Early Mars was covered in ice sheets, not flowing rivers

Anna Grau Galofre/Arizona State University

Image captured by helicopter over the western edge of the Devon ice cap, on western Devon Island in Nunavut. These ice channels, as well as the thermal state of its ice cap, inspired the idea that some Martian valleys didn't originate as rivers but as subglacial channels.

A large number of the valley networks scarring Mars’ surface were carved by water melting beneath glacial ice, not by free-flowing rivers as previously thought, according to a new study by Western and University of British Columbia researchers.

The findings effectively throw cold water on the dominant ‘warm and wet ancient Mars’ hypothesis, which proposes that rivers, rainfall and oceans once existed on the red planet.

The similarity between many Martian valleys and subglacial channels on Devon Island in the Canadian Arctic is striking and motivated this comparative study, published today in the journal Nature Geoscience.

Gordon Osinski, director of Western’s Institute for Earth and Space Exploration, has led conducted analogue work in the Canadian Arctic for years and studying valley formation on Earth is fundamental to understanding Mars’ surface as NASA prepares for human spaceflight to the red planet.

“Devon Island is one of the best analogues we have for Mars here on Earth,” said Osinski, a co-author on the study. “It is a cold, dry polar desert and we know the glaciation is largely cold-based.”

For the study, lead author Anna Grau Galofre, a former PhD student in UBC’s Department of Earth, Ocean and Atmospheric Sciences, developed and used new techniques to examine thousands of Martian valleys.

She and her co-authors, including Osinski, also compared the Martian valleys to the subglacial channels in the Canadian Arctic during three Western-led analogue space missions.

“For the last 40 years, since Mars’s valleys were first discovered, the assumption was that rivers once flowed on Mars, eroding and forming all of these valleys,” said Grau Galofre.

“But there are hundreds of valleys on Mars and they look very different from each other. If you look at Earth from a satellite you see a lot of valleys: some of them made by rivers, some made by glaciers, some made by other processes, and each type has a distinctive shape. Mars is similar, in that valleys look very different from each other, suggesting that many processes were at play to carve them.”

In total, the researchers analyzed more than 10,000 Martian valleys using a novel algorithm to infer their underlying erosion processes.

“Our study challenges the widely held view that most valley networks on Mars were formed by rivers fed by precipitation. While we found evidence consistent with a small handful of valley networks having formed in this way, our observations suggest that the majority formed beneath ice sheets.” Gordon Osinski, Western University

Grau Galofre’s theory also helps explain how the valleys would have formed 3.8 billion years ago on a planet that is farther away from the sun than Earth is, during a time when the sun was less intense.

“Climate modelling predicts that Mars’ ancient climate was much cooler during the time of valley network formation,” said Grau Galofre, currently a School of Earth and Space Exploration (SESE) Postdoctoral Fellow at Arizona State University.

For those thinking this is bad news for potentially finding life on Mars, think again.

A sheet of ice would lend more protection and stability of underlying water, as well as providing shelter from solar radiation in the absence of a magnetic field – something Mars once had, but which disappeared billions of years ago.

Composite image by Anna GrauA collage image showing Martian valleys (in grey, at top of image) superimposed with channels on Devon Island (in tan, at bottom). The shape of the channels as well as the overall network is almost identical. The top Mars portion of the image is a Context Camera (CTX ) mosaic, and the bottom portion is obtained from MAXAR/Esri through ArcGIS World Imagery.