The detection of molecules on the coldest and outermost objects in our Solar System has long been limited by the terrestrial atmosphere and sensitivity of the available instrumentation. However, near-infrared observations by the James Webb Space Telescope have provided an unprecedented view of the molecular diversity on the surfaces of trans-Neptunian objects (TNOs). Using the low spectral resolution PRISM mode on the near-infrared spectrograph as part of the Cycle 1 large programme, ‘Discovering the Surface Composition of trans-Neptunian objects’, we report the detection of several molecular ices throughout the TNO population, including H₂O, CO₂, ¹³CO₂, CO, CH₃OH and complex molecules and refractory materials containing aliphatic C–H, C≡N, O–H and N–H bonds. As a result of the imprint that these molecules leave on the spectra, three main compositional groups consistently emerge from multiple independent cluster analyses. Our results unlock the long-standing question of the interpretation of colour diversity, providing the much-needed compositional information. The marked separation of the three spectral clusters reveals sharp variations in the surface molecular constituents. The C/O and (CH + NH)/(C + O) ratios on the surface of TNOs are the primary indicators of the spectral differences among the three TNO compositional groups observed. We propose that these objects are fossil remnants of icy planetesimals, and that the three compositional groups provide a picture of the ice retention lines in the Solar System that likely occurred in the outer protoplanetary disk, possibly just before a major planetary migration.

长期以来，太阳系中最冷和最外层天体上的分子探测一直受到地球大气和可用仪器灵敏度的限制。然而，詹姆斯·韦伯太空望远镜的近红外观测为跨海王星天体 （TNO） 表面的分子多样性提供了前所未有的视图。作为第 1 周期大型计划“发现跨海王星天体的表面成分”的一部分，使用近红外光谱仪上的低光谱分辨率 PRISM 模式，我们报告了在整个 TNO 种群中检测到的几种分子冰，包括 H₂O、CO₂、¹³CO₂、CO、CH₃OH 以及含有脂肪族 C-H、C≡N、O-H 和 N-H 键的复杂分子和耐火材料。由于这些分子在光谱上留下的印记，三个主要组成组始终从多个独立的聚类分析中出现。我们的结果揭示了长期存在的色彩多样性解释问题，提供了急需的成分信息。三个光谱簇的显著分离揭示了表面分子成分的急剧变化。TNO 表面的 C/O 和 （CH + NH）/（C + O） 比率是观察到的三个 TNO 组成组之间光谱差异的主要指标。我们提出这些天体是冰冷小行星的化石残余物，并且这三个组成组提供了太阳系中冰保持线的图片，这些冰保持线可能发生在原行星外盘中，可能就在一次重大的行星迁移之前。