Lesson Plan: BackgroundFrom the MER web site:
Many of the minerals that formed rocks on Mars contain iron, and the soil is iron-rich. The Mössbauer spectrometer is an instrument that was specially designed to study iron-bearing minerals. Because this science instrument is so specialized, it can determine the composition and abundance of these minerals to a high level of accuracy. This ability can also help us understand the magnetic properties of surface materials. The Mössbauer Spectrometer sensor head is small enough to fit in the palm of your hand. It is one of four instruments mounted on the turret at the end of the rover arm. Its electronics are housed inside the body of the rover (in the Warm Electronics Box, or WEB). Measurements are taken by placing the instrument's sensor head directly against a rock or soil sample. One Mössbauer measurement takes about 12 hours. The Mössbauer measurements are especially important because they will tell us something about which minerals are present in the rocks on Mars. Our ideas for martian mineralogy are based upon two types of data: spectroscopy from satellites, and Earth-based studied of martian meteorites. Click here for a list of minerals predicted by scientists to be present. Minerals are formed in all types of geological environments (except those in which it is too hot for solids to exist!). In many cases, a given mineral is diagnostic of some particular set of formation conditions. Scientists are hopeful that the Mössbauer spectrometers on the MERs and Beagle 2 will help identify which minerals are present. This is not an easy job, because the minerals that make up the rocks on Mars may be very tiny. A good analogy for this idea is a fruit salad... Imagine that you go to a restaurant and notice that there are two types of fruit salad on the menu: New England fruit salad and Hawaiian fruit salad. You ask the waitress what these are like, and she points to two large bowls on the other side of the room. From where you are sitting, both rocks (oops, I mean salads) look identical. But it's important to you to know which salad is which -- you want to know what's in them, and where the ingredients came from! So you get out of your chair and go over to take a look: now you can see that the New England fruit salad is made up of apples, pears, and peaches, while the Hawaiian salad has pineapples, papayas, and mangos. Now you can decide which one you want based on your knowledge of the ingredients. To a geologist, a rock is like a fruit salad... we need to know which minerals make up the rock in order to understand how it formed. Sometimes we can't identify the minerals unless we are very close up. Sometimes some of the ingredients (minerals) look alike (say, apples and pears), and we have to resort to more complicated testing to understand what is present. That's why we need a Mössbauer spectrometer on Mars -- to help us figure out what minerals are there... One last complication: to a geologist, even the sizes and relative amounts of minerals that are present may give us information on how a rock is formed. Most rocks are classified based on the size of the grains and their mineralogy (for an example, click here). All this information gives us an idea of how the rocks formed, and in what kind of environment.
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