The Jupiter Trojans, being trapped around the stable L4 and L5 Jupiter Lagrangian points, are thought to be more primitive than the Main Belt asteroids. They are believed to have originated from a range of heliocentric distances in the trans-Neptunian region, to have subsequently been scattered inwards, and finally captured in their current location during the phase of Giant Planet migration. As a consequence, their bulk composition is expected to reflect that of the protoplanetary disk at the time and location of their formation. The photometric properties of Trojans appear to have a bi-modal distribution. A few Trojans have been discovered to be binary systems, suspected contact binaries, or to possess moonlets, which has revealed consistently low bulk densities (around \(1\times 10^{3}\) kg \(\mathrm {m}^{-3}\)) for those systems. Those estimates, together with the presence of a spin barrier between 4 and 4.8 h rotation period, suggest that low densities are a general property of the population, similar to that of cometary nuclei.

Current Trojan physical properties provide clues that relate to their formation that can, in turn, be traced back to the origin of the solar system. We review here our current knowledge on the physical properties of Trojans and the methods used for their determinations. Most of these methods are based on Earth-bound observations, and are limited by the large distance to these objects. The next breakthrough will be made possible by the Lucy mission, which, by visiting several Trojans during a tour through both clouds, will address many open questions and probably raise new ones. The combination of the ground truth for select objects provided by Lucy with the context view given by the Earth-bound observations will result in powerful synergy.

木星特洛伊小行星被困在稳定的 L4 和 L5 木星拉格朗日点周围，被认为比主带小行星更原始。据信它们起源于跨海王星区域的一系列日心距离，随后向内分散，并最终在巨行星迁移阶段被捕获在当前位置。因此，它们的整体成分预计将反映原行星盘在其形成时间和位置的成分。特洛伊木马的光度特性似乎具有双峰分布。一些特洛伊木马被发现是双星系统，疑似接触双星，或者拥有小卫星，这表明其体积密度始终较低（大约\(1\times 10^{3}\) kg \(\mathrm {m}^ {-3}\) ) 对于这些系统。这些估计，加上 4 至 4.8 小时自转周期之间存在的自旋势垒，表明低密度是群体的一般特性，类似于彗星核。

目前特洛伊的物理特性提供了与其形成相关的线索，而这些线索又可以追溯到太阳系的起源。我们在这里回顾一下我们目前对特洛伊木马的物理特性及其确定方法的了解。这些方法大多数都是基于地球观测，并且受到与这些物体距离较远的限制。下一个突破将由露西任务实现，该任务通过在两个云层中访问多个特洛伊木马，将解决许多悬而未决的问题，并可能提出新的问题。露西提供的选定物体的地面实况与地球观测给出的背景视图的结合将产生强大的协同作用。