One of the more distinctive things about Earth among the planets is that we have plate tectonics. In other words, the hard, outer shell of the planet (called the lithosphere) is divided into several cool, rigid plates that float atop a hotter, more fluid layer of rock (the asthenosphere). These rigid surface plates do not float placidly: their grinding, colliding, shifting, and diving causes earthquakes, fuels volcanoes, builds mountains, tears open oceans, and constantly remodels and resurfaces the planet.

That is a far cry from what is happening on Mars and Titan, according to a recent study published in Science. Researchers came to that conclusion by carefully analyzing the way rivers cut through each of these planetary bodies. On Earth, countless rivers and streams snake their way across the surface. On Mars, rivers dried up long ago, but evidence of their presence remains etched into the arid surface. On Titan, Saturn’s largest moon, rivers of liquid ethane and methane still flow into lakes.

By comparing imagery and data from all three planetary bodies, researchers noticed distinctive bends in the courses of rivers on Earth; these were formed as rivers were forced to wind around mountain ranges. These bends were absent in river networks on Mars and Titan. In an MIT press release, Benjamin Black, a geologist at the City College of New York, explained:

“Titan might have broad-scale highs and lows, which might have formed some time ago, and the rivers have been eroding into that topography ever since, as opposed to having new mountain ranges popping up all the time, with rivers constantly fighting against them.”

Read more about the study from New Scientist, Space.com, and the American Association for the Advancement of Science. Read the full study in Science. Read this NASA Earth Observatory story to learn more about how scientists are using satellites to study river width on Earth.

In the triptych at the top of the page, the image of Parana Valles on Mars was acquired by the Viking 1 orbiter on September 13, 1976. The image of the Nile was captured by NASA’s Terra satellite on August 10, 2000. NASA’s Cassini spacecraft captured the image of Vid Flumina on Titan on September 26, 2012.

Tags: Earth, geology, Mars, plate tectonics, rivers, Titan