The origins of topography or surface elevations on Saturn's largest moon Titan may have more in common with the history of Martian landscapes than that of Earth, show an analysis of river maps of the three planetary bodies.
The environment on Titan may seem surprisingly familiar. Clouds condense and rain down on the surface, feeding rivers that flow into oceans and lakes.
Outside of Earth, Titan is the only other planetary body in the solar system with actively flowing rivers, though they are fed by liquid methane instead of water.
Long ago, Mars also hosted rivers, which scoured valleys across its now arid surface.
In a paper published in the journal Science, the researchers reported that Titan, like Mars but unlike Earth, has not undergone any active plate tectonics in its recent past.
The upheaval of mountains by plate tectonics deflects the paths that rivers take. The team found that this telltale signature was missing from river networks on Mars and Titan.
"While the processes that created Titan's topography are still enigmatic, this rules out some of the mechanisms we're most familiar with on Earth," said lead author Benjamin Black, Assistant Professor at the City College of New York.
Instead, Titan's topography may grow through processes like changes in the thickness of the moon's icy crust, due to tides from Saturn, the researchers said.
For the study, the team first compiled a map of river networks for Earth, Mars and Titan.
Such maps were previously made by others for Earth and Mars. The researchers generated a river map for Titan using images taken by NASA's Cassini spacecraft which has been circling Saturn and sending back to Earth stunning images of the planet's rings and moons since 2004.
For all three maps, the researchers marked the direction each river appeared to flow.
They then compared topographic maps for all three planetary bodies, at varying degrees of resolution.
The study also sheds some light on the evolution of the landscape on Mars, which once harboured a huge ocean and rivers of water.
The major features of Martian topography formed very early in the history of the planet, influencing the paths of younger river systems, even as volcanic eruptions and asteroid impacts scarred the planet's surface, the researchers said.
"It's remarkable that there are three worlds in the solar system where flowing rivers have carved into the landscape, either presently or in the past," said Taylor Perron, Associate Professor of Geology at Massachusetts Institute of Technology (MIT).
"There's this amazing opportunity to use the land forms the rivers have created to learn how the histories of these worlds are different," Perron said.