How Ash and Water Intricately Sculpted the Surface of Mars
The plateaus that flank the largest canyon in the Solar System are shrouded in hypnotically complex landforms called light-toned layered deposits. Fifteen years ago, PSI Senior Scientist Catherine Weitz first hypothesized that these unique landforms were layers of volcanic ash molded by water.
But, due to low imaging data coverage and a thick layer of Martian dust occulting these deposits from scientific eyes, their origins, history, and arrangement on the landscape remained mysterious.
A paper led by Ivan Mishev, a graduate student at York University working under the mentorship of his co-author and PSI Senior Scientist Isaac Smith, mapped these deposits in greater detail than ever before. They used data from instruments onboard NASA’s Mars Reconnaissance Orbiter – including the shallow radar sounder called SHARAD, the High Resolution Imaging Science Experiment, and the Context Camera – as well as the narrow-angle Mars Orbiter Camera onboard Mars Global Surveyor.
“Shallow radar worked well for this because in some places, these deposits are covered by dust,” Smith said. “Let’s say you have a rug, and under your rug there are some coins in some places and bare wood in others. You can’t tell where the coins are if you take a photograph. In this case, the rug is dust and the coins are huge, hundreds of kilometers squared, layered deposits. The magic of shallow radar is you don’t have to pull up the rug.”
They found that the deposits are more widespread than once thought and that there are three distinct deposit types that blend into each other, adding two types to the scientific literature.
“We interpret this to mean that it’s all from the same origin, but the ash fall was reworked to varying degrees,” Smith said.
Some places didn’t get reworked by water at all and likely just turned to rock. In other areas, it appears that rain fell, leeched through that ash and chemically altered it as it washed some minerals away and left others. The material that was washed away was deposited in layers, some more than 250 feet thick – about as tall as a giant sequoia.
Then they identified a layer deposit type in which water was present but for only a short amount of time. They dubbed these “weakly-layered deposits.”
“The nice part of the study is that we now have a much better picture of where water was available on Mars,” Smith said. “We see that the ash fall was much more widespread than previously thought, and one of the conclusions is that the water was within 65 miles of the canyon rim. Its proximity tells us that the canyon either was the source of water vapor that became local rainfall, or the canyon affected the weather patterns enough that the rain was only there.”
This work will also help inform scientific understanding of Mars’ evolution and sharpen computer models of the red planet.
Other PSI authors include Senior Scientists Matt Chojnacki and Nathan Putzig, PSI’s Associate Director.
PSI support for this work came from a NASA MDAP Grant (80NSS‐C17K0437), a Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN‐2019‐ 06351), and a Canadian Space Agency Research Opportunities in Space Science Grant (22EXPROSS3). Smith would also like to thank the Canadian Space Agency for funding Mishev’s portion of the work.
