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Planets, like people, grow and change over time: Evolving Worlds


Mars Sunset
This lovely, otherworldly evening was captured by the rover Spirit in 2005 as it peered toward the western sky from its perch in Gusev Crater on Mars. Image Credit: NASA/JPL/Texas A&M/Cornell

Like people, planets grow old. They start out full of energy, but over billions of years, they change. Instead of losing their hair, planets can lose their atmospheres and oceans. Instead of wrinkles, they may gather craters. And rather than becoming frail, planets cool and shrink, becoming more dense as they move into their senior years.

Earth's early atmosphere formed from
gases spewed by volcanic eruptions!
They continue to contribute to Earth's
atmosphere today. Much of the gas is
carbon dioxide and water vapor. Later
biological activity from early life added
oxygen to our atmosphere.
Earth's Early Atmosphere

Mars is an example of a planet past its youth. Planetary scientists envision a warmer, wetter early Mars, with flowing rivers and ocean and a thicker atmosphere, all surrounded by a protective global magnetic field. As Mars cooled, its core could no longer generate a magnetic field. Its interior became too cool to produce the volcanic eruptions that built and maintained the atmosphere. Without the protective shield of the magnetic field, the solar wind gradually eroded away Mars' diminished atmosphere. Water, once flowing across the surface, evaporated or became trapped in the subsurface or polar ice caps. Exploring how worlds evolve will help us understand more about Earth's own future -- and help us in our search for habitable planets!

Join us in this YSS topic as we investigate how planets evolve!

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Last Updated: 12 Sep 2014