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Ancient rivers show lack of plate tectonics on Mars and Titan

Unlike the topography of Earth, that of Mars and Titan was largely created by planet-wide processes such as thermal expansion, writes Andrew Masterson.

A radar image of Ligea Mare, a large hydrocarbon sea on Titan, and the rivers that drain into it.

River system patterns indicate that plate tectonics exerts a greater influence on landscape on Earth than it does on Mars or Saturn’s moon Titan.

The processes that created the topography of Titan and Mars are not well understood, so a team led by Benjamin Black from the City University of New York set out to see if ancient river networks visible on each might yield some clues.

In a study published in the journal Science, the team reports that drainage systems on Earth are influenced by a shorter “wavelength” of planetary activity than those of the other two bodies.

River systems – ancient or active – are informative when analysing topography, Black and colleagues explain, because their layout indicates whether they formed at the same time as the dominant topography, or later.

A process such as thermal expansion affects the entire surface area of a planet, or moon, and creates a topography known as a “long wavelength”. Black’s team found that the river systems visible on both Mars and Titan conformed to these long-wavelength patterns.

In the case of Mars, the team concluded, the river system were likely created before the later formation of valleys, and the craters created by the Noachian-Hesperian bombardment, a period of intense asteroid and meteorite impacts, around 4100 to 3700 million years ago.

The long-wavelength features on Titan, by contrast, are assumed to be comparatively recent, the result of moon-wide adjustments caused by shell-thickness variations arising from tidal heating or thermal expansion and contractions.

Earth, too, has river systems that in some cases follow long wavelength topography, but the direction and pattern is often disrupted and changed by more recent short-wavelength factors, such as mountain range formation and volcanic activity.

Black and colleagues suggest that the difference is because Earth has active plate tectonics, which frequently creates new short-wave structures, forcing river systems to recalibrate.

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Andrew Masterson is news editor of Cosmos.
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