NASA / JPL-CALTECH / SCIENCE PHOTO LIBRARY NASA / JPL-CALTECH / SCIENCE PHOTO LIBRARY
Formation of a rocky planet, illustration. Starting from upper left, as a rocky planet forms the planet-forming material gathers in a process known as accretion. It grows larger in size, and increases in temperature, along with the pressure at its core (centre left). The energy from this initial planet forming process causes the planet's elements to heat up and melt (lower left). Upon melting, layers form and separate. The heavier elements sink to the bottom, the lighter ones float to the top. This material then separates into layers as it cools, which is known as differentiation. A fully formed planet slowly emerges, with an upper layer known as the crust, the mantle in the middle, and a solid iron core. This process will be studied on Mars by InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), which will help answer key questions about how rocky planets form.
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