A defining characteristic of the planet Venus is its thick, CO₂-dominated atmosphere. Despite over 50 years of robotic exploration of Venus, including thirteen successful atmospheric probes and landers, our knowledge of N₂, the second most abundant compound in the atmosphere, is highly uncertain¹. We report the first measurement of the nitrogen content of Venus’s atmosphere at altitudes between 60 and 100 km. Our result, 5.0 ± 0.4 v% N₂, is 40% higher than the value of 3.5 v% N₂ reported for the lower atmosphere (<50 km altitude). Our discovery of altitude-dependent variations in the N₂ content of the atmosphere defies early expectations of homogeneous composition below 100 km (for example, see ref. ¹), and necessitates complete chemical modelling to investigate chemical versus physical explanations for the enhanced N₂ in the upper atmosphere. The existence of chemically distinct lower and upper atmosphere regions complicates the use of remote sensing measurements of the upper atmosphere to infer the properties of the lower atmosphere and surface, an important lesson that also extends to the growing field of exoplanet astronomy.

金星行星的主要特征是其浓厚的，以CO ₂为主的大气。尽管对金星进行了50多年的机器人探索，包括成功地进行了13次大气探测器和着陆器，但我们对N ₂的知识仍是高度不确定的，N ₂是大气中第二大化合物，这是非常不确定的¹。我们报告了首次测量60至100公里之间的金星大气中的氮含量。我们的结果为5.0±0.4 v％N ₂，比低层大气（<50 km高度）报道的3.5 v％N ₂的值高40％。我们发现N _2中与海拔有关的变化大气层的含量不能满足100 km以下均匀成分的早期期望（例如，参见参考资料¹），并且需要完整的化学模型来研究高空N ₂增强的化学和物理解释。化学上不同的下部和上部大气区的存在使对上部大气的遥感测量的使用复杂化，以推断下部大气和地表的特性，这一重要的教训也延伸到系外行星天文学的发展领域。