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How Was Mars Made? | Formation of Mars

The planet Mars was formed, along with the rest of the solar system, about 4.6 billion years ago.  The leading theory is that the solar system began as a large, lumpy cloud of cold gas and dust, called the solar nebula. The nebula collapsed because of its own gravity and flattened into a spinning disk. Matter was drawn to the center of the disk, forming the sun.   

Artist's conception of our solar system's solar nebula, the cloud of gas and dust from which the planets formed.
Artist's conception of our solar system's solar nebula, the cloud of gas and dust from which the planets formed.
Credit: Painting copyright William K. Hartmann, Planetary Science Institute, Tucson

Other particles of matter stuck together to form clumps called planetesimals. Some of these combined to form asteroids, comets, moons and planets. The solar wind — charged particles streaming out from the sun — swept away the lighter elements, such as hydrogen and helium, leaving behind mostly small, rocky worlds. In the outer regions, however, gas giants made up of mostly hydrogen and helium formed because the solar wind was weaker.

This method of planet formation is called core accretion. The theory was first postulated in the late 18th century by Immanuel Kant and Pierre Laplace. Nebula theory helps explain how the planets in our solar system were formed. But with the discovery of "Super-Earth" planets orbiting other stars, a new theory, known as tidal downsizing was proposed.

Heating and cooling

Like all planets, Mars became hot as it formed because of the energy from these collisions. The planet's interior melted and denser elements such as iron sank to the center, forming the core. Lighter silicates formed the mantle, and the least-dense silicates formed the crust. Mars probably had a magnetic field for a few hundred million years, but as the planet cooled, the field died.

Mars Volcanoes Possibly Still Active, Pictures Show
The western scarp of Olympus Mons has both steep and gentle slopes with clear channels, some likely created by flowing liquid, perhaps water, and some apparently carved by glaciers.
Credit: Nature/ESA/G. Neukum

The young Mars had active volcanoes, which spewed lava across its surface, and water and carbon dioxide into the atmosphere. But there is no tectonic activity on Mars, so the volcanoes remained stationary and grew with each new eruption.

The volcanic activity also probably gave Mars a thicker atmosphere. Mars' magnetic field protected the planet from radiation and solar wind. With a higher atmospheric pressure, water probably flowed on Mars' surface, studies indicate. But about 3.5 billion years ago, Mars began to cool. Volcanoes erupted less and less and the magnetic field disappeared. The unprotected atmosphere was blown away by solar wind and the surface was bombarded by radiation.

Under these conditions, liquid water cannot exist on the surface. Studies suggest water is be trapped underground in both liquid and frozen forms and in the ice sheets of the polar ice caps.

All life as we know it requires liquid water, so there is much interest in finding evidence of it on Mars.

— Tim Sharp, Reference Editor

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Tim Sharp, Reference Editor

Tim Sharp

Tim writes and edits reference material for Space.com and other Purch websites. Previously, he was a Technology Editor at nytimes.com and the Online Editor at the Des Moines Register, where he led the newspaper's online news operation. He was also a copy editor at several newspapers. Before joining Purch, Tim was an editor at the Hazelden Foundation. He has a journalism degree from the University of Kansas. Follow Tim on .
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