Curiosity Finds Ancient Streambed But No Fish … Yet

A rock outcrop called Link pops out from beneath the ubiquitous red dust blanketing Mars’ surface. A fracture has exposed fresh gravels that scientists say could only have been created by flowing water. Credit: NASA/JPL-Caltech/MSSS

This looks so much like Earth. I see gravels like these in Duluth’s abundant creeks and rivers. Scientists are calling it the first evidence of streambed gravels on Mars. A fracture in an outcrop called “Link” shows rounded pieces of gravel eroding from a layer of white rock. Called a sedimentary conglomerate, the outcrop was formed by the deposition of water and is composed of many smaller rounded rocks cemented together. Water transport is the only process capable of making rounded gravels like these.

The name “Link” is derived from a rock formation in Canada’s Northwest Territories, where there’s also a lake with the same name. “Hottah”, named after another lake in the Northwest Territories, also bares similar sedimentary rocks.

Another exposed bedrock site named “Hottah” showing water-born gravels cemented into a rock layer. Where the rock erodes, pebbles fall to the ground. Click to see larger version. Credit: NASA/JPL-Caltech/MSSS

“The shapes tell you they were transported and the sizes tell you they couldn’t be transported by wind. They were transported by water flow,” said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Ariz.

OK, we all know by now that Mars once had flowing water, but there’s nothing like seeing the evidence come in piece by piece. We’re on a collective hunt that one day may take us to some steamy hot spring or even a river coursing through a deep underground cave.

“From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep,” said Curiosity science co-investigator William Dietrich of the University of California, Berkeley.

This image shows the topography around the area where rover landed back in August. The cross marks the actual landing spot. Higher elevations are colored in red; lower elevations in cooler colors. An alluvial fan, or fan-shaped deposit where debris spreads out downslope, is highlighted in lighter colors. On Earth, alluvial fans are often formed by water flowing downslope. Credit: NASA/JPL-Caltech/UofA

That sounds even more like a typical small stream or creek on Earth, making visualization of this ancient Martian waterway that much easier. The slabs of busted rock are tilted layers of ancient streambed that remind me a lot of a more recent concrete parking lot I watched an excavator dig up recently.

Left picture is a closeup of Mars gravel with a particularly round pebble highlighted. It’s just under 1/2 inch across. At right, rocks are rounded into pebbles by the action of water in Amity Creek in Duluth, Minn. Photo: Bob King

The rounded shapes indicate a lengthy transport from further up Gale Crater’s rim, most likely from where the larger channel called Peace Vallis (above) feeds into the alluvial fan. Curiosity is poised along the edge of that fan as it ambles toward Glenelg, an area where three terrains of scientific interest converge: light-colored bedrock, a region rich in small craters and pebbly ground similar to where Curiosity touched down. Read more details of the discovery HERE.

4 Responses

  1. Richard Keen

    Neat pictures, Bob. I just bought 3 cubic feet of 1/4-inch pebbles from a Colorado quarry to fill some weight bags for holding down a canopy tent. 3 cubic feet is about 150 pounds; a cubic yard is nearly a ton. They call is squeegee gravel, for some reason.
    If we ever put up canopy tents on Mars we’ll know where to go. Probably won’t need as much, since the Martian atmosphere is less that 1% of Earth’s and the winds have proportionally less force.
    Just another example of our ability to “live off the land” when we go to Mars.

  2. Sebastien

    Today I’m happy, because a month ago I said “I hope Curiosity finds peebles sometimes soon! This would be my proof for flowing water.”

    But is it really a proof? For all the other proofs so far, we’ve always found “non-flowing-water” equivalent explanations. Why would this time be different?

    1. astrobob

      From what I’ve read, this is a very good proof of flowing water. If the pebbles were very tiny, you could say that perhaps they were blown around by the wind, but mission scientists say these are too big and could only have been been created by flowing water.

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