When NASA’s Magellan probe circled Venus from 1990 to 1994, its radar imager found the planet’s mountains strangely bright, suggesting they may be covered with a radar-reflecting metal like tellurium. Now planetary scientists Bruce Fegley and Laura Schaefer of Washington University in St. Louis calculate that the high-altitude regions of Venus are actually frosted with a simple lead compound, lead sulfide. The researchers determined that only lead sulfide has the chemical and thermodynamic properties to match the features uncovered in the Magellan mission.

The metallic frost probably forms when metal-bearing gas spews out of Venusian volcanoes, rises up to higher, cooler altitudes, and condenses on the surface in a thin layer. Venus’s lead sulfide coating could yield important information during future space probes, Fegley says. By examining the ratios of various lead isotopes, planetary scientists could determine the age and geologic history of Venus’s surface.