Exploring the Planets

Forces from Within

Martian rocks carry the signature of an ancient magnetic field that has long since vanished. Interior forces buckled the surface into ridges, cliffs, and troughs. As Mars cooled, tectonic forces diminished, and today ground movement along faults and "Mars-quakes" are likely much less frequent.

The iron core of Mars cooled and solidified long ago. But early in its history, Mars did have a liquid core whose motion generated a magnetic field. Evidence of it was preserved in ancient molten rocks as they cooled. Traces are best preserved in the southern highlands. The absence of magnetic features in the large impact basins indicates that the magnetic field died out before they formed more than three billion years ago.

Mars Magnetic Features

Heat escaping from the planet's interior not only created melting of the crust and volcanism, but also produced tectonic forces that pulled and pushed the crust. The flanks of the Tharsis Rise contain vast volcanic plains that have been both pulled apart, to create narrow troughs called graben (right), and pushed together, to create long, narrow, twisting features called wrinkle ridges (left). Wrinkle ridges are common elsewhere on Mars and were in part created by global forces from the cooling and contraction of the planet's interior.

Tharsis Rise, Mars

Likely related to these same global contraction forces are thrust fault scarps. Thrust faults form scarps or cliffs where the crust is pushed together, breaks, and is forced upward. Amenthes Rupes (arrow) one of the largest thrust fault scarps, is over 400 kilometers (250 miles) long and up to 3 kilometers (2 miles) high.

Amenthes Rupes, Mars