Mars had water for longer than previously thought

High concentrations of silica point to the existence of groundwater long after lakes evaporated. This finding extends the potential window for life on the planet.

The discovery of light-toned bedrock – called ‘halos’ – with high concentrations of silica in Mars’ Gale crater, reveals that groundwater persisted once the lake in Gale crater dried up. The discovery was made by NASA’s Curiosity rover which traveled more than 16 km over 1,700 Martian days from the bottom of Gale crater to Mount Sharp in the crater’s center. For researchers who published the study in the journal Geophysical Research Letters, it is now a question of whether this extended window of water on Mars enabled life to develop.

We spoke to the lead author Jens Frydenvang about the work.

ResearchGate: What motivated this study?

Jens Frydenvang: The NASA Curiosity rover landed in Gale crater, Mars in 2012, and has been exploring the crater ever since. Already, this exploration has led to evidence of a long-lived lake (or lakes) early in Mars’ history; but we are still looking for evidence on how long this habitable environment persisted, and how Mars became the arid planet we know today. The results presented in this study, represent the strength of an exploratory rover like Curiosity, in that we were able to react to the unexpected findings of high-silica fracture-associated halos, and use the time needed to measure and understand them.

RG: Can you tell us what you found?

Frydenvang: We have found light toned areas – called halos – surrounding fractures in bedrock originating from deposits in the ancient Gale crater lake, and also in overlying bedrock originating from sand-dunes that were deposited after the lake had disappeared. These halos comprise very high silica concentration near the center-lines, that are interpreted to have been deposited from groundwater flowing through the fractures. As the halos are also found in the lithified sand-dunes, this points to substantial amounts of groundwater being present in Gale crater long after the lake eventually disappeared.

This is a mosaic of images from the navigation cameras on the NASA Curiosity rover shows 'halos' of lighter-toned bedrock around fractures. These halos comprise high concentrations of silica and indicate that liquid groundwater flowed through the rocks in Gale crater longer than previously believed. Credit: NASA/JPL-Caltech.

RG: How did you discover this?

Frydenvang: This discovery represents the ability of a capable rover like Curiosity, to discover and react to unexpected features. The first high-silica measurement was made using the ChemCam (Chemistry and Camera) instrument that I’m working on, and the halos themselves are visible in the images we got down from the rover cameras as light toned areas around fractures. Most of the science instruments on the Curiosity rover were utilized to measure and understand the nature of the halos.

RG: When did Mars have water? And when/how did it disappear?

Frydenvang: We believe that Gale crater held a lake 3.8-3.3 billion years ago, and that it might have lasted millions of years. What we show here, is that even long after the lake disappeared, substantial amounts of groundwater were present and flowed through the rocks in Gale crater. It is unfortunately not possible for us to date when this happened better. As for how liquid water disappeared from Mars, this is very much part of our ongoing research using the Curiosity rover and continuing our ascent of Mount Sharp in the center of Gale crater, but also using the NASA Maven spacecraft orbiting Mars.

RG: Why is this only being discovered now?

Frydenvang: The halos we’ve discovered are not visible to the spacecrafts orbiting Mars, and have only been observed over 20-30 m of elevation. Hence, we wouldn’t have found these without the Curiosity rover on the surface.

RG: What does it mean for our understanding of Mars? And its potential for life?

Frydenvang: Data from the Curiosity rover have already shown that Gale crater was once habitable. The big questions for us now, is for how long this environment persisted, and of course whether that window allowed for life to arise. This study shows that liquid water was present in the sub-surface of Gale crater for much longer than previously thought, which expands the window in which life could potentially have evolved on Mars.

Featured image courtesy of ESA/DLR/FU Berlin.