The science that describes the properties of droplets, bubbles and liquid films — namely capillarity, pioneered by Pierre-Simon Laplace at the start of the nineteenth century — therefore has relevance beyond our planet. Some of the implications for extraterrestrial environments are explored by Cordier and colleagues¹.

At the heart of capillarity is the notion of interfacial tension: in essence, the excess free energy of a liquid surface in contact with a vapour or a solid. The balance of interfacial energies is what determines how high a liquid column rises in a narrow capillary or pore, and to what extent a droplet sitting on a solid substrate will spread or contract into a bead (its wetting behaviour). Surface tension can hold small particles in place at a liquid surface even if the particles have a greater density than the liquid — witness iron filings floating on water. This process is favoured for substances with which water has a large contact angle, making the surface of a liquid ocean like that beneath the icy shell of Enceladus a likely place for hydrophobic organic particles to gather — as proposed recently following the observation of organic macromolecules in the icy plumes ejected through the crust². Flotation could also supply a means for organics to become concentrated, with prebiotic implications.

因此，描述液滴、气泡和液膜特性的科学（即毛细管现象，由皮埃尔-西蒙·拉普拉斯在 19 世纪初首创）具有超越我们星球的相关性。 Cordier 及其同事 ¹ 探讨了对地外环境的一些影响。

毛细现象的核心是界面张力的概念：本质上是液体表面与蒸气或固体接触的多余自由能。界面能量的平衡决定了液柱在狭窄的毛细管或孔隙中上升的高度，以及位于固体基质上的液滴在多大程度上扩散或收缩成珠子（其润湿行为）。即使颗粒的密度比液体的密度大，表面张力也可以将小颗粒固定在液体表面——铁屑漂浮在水面上就是见证。这一过程有利于与水有较大接触角的物质，使得像土卫二冰壳下的液体海洋表面成为疏水性有机颗粒聚集的可能场所——正如最近在观察有机大分子之后提出的那样。穿过地壳喷出的冰冷羽流 ² 。浮选还可以提供一种浓缩有机物的方法，具有益生元的意义。