Using contextual camera data from NASA’s Mars Reconnaissance Orbiter, planetary researchers generated an 8-billion-pixel global map of Mars and performed the first systematic global study of Martian fluvial (river) reefs.
Mars used to be a wet world, as evidenced by the stone records of lakes, rivers and glaciers.
Martian reefs formed between 4 and 3 billion years ago (the Noachian to Hesperian period), when large rivers deposited sediments in their channels, instead of just cutting off water at the surface.
Over time, sediment accumulated in the canals; when the water dried up, those reefs were all that was left of some rivers.
Reefs are present only in the southern hemisphere, where some of the oldest and harshest terrains of Mars are, but this pattern is probably an artifact for preservation.
“These ridges used to be all over the planet, but later processes buried or eroded them,” said lead author Dr. Jay Dickson, a researcher in the Department of Geological and Planetary Sciences at Caltech.
“The northern hemisphere is very smooth because it has been rebuilt, primarily by lava flows.”
“In addition, the southern mountains are some of the flattest surfaces of the solar system,” said co-author Dr. Woodward Fischer, also from the Department of Geological and Planetary Sciences at Caltech.
“That remarkable plane created good sedimentary deposition, allowing the creation of records that are being studied today.”
The new map allows planetary researchers to explore issues on a global scale, rather than being limited to patchwork, localized research, and extrapolating results to the entire hemisphere.
In addition to identifying 18 new fluvial reefs, the use of the map allowed the team to reconsider features that had previously been identified as fluvial reefs. Upon closer inspection, however, some did not form rivers, but lava flows or glaciers.
“If you see only a small part of the ridge, you may have an idea of how it came to be,” said Dr. Dickson.
“But then you see it in a broader context – like, oh, it’s the side of a volcano, it’s a lava flow.”
“So now we can determine with more confidence what the fluvial ridges are, compared to the ridges formed by other processes.”
“Now that we understand the distribution of ancient rivers on Mars globally, future research – whether by rover or astronaut – could use this rock data to investigate what the climate and tectonics were like.”
“One of the greatest achievements in the last twenty years is the recognition that Mars has sedimentary records, which means that today we are not limited to studying the planet,” said Dr. Fischer.
“We can ask questions about his history.”
“In doing so, he says, we learn not only about the past of a planet, but we also find truths about how the planets evolved … and why the Earth is habitable.”
The team’s results were published in the journal Geology.
JL Dickson and others. Global distribution of sedimentary rivers on early Mars. Geology, published online on December 21, 2020; doi: 10.1130 / G48457.1