How Planetary Surfaces Are Formed

Earth is rich in planetary features liberally covered in mountains, valleys, lakes, oceans, volcanoes and the like. Not every planet is so varied however, and all that have been observed are lacking one of the biggest factors in a varied planetscape- life. But exactly how is the terrain that does exists—primarily mountains and craters—formed?

A Look at How Planetary Surfaces Are Formed

First when discussing planet surfaces it is assumed the discussion is about terrestrial planets- the rocky, solid planets most like Earth. The gas giants may have a "surface" of one type or another, such as the liquid water-ammonia ocean of Uranus, but primarily they are featureless levels of cloud and gas. For the rocky planets, however, one can study what is known as "planetary geology."

Planetary geology in astronomy actually covers more than planets, as it is the study of the solid surface and interior processes of any solid object in the solar system, which includes comets, asteroids, rings and satellites. Studying planetary surfaces is just one facet of planetary geology, but a very important one. By studying the surface and internal processes of planets, scientists can achieve a number of very important goals.

The Goals of Planetary Geology

There are three major goals in studying planetary geology; the first is the pure quest for knowledge. Astronomy can now examine the surfaces of far off planets, so why shouldn't we? Second, by studying the geology of planets and the like, we can better understand the process and life cycle of the universe around us. Finally, and most importantly, we can then use that information on the planets in something called "comparative planetology", wherein we compare one planet to another to learn even more. In comparing the evolution and processes and features of various heavenly bodies, astronomers have been able to conclude that there are three major factors that contribute not only to the formation of planetary surfaces but the changes that take place afterward.

How Planets Created

In brief, a planet is created when a star is formed, during the collapse of a nebula material collides and absorbs from a protoplanary disk, growing in size and composition until it is dense enough to generate its own gravity as a protoplanet. When it gets large enough it accumulates an extended atmosphere and becomes a planet. It is during this period of collision that some features, such as very large mountains or valleys, may be formed.

Collision On Planets And Geology

Depending on the thickness of the atmosphere on a planet it will be struck by other objects hurtling through space. The resultant "impact craters" can do a lot to shape the surface of the planet based on the size of the impact and the frequency.

Volcanism And Planets

Internal heating and gases push up on the mantle and crust of a planet, creating fissures or cones that can become volcanoes. Shifting geology often results from new volcanoes making direct changes by growing cones and indirect changes by covering nearby areas in magma and ash.

Final Thoughts

The variety in planetary geology—which might at first seem limited by the three factors that influence it—can be surprising. The surface of Venus, however, lacking the tectonic plates of Earth, does not seem to change much at all. Then, every 500 million years or so, internal pressure causes planet-wide upheaval, completely recycling the crust of the planet.