The “Snow Line” on Venus’s Maxwell Montes: Varying Elevation Implies a Dynamic Atmosphere

Radar images of Venus’s tallest mountain range, Maxwell Montes, show a sharp increase in radar reflectivity, a “snow line,” at high elevation. This snow line has been inferred to represent a single common elevation (and thus temperature and pressure) above which metallic or semimetal compounds are present on the surface, either as direct precipitates from the atmosphere or from atmosphere–rock chemical reactions. Here, we show that Maxwell’s snow line is not at a constant elevation—it is ∼3.5 km higher in the NW than the SE. The best explanation is that atmospheric composition is not constant across Maxwell. The higher snow line elevation to the NW can be interpreted as a snow shadow, produced as winds from the SE cross Maxwell and becomes progressively depleted in its snow-producing component.