Trace element constraints on the hydro-geology of Gale Crater, Mars

The Curiosity Mars Rover landed in a region on Mars with plentifully evidence for ancient flowing water, including geologic remnants of lakes and rivers. This rover has an instrument called ‘ChemCam’ which fires a laser at rocks to vaporize a small amount of material and, from the light emitted by the vaporization, can determine the rock’s composition. While the instrument is theoretically capable of detecting most elements, the ability to detect certain trace elements has just been developed. Trace elements are chemicals present in rocks in very small amounts (less than 0.1 % and often much less than that). These elements behave in ways both similar and different than major elements, mainly because of differences in their mass and affinity for minerals. These different behaviors mean that trace elements and major elements will behave dissimilarly depending on environmental factors. By understanding the distribution of these trace elements, we can learn more about ancient environments on Mars. Elements on the periodic table are placed into ‘Groups’ which have similar chemical properties, so a trace element like lithium should behave like a major element in the same group, such as sodium. However, lithium is much lighter than sodium and is much easier to for the environment to move around. In this way and other similar ways, trace elements can be transported in the environment very differently than similar major elements; trace elements can also be deposited in different minerals than similar major elements. Minerals have strongly enforced, clear cut rules for their crystal structures and for an element to replace a different element in a spot in that structure, its shape and electrical charge must closely match the element being replaced. So, by learning how the trace elements changed during alteration of the original volcanic rocks and transportation of subsequent sediments, we can create new insights into the ancient Martian environment