论文标题
密度，而不是半径，将岩石和水丰富的小行星隔开
Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
论文作者
论文摘要
小于海王星小的系外行星围绕红色矮星（M矮人）常见，而那些传播其宿主恒星的恒星构成了大部分已知温带世界，可用于大气表征。我们分析了M矮人周围所有已知的小型透明行星的质量和半径，并确定了三个种群：岩石，水丰富和气体富含气体。我们的结果与先前已知的双峰半径分布不一致，这是由于大气中的氢/氦络膜的损失而产生的。取而代之的是，我们提出，密度间隙将岩石与富含水的系外行星分开。包括轨道迁移的地层模型可以解释观察结果：雪线中形成岩石行星，而水丰富的世界在其外部形成，后来又向内迁移。
Exoplanets smaller than Neptune are common around red dwarf stars (M dwarfs), with those that transit their host star constituting the bulk of known temperate worlds amenable for atmospheric characterization. We analyze the masses and radii of all known small transiting planets around M dwarfs, identifying three populations: rocky, water-rich, and gas-rich. Our results are inconsistent with the previously known bimodal radius distribution arising from atmospheric loss of a hydrogen/helium envelope. Instead, we propose that a density gap separates rocky from water-rich exoplanets. Formation models that include orbital migration can explain the observations: Rocky planets form within the snow line, whereas water-rich worlds form outside it and later migrate inward.
