The Chemical and Mineralogy instrument, or CheMin for short, performs chemical analysis of powdered rock samples to identify the types and amounts of different minerals that are present.
|Main Job||To study the mineralogy and chemical composition of rocks and soil.|
|Location||Inside the Curiosity rover's body.|
|Size||About the size of a laptop computer inside a carrying case.|
|Spectrometer Type||An X-ray diffraction and fluorescence instrument.|
|Measurement||Takes up to 10 hours of analysis time, spread out over two or more Martian nights, although some samples may provide acceptable results in a single sol (Martian day).|
The Chemistry and Mineralogy instrument, or CheMin for short, identifies and measures the abundances of various minerals on Mars. Examples of minerals found on Mars so far are olivine, pyroxenes, hematite, magnetite, gypsum, and phyllosilicates.
Minerals are indicative of environmental conditions that existed when they formed. For example, olivine and pyroxene, two primary minerals in basalt, form when lava solidifies. Jarosite, found in sedimentary rocks by both the Curiosity and Opportunity rovers on Mars, precipitates out of water.
Using CheMin, scientists are able to study further the role that water, an essential ingredient for life as we know it, played in forming minerals on Mars. For example, gypsum is a mineral that contains calcium, sulfur, and water. Anhydrite is a calcium and sulfur mineral with no water in its crystal structure. CheMin is able to distinguish the two. Different minerals are linked to certain kinds of environments. Scientists use CheMin to search for mineral clues indicative of a past Martian environment that might have supported life.
To prepare rock samples for analysis, the rover drills into rocks, collects the resulting fine powder, and delivers it to a sample holder. It uses a scoop for collecting soil.
CheMin then directs a beam of X-rays as fine as a human hair through the powdered material. X-rays, like visible light, are a form of electromagnetic radiation. They have a much shorter wavelength that cannot be seen with the naked eye. When the X-ray beam interacts with the rock or soil sample, some of the X-rays are absorbed by atoms in the sample and re-emitted or fluoresced at energies that are characteristic of the particular atoms present.
In X-ray diffraction, some X-rays bounce away at the same angle from the internal crystal structure in the sample. When this happens, they mutually reinforce each other and produce a distinctive signal. Scientists can measure the angle at which X-rays are diffracted toward the detector and use that to identify minerals. For example, when a sample containing the mineral halite (common table salt, or NaCl), was placed in CheMin, the instrument produced a specific diffraction pattern that identified that mineral’s structure.
Because all minerals diffract X-rays in a characteristic pattern and all elements emit X-rays with a unique set of energy levels, scientists can use the information from X-ray diffraction to identify the crystalline structure of materials the rover encounters on Mars. A Charge-Coupled Device (CCD) collects both diffraction and fluorescence information.