Chapter 3 of 5

The stubborn soil

The heat probe’s struggle and the decision to stop digging

Told in InSight’s imagined voice · the events are real · source

NASA's InSight Mars lander took this final selfie on April 24, 2022, the 1,211th Martian day, or sol, of the mission.
InSightOne of my tools needed to go much deeper than my arm could reach.
NASA/JPL-Caltech
01The German-built HP³ mole was a self-hammering probe. Sensors in its tether were meant to measure heat flowing from inside Mars once it had dug at least three meters down.
The soil did not behave like the sand we expected.
02Instead of collapsing around the probe, the soil clumped. That deprived the mole of the friction it needed to keep its hammering from making it bounce back.
This is one of the last images ever taken by NASA's InSight Mars lander.
InSightPeople far away tried new jobs for my small scoop.
NASA/JPL-Caltech
03Engineers at JPL and DLR used my arm to help the mole and pack soil around it. Eventually its top was just below the surface—but being buried was not the same as reaching its science target.
We stopped the digging without pretending it had worked.
04On January 9, 2021, another 500 strokes made no progress. The deep heat-flow measurement was not achieved. The effort still taught scientists about local soil and engineers about digging on another world.

The big idea

An honest result includes what did not work. Soil behavior is part of an instrument’s engineering, not just its surroundings.

Think about it

Why did a working hammer still need help from the soil?

Fact file

Probe length
40 centimeters
Length of the mole itself, not its achieved digging depth.
Source ↗
Required depth
At least 3 meters
Needed for the intended deep heat-flow measurement, which was not achieved.
Source ↗
Final attempt
9 January 2021 / Sol 754
500 additional hammer strokes made no progress; the top was about 2–3 centimeters below the surface.
Source ↗

In this chapter: HP³ self-hammering mole, temperature-sensor tether and robotic scoop

Sources: Main record · InSight Spacecraft · NASA Science · NASA Retires InSight Mars Lander Mission After Years of Science

Machine illustration: AI-made. Photos: NASA Image and Video Library, credited on each picture.

Chapter 3 of 5

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