Establish the long-term persistence of the TNO colour distribution

Determine whether the underabundance of very red trans-Neptunian objects at high inclinations and high eccentricities persists throughout gigayear-scale Solar System evolution.

Background

Previous work showed that the proposed stellar-flyby scenario can reproduce correlations between TNO colours and orbital characteristics, including the scarcity of very red objects among high-inclination and high-eccentricity populations. That earlier analysis did not follow the system through the full 4.5 Gyr history of the Solar System.

The paper explicitly frames the persistence of this colour pattern under long-term dynamical evolution as an unresolved question. Its own simulations subsequently find that the scarcity is retained after 4.5 Gyr, but the question is stated before that result and concerns whether the feature should persist generally under the model’s long-term evolution.

References

Nevertheless, this analysis did not encompass the full 4.5~Gyr timescale of Solar System evolution. Therefore, a critical question remains: does the underabundance of very red TNOs in these regions of parameter space persist throughout Gyr-scale evolution?

— Trans-Neptunian Object dynamics even better explained by a stellar flyby after 4.5 Gyr of evolution  (2609.03575 - Pfalzner et al., 3 Sep 2026) in Section 5, “TNO colours”