Materials at high pressures and temperatures are of great interest for planetary science and astrophysics, warm dense-matter physics and inertial confinement fusion research. Planetary structure models rely on an understanding of the behaviour of elements and their mixtures under conditions that do not exist on Earth; at the same time, planets serve as natural laboratories for studying materials at extreme conditions. The topic of dense hydrogen is timely given the recent accurate measurements of the gravitational fields of Jupiter and Saturn, the current and upcoming progress in shock experiments, and the advances in numerical simulations of materials at high pressure. In this Review we discuss the connection between modelling planetary interiors and the high-pressure physics of hydrogen and helium. We summarize key experiments and theoretical approaches for determining the equation of state and phase diagram of hydrogen and helium. We relate this to current knowledge of the internal structures of Jupiter and Saturn, and discuss the importance of high-pressure physics to their characterization.

高压和高温下的材料对于行星科学和天体物理学，热密物质物理学和惯性约束聚变研究非常感兴趣。行星结构模型依赖于对元素及其混合物在地球上不存在的条件下的行为的理解。同时，行星充当了在极端条件下研究材料的自然实验室。鉴于最近对木星和土星重力场的精确测量，冲击实验的当前和即将进行的进展以及高压材料的数值模拟的进展，致密氢的话题是及时的。在这篇评论中，我们讨论了建模行星内部与氢和氦的高压物理学之间的联系。我们总结了确定氢和氦的状态方程和相图的关键实验和理论方法。我们将此与当前对木星和土星内部结构的了解联系起来，并讨论了高压物理学对其表征的重要性。