Venus’ radar-bright highlands: Different signatures and materials on Ovda Regio and on Maxwell Montes

•An enduring puzzle about Venus is why its highlands are bright in reflected radar (i.e., have surfaces of high apparent permittivity).•On equatorial highlands, the pattern or radar reflectance is consistent with the presence of a ferro-electric substance, confirming earlier work.•The ferroelectric substance on the equatorial highlands is likely chlorapatite, formed by reaction between igneous fluorapatite and HCl in the Venus atmosphere.•On the highlands of Maxwell Montes, the pattern of radar reflectance is consistent with presence of a semiconductor substance formed in chemical reaction between the atmosphere and the surface, not a ferro-electric like chlorapatite.•The radar difference between the equatorial highlands and Maxwell Montes apparently represents significant differences either in bedrock type or in atmosphere composition & temperature.