Astronomical surveys have discovered thousands of transiting exoplanets, revealing that rocky planets are common in the galaxy. A planet's interior chemistry is frequently inferred by average density, described by mass-radius (M-R) relationships. However, M-R relationships give rise to non-unique interpretations of a planet's interior composition, an issue that limits our ability to characterize far-away worlds. We present experimental and density functional theoretical results addressing the influence of an ultra-reducing (oxygen-poor) interior chemistry on rocky mantle phases and discuss the possible implications for atmospheric observables. We show that silicon carbide (SiC) and molecular nitrogen (N₂) react to form solid silicon nitride (γ-Si₃N₄) at high pressures and high temperatures in a laser-heated diamond-anvil cell, consistent with ab initio computations. Si₃N₄ remains stable under extreme conditions and when quenched to ambient conditions. As SiC is a common compound found under very reducing conditions, these results indicate that nitrogen may form solid phases in an oxygen-poor rocky planet. If, by sequestering nitrogen in a planet's mantle, the distribution of nitrogen between a planet's interior and atmosphere is altered (i.e., a nitrogen-rich mantle and nitrogen-poor atmosphere), these results indicate that there may be atmospheric observables connected to the mantle-redox state of a rocky planet besides the oxygen-containing phases ubiquitous in exoplanet literature.

中文翻译：

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对还原行星岩石地幔中固态氮化物相的实验约束和对可观测大气成分的影响

天文调查发现了数千颗凌日系外行星，揭示了岩石行星在银河系中很常见。一颗行星的内部化学成分经常通过平均密度来推断，用质量半径 (MR) 关系来描述。然而，MR 关系会导致对行星内部成分的非独特解释，这个问题限制了我们描述遥远世界的能力。我们提出了实验和密度泛函理论结果，解决了超还原（贫氧）内部化学对岩石地幔相的影响，并讨论了对大气可观测性的可能影响。我们表明碳化硅 (SiC) 和分子氮 (N ₂ ) 反应形成固体氮化硅 (γ-Si ₃ N ₄) 在激光加热的金刚石砧室中的高压和高温下，与 ab initio 计算一致。Si ₃ N ₄在极端条件下和淬火至环境条件时保持稳定。由于 SiC 是一种在还原性极强的条件下发现的常见化合物，因此这些结果表明，氮可能会在缺氧的岩石行星中形成固相。如果通过在行星地幔中隔离氮，改变行星内部和大气之间的氮分布（即富含氮的地幔和贫氮的大气），这些结果表明可能存在与地幔相关的大气观测- 除了系外行星文献中普遍存在的含氧相之外，岩石行星的氧化还原状态。