Hidden in a canyon on Mars, scientists have discovered a field of solid, windswept sand that turned into rock about a billion years ago.
Despite being heavily eroded, this icy paleodune plain has withstood time very well, far more so than the fossilized waves of sand on Earth, which are subject to the vagaries of wind, water and the changing landscapes of deep time.
Understanding how these duneforms have stood the test of time could give us an idea of the sedimentary processes on Mars and at the same time reveal something about the planet’s geological history.
“This level of conservation is rare for Earth’s sand dunes due to ongoing erosion and tectonics,” explains planetary scientist Matthew Chojnacki of the Planetary Science Institute.
“Based on the relationships of the dune deposit to other geological units and modern erosion rates, we estimate them to be around one billion years old.”
On Mars today, wind-raised sand dunes are a common feature, and the size and arrangement of those set in the widest part of the Valles Marineris canyon – the Melas Chasma – seem remarkably similar to those formed more recently.
This suggests that the climate and atmosphere on Mars have changed little in a very, very long time. Astronomers say the orientation, length, height, shape, and slope of the Melas Chasma paleo-dunes resemble newly formed sand waves seen elsewhere on the Red Planet.
“This indicates that the main wind directions responsible for the shape of the dunes have not changed substantially over time,” Chojnacki told EarthSky.
“We also see sand dunes of very similar size and spaced by the two time periods. This may indicate that the atmospheric pressure was not significantly different.”
Using images from the High Resolution Imaging Science Experiment (HiRISE) and data from Martian topography, the researchers documented and dated the shape properties of the Melas Chasma bed.
Although the topography of this canyon is still incomplete, as some of the dunes have been eroded or buried, the paleo-dunes we can decipher “do not paint a dramatically different picture from what can be obtained from their modern counterparts”, the researchers explain.
The authors found that some dunes were buried under tens of meters of material, which appeared to come from a catastrophic volcanic event.
Sometime later, the authors predict, a volatile compound made contact with the compacted sand dunes and helped harden them, freezing the waves over time as they migrated across the Melas Chasma.
This same type of process can be seen on Earth when groundwater invades a partially buried sand dune – formed layers of lithified sand like those famous striped structures seen in Zion National Park. Unlike our planet, however, the lithified sand dunes on Mars have far fewer elements to contend with.
In the absence of water, vegetation, or plate tectonics, exposure to trade winds is the main erode on Mars and, in deep time, this has helped chisel the volcanic shell that once covered these dunes.
The mere existence and degree of conservation observed in these dunes indicates an important difference in the evolution of the landscape of Earth and Mars.
While ancient lithified sand dunes on Earth are rare to find and much more eroded, Melas Chasma appears to possess “vast fields of paleo-dunes scattered across the basin floor, where many duneforms and their morphology appear largely intact.”
“Water and tectonics that constantly reshape the surface of the Earth are not currently a factor on Mars, so there is an opportunity to learn from the red planet’s geological data,” says Chojnacki.
“These results inform us that wind-driven sand transport, deposition and lithification have occurred throughout much of Mars’ recent history and illustrate how landscape evolution is remarkably different from that of Earth.”
The study was published in JGR planets.