MIDAS and its first dust grain

This blog post is contributed by Mark Bentley, MIDAS Principal Investigator at the Space Research Institute (IWF) in Graz, Austria. One of the big challenges in planning MIDAS operations is predicting the amount of dust that we collect during an exposure. Measuring the rate of dust grains flying past Rosetta and their size distribution is, of course, part of our science, but to plan our operations, we need to have some idea of what to expect beforehand! This is particularly complicated because with MIDAS, we are interested in measuring the smallest cometary dust particles, less than 1 µm (micrometre or millionth of a metre) in size, and ground-based telescope observations that are used to study dust remotely are almost blind to these sizes. So with that in mind, we started our first exposure in mid-September, opening the shutter for about 4 days. MIDAS works by collecting dust grains on sticky targets that are then scanned at very high resolution using an atomic force microscope. Initial calculations suggested that we might find one particle of around 1 µm in an 80x80 µm scan. The “before” and “after” images are shown in the panel below - as you can see, nothing jumps out, as most of the features seen in the after image were also there before we opened the shutter, meaning that they are background contamination (this is why we need to take a scan before!). If you look closely, you might even convince yourself that one or more particles have disappeared, but this is just a result of small offsets in the position of each pixel. During the following weeks, the same target was exposed and scanned several more times to search for particles. Again, we didn’t see anything obvious. Then, as you may recall, something special happened in mid-November: […]



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