Atacama Field Test 2016: Day 4 (Oct 18) Drilling Sites 1 & 2

We wake up to a foggy morning. Moisture coats the ground and seeps into the surface salt, forming the characteristic smooth white salt nodules in which microbial life known as halophiles can exist. The astrobiologists point out the green and pink pigmentation both on the surface and inside these nodules which are an indication of possible biological activity. They explain that the pigmentation is a reaction to UV stress and protects the microorganisms from exposure to harmful levels of radiation. Due to the higher levels of UV radiation bombarding the surface of Mars, we would most likely have to drill several meters below the surface to detect any remnants of organic materials there. The moisture also plays a role in forming the polygons, which form when the clay from the old lake bed swells and shrinks according to its moisture content. The salt grows thick around the edges of the polygons, giving the landscape a very unusual beauty.

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A corner is selected for the 500m X 500m aerial survey and Jeff (UT Knoxville) sets up his drone operation base there. Inside the square, a smaller 4m X 4m sampling area is selected and marked off. Daniel and I begin practicing with our coring bits and augers near the sampling area. We will attempt to capture cores from a polygon (center and two edges) and a salt nodule. Pablo and Alfonso (SETI) begin using the Raman instrument to look for organic molecules on the surface of a promising nodule. After examining the nodule exterior, they use our Dremel as a Rock Abrasion Tool (RAT) to grind away the surface and expose layers beneath for examination.

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We select a polygon and begin drilling at the edge with a 23.9mm diameter auger. Hole starting is easy in the soft salt. We measure a surface hardness of ~20 MPa with a device called a Schmidt Hammer. Drilling proceeds quickly and brown and white powder (salt mixed with clay) starts piling up around the auger at the surface. After drilling down about 14cm, the powder turns white, indicating a layer of pure salt. We stop drilling and collect a sample in a sterilized tube. We continue the drilling operations down to the full auger depth of 60cm. At a depth somewhere below 23.5cm, the drill encounters a void and plunges down suddenly. The void defeats the sampling method, since the cuttings simply pile up underground. Drilling at the center of the polygon yields similar results.

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Collecting cores from the nodules turns out to be significantly more difficult. The nodules are more porous than the polygons and, therefore, softer. In fact, our Schmidt Hammer leaves a dent in the surface and registers no measurable rebound. The improvised coring bit that we are using does not move cuttings out of the hole quickly enough, jamming the core into the bit and complicating extraction. Nevertheless, we are able to generate useable cores. Alfonso uses sterilized tweezers to handle the cylindrical pieces and wraps them in aluminum foil for shipment to analysis labs back in the US.

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The team moves to a second drilling site in the afternoon. Cores are collected from a polygon and several nodules around the polygon. Longer cores can be collected from the polygons because they hold together better than the cores from the nodules.

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