http://www.sci-news.com/space/map-early-mars-river-systems-09186.html
This image shows a suite of fluvial ridges on Mars (at –67.64 °E, 43.37 °S).
Image credit: J. Dickson.
Mars used to be a wet world, as evidenced by rock records of lakes, rivers, and glaciers.
The Martian river ridges were formed between 4 and 3 billion years ago (the Noachian to Hesperian period), when large rivers deposited sediments in their channels, rather than only having the water cut away at the surface.
Over time, sediment built up in the channels; once the water dried up, those ridges were all that was left of some rivers.
The ridges are present only in the southern hemisphere, where some of Mars’ oldest and most rugged terrain is, but this pattern is likely a preservation artifact.
“These ridges probably used to be all over the entire planet, but subsequent processes have buried them or eroded them away,” said lead author Dr. Jay Dickson, a researcher in the Division of Geological and Planetary Sciences at Caltech.
“The northern hemisphere is very smooth because it’s been resurfaced, primarily by lava flows.”
“Additionally, the southern highlands are some of the flattest surfaces in the Solar System,” said co-author Dr. Woodward Fischer, also from the Division of Geological and Planetary Sciences at Caltech.
“That exceptional flatness made for good sedimentary deposition, allowing the creation of the records being studied today.”
The new map allows planetary researchers to explore questions at global scales, rather than being limited to patchier, localized studies and extrapolating results to the whole hemisphere.
In addition to identifying 18 new fluvial ridges, using the map allowed the team to re-examine features that had previously been identified as fluvial ridges. Upon closer inspection, some weren’t formed by rivers after all, but rather lava flows or glaciers.
“If you only see a small part of a ridge, you might have an idea of how it formed,” Dr. Dickson said.
“But then you see it in a larger context — like, oh, it’s the flank of a volcano, it’s a lava flow.”
“So now we can more confidently determine which are fluvial ridges, versus ridges formed by other processes.”
“Now that we have a global understanding of the distribution of ancient rivers on Mars, future explorations — whether by rover or by astronauts — could use these rock records to investigate what past climates and tectonics were like.”
“One of the biggest breakthroughs in the last twenty years is the recognition that Mars has a sedimentary record, which means we’re not limited to studying the planet today,” Dr. Fischer said.
“We can ask questions about its history.”
“And in doing so, he says, we learn not only about a single planet’s past, but also find truths about how planets evolved… and why the Earth is habitable.”
The team’s results are published in the journal Geology.
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J.L. Dickson et al. The global distribution of depositional rivers on early Mars. Geology, published online December 21, 2020; doi: 10.1130/G48457.1
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