VENUS: SIMILAR TO THE EARTH?
Since Venus is the terrestrial planet closest to the earth in size and mass, it is reasonable to expect that it will generally be the planet most like the earth. Of critical importance in developing a model for its interior is Venus's chemical composition: As we have seen, from estimates of what chemical elements were likely to have been present at the time of formation of the terrestrial planets and from observations of the planets' influences on the motion of spacecraft, astronomers have made estimates for the iron and nickel content in the terrestrial planets; as percentages of total mass, the iron and nickel content is as high as 65 percent for Mercury, up to 38 percent for Venus, up to 33 percent for the earth and the moon, and only up to 26 percent for Mars.
Such an iron content for Venus suggests that it ought to have a molten core (like that of the earth), occupying about the same fraction of Venus's interior as does the earth's (or significantly smaller than the core of Mercury). Overlying the molten iron-rich core is a silicate mantle and a crust on top of the mantle. It is possible that Venus (also like the earth) has an inner core of solid iron-rich material. Speculation for and against an inner core depends on estimates of the iron content of the planet.
