Terrestrial planets with large water inventories are likely ubiquitous and will be among the first Earth-sized planets to be characterized with upcoming telescopes. It has previously been argued that waterworlds—particularly those possessing more than 1% H₂O—experience limited melt production and outgassing due to the immense pressure overburden of their overlying oceans, unless subject to high internal heating. But an additional, underappreciated obstacle to outgassing on waterworlds is the high solubility of volatiles in high-pressure melts. Here, we investigate this phenomenon and show that volatile solubilities in melts probably prevent almost all magmatic outgassing from waterworlds. Specifically, for Earth-like gravity and oceanic crust composition, oceans or water ice exceeding 10–100 km in depth (0.1–1 GPa) preclude the exsolution of volatiles from partial melt of silicates. This solubility limit compounds the pressure overburden effect as large surface oceans limit both melt production and degassing from any partial melt that is produced. We apply these calculations to Trappist-1 planets to show that, given current mass and radius constraints and implied surface water inventories, Trappist-1f and -1g are unlikely to experience volcanic degassing. While other mechanisms for interior-surface volatile exchange are not completely excluded, the suppression of magmatic outgassing simplifies the range of possible atmospheric evolution trajectories and has implications for interpretation of ostensible biosignature gases, which we illustrate with a coupled model of planetary interior–climate–atmosphere evolution.

具有大量水库存的类地行星可能无处不在，并且将成为首批用即将到来的望远镜进行表征的地球大小的行星之一。以前有人认为水世界——尤其是那些拥有超过 1% H ₂O——由于其上覆海洋的巨大压力覆盖，经历了有限的熔体生产和除气，除非受到高内部加热。但是，在水世界中除气的另一个被低估的障碍是挥发物在高压熔体中的高溶解度。在这里，我们研究了这种现象，并表明熔体中的挥发性溶解度可能阻止了几乎所有来自水世界的岩浆释气。具体而言，对于类地重力和海洋地壳成分，深度超过 10-100 公里（0.1-1 GPa）的海洋或水冰阻止了部分熔融硅酸盐中挥发物的溶出。这种溶解度限制加剧了压力覆盖效应，因为大的表面海洋限制了熔体的产生和从产生的任何部分熔体中脱气。我们将这些计算应用于 Trappist-1 行星，以表明，鉴于当前的质量和半径限制以及隐含的地表水库存，Trappist-1f 和 -1g 不太可能经历火山脱气。虽然并没有完全排除内表面挥发物交换的其他机制，但对岩浆释气的抑制简化了可能的大气演化轨迹的范围，并对表面生物特征气体的解释产生了影响，我们用行星内部气候耦合模型来说明这一点。大气演化。