De Troianis: The Trojans in the Planetary System

Trojan objects are minor bodies having stable orbits in the L4 and L5 Lagrangian points of a planet. Mars, Jupiter, and Neptune are known to support Trojans, but Saturn and Uranus are also believed to share their orbits with similar populations of small bodies. Recent dynamical modeling suggests a genetic relationship among transneptunian objects (TNOs) and Jupiter and Neptune Trojans: All these bodies are believed to have formed at large heliocentric distances in a region rich in frozen volatiles. In this context, the analysis and the comparison of the physical properties of Trojans, Centaurs, and TNOs can help us to constrain the link among them and the scenario of the planetary formation in the outer solar system. This chapter presents an overview of current knowledge of the physical properties of Trojans. Since the Jupiter Trojans are the most well studied of the Trojan populations, discussion is centered on the analysis of the properties of this group and comparison with asteroids, comets, Centaurs, and TNOs. The physical characteristics of Jupiter Trojans share some similarities with those of the other populations of small bodies of the outer solar system, but also some notable differences. Some analogies with neutral/less-red Centaurs suggest that Jupiter Trojans are more similar to the active and post-active comets than to the non-active icy bodies. This may support a genetical link among these objects, but the complete puzzle is still far from being understood.

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