Maxwell Montes, the tallest mountain range on Venus, rising to about 11 km (7 miles) above the planet’s mean radius. It forms part of the continent-sized upland called Ishtar Terra and lies just to the east of Ishtar’s high plateau, Lakshmi Planum. First observed as a bright feature in Earth-based radar observations of the planet made in the 1960s, the region initially was dubbed Maxwell after the British physicist James Clerk Maxwell, whose formulation of the laws that relate electricity and magnetism is the basis of radar (see Maxwell’s equations). Subsequent Earth-based and spacecraft radar observations revealed its mountainous nature.
Maxwell Montes is composed of a complex pattern of roughly parallel ridges with typical spacings of 3–10 km (2–6 miles). The ridges are thought to have formed as a result of intense tectonic deformation that probably involved both folding and faulting of the Venusian lithosphere. A major feature of Maxwell Montes is Cleopatra, a circular depression near its eastern margin that has a diameter of slightly more than 100 km (60 miles) and a depth of more than 2.5 km (1.6 miles). Suspected after its discovery of being a volcanic caldera, Cleopatra was later generally recognized to be an impact crater.
In radar images Maxwell Montes is one of the brightest features on Venus. This high radar reflectivity, responsible for the region’s early discovery, is due in part to its very rugged nature. It apparently is also due to the highest elevations on Venus being coated with some as-yet-unidentified material, perhaps an iron-containing mineral such as pyrite or magnetite, that is unusually reflective at radar wavelengths.