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On NASA's InSight Mars lander a temperature probe nicknamed "Mole" is designed to hammer itself 5 meters into the ground and measure the temperature of the martian regolith at different depths with temperature probes mounted in its cable (Science Tether).

I found this very interesting PDF on how the mole hammers itself and how temperature is acquired. There's also a video of it hammering itself into a regolith analog here on earth.

enter image description here

Question: How does mission control decide where to place the "Mole" module? How can they ensure that it will be able to burrow to the full 5 meter depth without hitting some sort of hard rock or bedrock?

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  • $\begingroup$ Radio wave penetrate quite deep and one can construct a density map of ground then decide where to penetrate. Just like ultrasound. Though not sure if they use that. $\endgroup$ – Prakhar Apr 29 '18 at 15:07
  • $\begingroup$ @Prakhar Radar is sensitive to the distribution of permittivity or dielectric constant which is a lot different than sound conduction, so "just like ultrasound" is not really a good way to look at it. $\endgroup$ – uhoh Apr 29 '18 at 16:13
  • $\begingroup$ So far all I've found is that there's a camera which gives the lander a view of the "sensor deployment area" $\endgroup$ – Dragongeek Apr 29 '18 at 16:21
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At a post launch interview, one of the scientists talked about this and said that they worked together with many college students to analyse impact craters where the depth of regolith and bedrock layer can be seen. They then chose a site where they're pretty sure they've got at least 10 meters of sandy/dusty regolith with few rocks.

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