More evidence for a very wet early Mars

Volcanic bomb sag found by the Spirit rover. Credit: NASA/JPL

The idea that Mars used to be a “water world” and sort of like a smaller version of Earth in many ways is now pretty much accepted among planetary scientists; the debate continues however as to just how wet it was and for how long. The answer would have direct implications for the possibility of life ever having started there.

Two more pieces of the puzzle now suggest, or reinforce the notion, that Mars was indeed a much wetter place than the cold, dry desert we see today.

First, new findings regarding a discovery made by the Spirit rover a few years ago indicate that water was much more abundant and the atmosphere was probably at least twenty times thicker than it is now, which would have allowed surface water to exist.

The evidence comes from a rock fragment found embedded in volcanic sediment, known on Earth as a bomb sag since the sediment visibly “sags” below the rock as a result of the rock penetrating the sediment from the impact (after being ejected during a volcanic eruption).

Josef Dufek, an Assistant Professor at Georgia Tech University, has been studying the Martian bomb sag to see what it can tell us about conditions on Mars millions or billions of years ago. His findings were just published in the journal Geophysical Research Letters.

He re-created the bomb sag’s characteristics in the laboratory, to determine the conditions present when it originally formed. Using dry, damp and saturated sand beds to replicate the sediments, he found that only the saturated sand beds produced similar results to what is seen on Mars, indicating that the Martian soil was likely very wet when the bomb sag formed.

“Our study is consistent with growing research that early Mars was at least a transiently watery world with a much denser atmosphere than we see today,” said Dufek. “We were only able to study one bomb sag at one location on the Red Planet. We hope to do future tests on other samples based on observations by the next rover, Curiosity.”

Elsewhere on Mars, the Mars Express orbiter has taken new images of ancient water-carved channels in the Acidalia Planitia region, a huge basin in the northern lowlands. Like others on the planet, they show “dendritic” drainage patterns, typically formed by runoff of water from rain or melting snow.

Dried-up channels in the Acidalia Planitia region of Mars, photographed by the Mars Express orbiter. Credit: ESA/DLR/FU Berlin (G. Neukum)

While there is still no consensus on how long the watery period lasted on Mars, to what extent or whether it was a warm or colder environment, it seems certain that water did play a large role in shaping the terrain of the Red Planet early in its history. But then Mars somehow lost most of its water, while Earth continued to maintain its rivers, lakes and oceans. How that change occurred can teach us more about how Mars evolved as well as our own planet’s geological and biological history.

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