We have news from the Mars InSight mission that the mole instrument is finally all the way beneath the surface of Mars. This 16-inch (or 40-cm) long sensor was meant to pile drive itself three meters beneath the Martian surface and measure the heat profile of the soil as it went. I have to admit, more than any other Mars instrument in recent years, this was the instrument whose results I was most interested in seeing. 

The Martian soil both retains heat and protects everything beneath it from the harsh radiation of space. There have been myriad models that indicate that, depending on the temperature profile of the soil, it may be possible to have salty liquid water very close to Mars’ surface. Without actual data, however, all we can do is model what might be happening based on best-guess estimates of soil composition, density, and thermal behavior. The Insight mole was going to be the first real measurement of Mars soil at depth that we’ve ever had.

The only problem has been that Mars’ soil is so different from what was expected that the little probe has been unable to bury itself deep under the surface. Or even into the surface. 

This cylinder is designed with a pile driver inside that is slowly raised within the tube and then sent slamming downward. It should cause the mole to bury downward, like a shovel thrust into the ground, and ideally, friction should keep it at that new depth. This slow upward movement of the internal mechanism and rapid downward motion was extensively tested on Earth and proved itself excellent and digging through artificial Martian soil that was designed based on the characteristics of soils explored by other Mars missions.

The soil at the Mars Insight position, however, is more like clay, and the pile driver is bouncing upward instead of burying itself deeper. To get the mole completely underground, the mission team resorted to using the spacecraft’s shovel to push down on the mole while it tried to drive itself downward, and once it was close to the surface, they piled dirt on it and pushed with the shovel some more. There is still a glimmer of perhaps dying hope that the mole will break through the clays and enter soil that it can dig through as designed so it can complete its mission.

At this point, almost two years after arriving on Mars, I have to say I am in awe of the continued patience of this mission team. It is expected to take several months to pile enough dirt on top of the mole that the shovel will be able to effectively push down on it while it tries to dig. And they are just going to rearrange sand for those couple of months and do their best to get it down.

This is a slow and steady attempt to get the science done, and I wish this team all the luck in the world in getting their sensor buried.

More Information

NASA Jet Propulsion Laboratory press release