A little martian clay

Ken Tapping, April 10, 2013

In the sky this week…

  • Jupiter dominates the southwestern sky during the evening.
  • Saturn rises around 10 p.m.
  • The Moon will be New on the 10th.

Over the last few weeks, the rover Curiosity, which is currently exploring the surface of Mars, came up with another important discovery. On Earth the stuff it found is common and scarcely commented on. However, on Mars it tells us something very important. What Curiosity had discovered is clay.

Not that many years ago, astronomy books had images of Mars that were blurry, showing little more than a reddish disc with dark patches and polar caps which could have been ice. People were still arguing as to whether the “canals” mapped by Percival Lowell in the late 19th Century and early 20th were real. Moreover, it was widely accepted that the darkening wave seen moving down from the Martian poles in spring and summer was vegetation sprouting in response to moisture from the melting polar ice flowing towards the equator.

In 1964 the spacecraft Mariner 4 passed within 10,000 km of the Martian surface and sent back pictures that shattered those illusions. There were no canals, no patches of vegetation, just desert, rocks and craters. Mars looked more like the Moon than the Earth. All of a sudden our ideas of H.G. Wells’ Martians looking enviously at our world, the Martian princesses dreamt up by Edgar Rice Burroughs, or the enigmatic beings from the imagination of Ray Bradbury evaporated.

Or did they? More spacecraft flybys, mapping and surveying from orbiting spacecraft, and then the landers Vikings 1 and 2, Spirit and Opportunity and now Curiosity have changed our view again. Mars looks as though in its distant past it was a hospitable place for living things. However, now the Red Planet has become a frozen, almost airless, arid desert, descendants of those creatures could still be lurking below the surface of the ground.

From space we see canyons, dry riverbeds, deltas and places that could have been large lakes. Spirit, Opportunity and now Curiosity have found deposits formed by flowing water and just below the surface dust, ice. Then recently, Curiosity scratched the ground and found clay.

Clay is special stuff. It starts as fine rock flour where glacial ice or flowing water erodes rock down to fine dust. This material is easily carried by water and only starts to settle to the bottom in lakes or seas where the water sits still for a long time. We have excellent examples of this here in the Okanagan Valley, where glacial streams washed rock flour into a lake thousands of years ago. In the still water the rock flour settled to the bottom, forming thick layers of clay. When the lake drained down to the current levels, clay cliffs were left either side of the lake and are a major local feature today. Now we know something like this must have happened on Mars, billions of years ago. In our local clays we can even see the layers, deposited year by year. What will we see when have our first close look at those Martian clays?

Since the 1960’s, space missions have turned blurry discs into worlds, with geography, geology and maybe soon, biology. We also now see our Earth as one planet among many.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355

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