Recent findings of NO near Gale Crater on Mars have been explained by two pathways: formation of nitric acid (HNO₃) in a warm climate or formation of peroxynitric acid (HO₂NO₂) in a cool climate. Here, we put forth two hitherto unexplored pathways: (a) deposition of nitric/peroxynitric acid onto ice particles in a cold atmosphere, which settle quickly onto Mars' surface and (b) solar energetic particle-induced production of nitric/peroxynitric acid. The deposition rates are enhanced and NO production is more efficient under the higher atmospheric pressures typical of Mars' ancient atmosphere. Depending on the unknown rate at which nitric/peroxynitric acid is lost from the surface, the new pathways could result in larger NO-levels than those detected by the Mars Science Laboratory. We predict a 2:1 ratio of nitrite:nitrate would have deposited in cool surface climates with an icy atmosphere, whereas orders of magnitude more nitrate than nitrite is expected from warm surface climates.

中文翻译：

---

冰冷大气中古火星的固氮


最近在火星盖尔陨石坑附近发现的一氧化氮可以用两种途径来解释：在温暖气候中形成硝酸 （HNO₃），或在凉爽气候中形成过氧硝酸 （HO₂NO₂）。在这里，我们提出了两种迄今未被探索的途径：（a） 硝酸/过氧硝酸在寒冷大气中沉积到冰颗粒上，这些冰颗粒迅速沉降到火星表面，以及 （b） 太阳能高能粒子诱导的硝酸/过氧硝酸的产生。沉积速率得到提高，在火星古老大气层典型的较高大气压下，NO 的产生效率更高。根据硝酸/过氧硝酸从表面流失的未知速率，新途径可能导致比火星科学实验室检测到的 NO 水平更大的 NO 水平。我们预测亚硝酸盐：硝酸盐的比例将沉积在具有冰冷大气层的凉爽地表气候中，而在温暖的地表气候中，预计硝酸盐比亚硝酸盐多几个数量级。