Titan, Saturn’s largest moon, has its atmosphere filled with a thick organic photochemical haze. These suspended solid nanoparticles are one of the most complex organic materials in the Solar System. In situ measurements from the successful Cassini space mission gave first clues on the aerosol's chemical composition: pyrolysis coupled to mass spectrometry revealed a nitrogen-rich core, whereas infrared measurements highlighted poly-aromatic-hydrocarbon (PAH) signatures. The combination of these observations supports a general model of nitrogenated-polycyclic aromatic hydrocarbon (N-PAH). To constrain the generic picture and understand the formation of such macromolecules in Titan’s atmosphere, we simulated the haze synthesis in the laboratory. Small (3–10 rings) N-PAH molecules composing the material were extracted, focusing on the prime aromatization and growth processes. By high-resolution atomic force microscopy (AFM), we imaged key chemical structures with atomic resolution. We resolved N-rich elongated molecules involving five-membered aromatic rings, consistent with a repetitive cata-condensation pattern via addition of C₃N units. These atomic-scale observations bridge the gap between gas phase atmospheric reactants and the macroscopic structure of Titan’s haze.

土星最大的卫星土卫六的大气层充满了厚厚的有机光化学薄雾。这些悬浮的固体纳米粒子是太阳系中最复杂的有机材料之一。成功的卡西尼号太空任务的原位测量提供了关于气溶胶化学成分的第一个线索：热解与质谱联用揭示了一个富含氮的核心，而红外测量则突出了多环芳烃 (PAH) 特征。这些观察结果的结合支持了含氮多环芳烃 (N-PAH) 的一般模型。为了限制通用图片并了解泰坦大气中此类大分子的形成，我们在实验室模拟了雾霾合成。提取了构成材料的小（3-10 个环）N-PAH 分子，专注于主要的芳构化和生长过程。通过高分辨率原子力显微镜 (AFM)，我们以原子分辨率对关键化学结构进行了成像。我们解析了涉及五元芳环的富含 N 的细长分子，与重复的通过添加 C ₃ N 单元的催化缩合模式。这些原子尺度的观测弥合了气相大气反应物与泰坦雾霾宏观结构之间的差距。