VENUS Structure | Surface | Atmosphere | Facts & Figures

The Interior of Venus

All four of the rocky planets, Mercury, Venus, Earth and Mars, are thought to be similar in structure. We are fairly certain that we know the interior structure of the Earth as we can make seismic measurements (using earthquakes for example), but as this is not yet practical on other planets we have to make estimates based on other data such as overall density.

Each planet has a core, mantle and crust, but the relative sizes vary considerably. As the density of each layer also varies, by measuring the overall density of the planet we can make a rough guess at the sizes of each layer by comparing them to the Earth. Mercury for example seems to have a relatively enormous core, while similar analysis of our own Moon implies that it's core is relatively small.

Theories of planetary formation suggest that initially the interiors of all of the rocky planets were fairly uniform. The phenomenon by which this uniform interior material separates out into core, mantle and crust according to density is known by planetary geologists as differentiation.

Venus has a core which is overall slightly larger than the Earth's. It is probably composed of a partially molten nickel/iron mixture with a molten inner core smaller than Earth's and a slightly cooler outer core which is larger.

Unlike the Earth, Venus does not have much in the way of a magnetic field. There are different theories to explain this observation which has been verified by many of the satellites which have orbited the planet in the last few decades. The core of Earth is slowly solidifying and it is this process which creates the dynamo that generates our magnetic field. One theory is that the core of Venus was prevented from starting to solidify for some reason, so there is no dynamo and hence no magnetic field. As the magnetic of the Earth protects us from much of the harmful solar wind, the lack of a magnetic field on Venus adds to the reasons why the surface is a very inhospitable place for humans!

Surrounding the core is a rocky mantle which is thought to be similar to that of the Earth, mainly made up of rocky "silcate" material.

The crust of Venus is also similar to the Earth's. The thickness of a planet's crust is determined by the rate at which the planet cooled after it's initial formation. As Venus and the Earth are so similar in size it is not suprising that both planets cooled at similar rates and so have crusts of similar thicknesses.

Once images of the surface were made with radar it became apparent that there were many features similar to those that geologists are used to studying on our own planet. This is not surprising considering just how similar in structure the two planets are. Also, despite having a mantle similar to the Earth, plate tectonics have not developed to the same extent on Venus as they have here. There are no "continents" as we would know them, although there are regions which are raised, and basins which are lower. See "The Surface" for more information.

Internet Links:
Planetary dynamos (NASA)
The magnetosphere of Venus (UCLA)
Planetary interiors (University of Oregon)