Evrim Yazgin
Cosmos science journalist
The search for water on other planets often starts when images reveal channels and canyons, or perhaps what look like seabeds on Earth.
But several different processes can lead to meandering channels appearing on the surface of Earth. They could be made by the bending of a river, lava melting through rock, or water cleaving through ice.
But not all these channels are made equal, according to descriptions in new research published in the journal Geology.
The researchers analysed thousands of bends in rivers and ice channels on Earth, as well as ice channels carved into the surface of the Moon.
The results could help explain the origins of formations seen on other planets and moons.
In rivers, for example, water goes faster around the outer edges of a bend. This is due to centrifugal forces – these are not real forces but are motions resulting from rotation. The outward motion you feel when going around a corner in a car is another example of a centrifugal force.
Water erodes the outer edge of a river bend and deposits sediments due to centrifugal forces.
This is different to thermal erosion such as in volcanic and ice channels where the bends are carved out through melting. These processes also don’t deposit sediment, meaning that the only changes in these channels are along the outer edge and the bends themselves are smaller.
Thermally eroded channels also have a greater number of accentuated bends downstream.
“This distinction sets up a great natural experiment for us to see if the shape, or size, of bends in rivers is distinct from those in volcanic or ice channels,” says co-author Tim Goudge, from the University of Texas (UT) in the US.
Initially, the team thought that it was an analysis error that led to the conclusion that river bends are comparatively larger than other channels.
“It wasn’t until the parameters for the code we had set for the volcanic channels on the Moon kept failing for the rivers on Earth that we realised, oh, that’s not a fault of the code – it’s an intrinsically different amplitude,” says co-author Juan Vasquez, also at UT.
On Earth, geologists can use several methods to determine what caused the carving of specific channels.
For one, the presence of running water is a sure sign that you’re looking at a river or stream. But in the absence of a fluid, other geological signs can be fingerprints to determining what kind of process led to the channel’s formation.
Such analysis is much harder to do on objects millions of kilometres away, such as Mars or Saturn’s moon Titan.
“There are these sinuous channels on the sides of Martian volcanoes,” Goudge says. “Some people have interpreted them as volcanic channels, and some people have interpreted them as rivers that formed when maybe snowpack on the top of the volcano melted.
“We’re saying that because volcanic channel bends are so distinct, you can measure those channels to find out.”
Goudge cautions against the research being used as a rule set in stone. Individual channels can vary dramatically, and a larger catalogue and further analysis is required for a diagnostic tool to be developed.
“But I think it has the potential to be if we understand it more,” he says.
