter, finding they reveal a continuous range of colors instead of separating into red and less-red groups. This contrasts with larger Trojans, which clearly split into D-type (redder) and P-type/C-type (less red) asteroids. Researchers attribute the difference to surface processes like collisions and fragmentation that may blur original compositional differences over time. The smaller asteroids’ rapid spin made observation challenging, requiring fast filter changes to capture accurate data.
How the team overcame observational challenges
Researchers used the last run of Suprime-Cam on the 8.2m Subaru Telescope in Hawai’i, leveraging its ability to change filters quickly. This was critical because smaller asteroids rotate rapidly, and slower filter changes would have captured shifting sides during observation, skewing results. By cycling through two filter changes in under an hour, they averaged out rotational effects to receive reliable spectrographic profiles. The method allowed unbiased sampling of 44 objects from an initial pool of 120 candidates.
What this means for solar system history
The findings suggest that the earliest solar system record among Trojans may be more complex than previously thought, with surface evolution erasing early compositional splits in smaller bodies. Larger Trojans still show the bimodal color split, hinting that size influences how well primordial traits are preserved. Scientists now question whether the color-coding in larger asteroids reflects original formation conditions or later evolutionary sorting. No follow-up timeline or instrument upgrades were mentioned in the source.
Why did researchers focus on smaller Trojans?
They aimed to solve the mystery of why larger Trojans split into red and less-red groups by checking if the pattern held at smaller scales.
What instrument made this observation possible?
The Suprime-Cam on the Subaru Telescope, due to its fast filter-changing speed needed to counteract rapid asteroid rotation.