The “mole” aboard NASA’s InSight Mars lander has encountered stiff resistance on its first subsurface sojourn beneath the surface of the Red Planet.

In a major mission milestone, InSight’s Heat Flow and Physical Properties Package (HP3) instrument burrowed underground for the first time on Feb. 28. After 400 hammer blows over the course of four hours, the instrument apparently got between 7 inches and 19.7 inches (18 to 50 centimeters) beneath the red dirt — but obstacles slowed its progress, mission team members said.

“On its way into the depths, the mole seems to have hit a stone, tilted about 15 degrees and pushed it aside or passed it,” HP3 principal investigator Tilman Spohn, of the German Aerospace Center (known by its German acronym, DLR), said in a statement.

I’m digging #Mars! My self-hammering mole has started burrowing in, and my team is poring over the data I’ve sent them. They estimate it may be around 35 cm (14 in) down. More hammering to come, as I investigate the inside of Mars.?
More from @DLR_en: https://t.co/FsmfN0WVpa pic.twitter.com/CRHFDp6ouK

— NASA InSight (@NASAInSight) March 1, 2019

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