Alfonso is satisfied with the scientific samples we have collected over the past two days and gives us the day off to search for drilling samples to ship home. Daniel and I walk back up to The Wall and inspect several salt boulders that have fallen from the exposed rock face above. We measure them to see if they will fit inside the coolers that will be used to ship them home to the US for drilling tests. We select one with clear, transparent faces and begin trimming it with the percussive hammer chisel to fit in the cooler. Alfonso helps us select a medium-sized polygon that has popped loose from the ground. We put both in the back of a pickup truck alongside the other gear that we are bringing back down to camp.
Next, we decide to test a custom 1” diameter auger with a full-faced bit to see how it will drill in a polygon. The auger is 143 cm long and the drilling goes very quickly. This auger has a deep flute and moves cuttings to the surface very efficiently. The drilling does not require much force beyond the weight of the drill and no jamming of the bit is evident. We drill the entire hole without pulling out to see if the bit will get stuck but it does not. One person can pull it out without assistance. Adapting some features of the auger to a refined coring bit could improve coring performance.
Although industrial coring equipment could certainly be used to collect high quality samples much more quickly and efficiently than our handheld equipment, the point here is not to depart too far from sampling techniques that could be used on Mars with present-day technology. The results of these field trials will help us learn how and where to look for biological markers on Mars, using satellite and aerial imagery combined with ground sampling and analysis aboard a robotic rover.
The Salar Grande dry lake bed is about 70m deep. To reach the oldest layers, we will dig into an outcrop in a quarry near camp. We will work near the bottom of a manmade feature known as The Wall, presumably exposed during the mining activity that occurred here. Carrying our equipment through the quarry is treacherous due to the uneven ground covered with salt nodules. The salt sounds thin in places and is streaked with colors reminiscent of alpine snowpack or ice on a glacier. Vultures eye us warily as we open up our cases and set up the generator. For today’s work, we will use a more powerful drill with an SDS-Max quick change tool interface and a chisel to dig down to unweathered salt at the base of The Wall.
Alfonso wants to remove about 12 inches of weathered overburden to get to the pristine beds below. This takes some muscle, because we must apply pressure to the chisel in a horizontal position in order for the percussive hammer to work properly. In addition, the chisel can plunge deep into a crack in the salt and get stuck. After working for about an hour, we begin to see large, clear halite crystals. The astrobiologists will look for tiny bubbles inside the salt, which may contain the remnants of ancient microbes. On this microscopic scale, the definition of life is somewhat more flexible than for macroorganisms, which can readily be identified as individuals. Since it is difficult, if not imposible, to track individual organisms at this scale as they rapidly multiply and mingle, the life span of these microbes can not be easily determined. What is known, however, is that the microbe colonies are very old because the crystals can be dated back to the age of the ancient lake (~2-5 million years).
As we chip around a large crystal of interest, Alfonso and Kim (SETI) sterilize their collection tools. The crystal is internally fractured and does not come out in one piece. Still, they collect the bits and place them in sterilized sample collection tubes. Then it is time to attempt collection of a core from the freshly exposed beds. The coring direction is horizontal, presenting a challenge for manual drilling because it is difficult to both support the drill and provide adequate force on the bit at the same time. The cuttings are pure white salt powder and we experience the same issues collecting cores as we did earlier in the nodules.