Curiosity Blog, Sols 4689-4694: Drill in the Boxwork Unit is GO!

Written by Catherine O’Connell-Cooper, APXS Payload Uplink/Downlink Manager, University of New Brunswick

Date of the earthworks plan: Friday October 17, 2025

Curiosity has been investigating the “cash unit” for several months. Readers may remember that we drilled on the edge of the caisson at “Altadena” last June. We have since traveled just under a kilometer through the caisson unit (approximately 0.6 miles) and are now ready to acquire the next drill target, in an area where the structure is really well preserved.

Box structures are a series of ridges and troughs, so our plan is to drill into one of the troughs and then onto one of the adjacent ridges. On Monday we completed our drilling rig on the “Valle de la Luna” in the “Monte Grande” trough – a multi-instrument undertaking. We evaluated the chemistry using APXS and ChemCam, to ensure it was within the expected range and not completely different from the bedrock compositions we tracked. Rover planners (RP) use a “preload” test, placing pressure on the bedrock surface to characterize the potential behavior of the rover arm and rock during drilling. We take multiple images (including images before and after the preload test), using MAHLI and Mastcam to help RPs assess the surface area of ​​the potential drilling area.

Finding a suitable place to drill into the troughs was a challenge, as the low point of each trough (which is what we are most interested in) is often covered in sand or small pebbles, with just sparse bedrock, as you can see in the attached image. However, we were lucky here in Monte Grande. The chemistry shows that this rock is within our expected compositional range. The MAHLI images show a smoother surface in the center of the brushed area (where the drill will focus), and the before and after images indicated that the rock responded well to the preload test. On Friday, the mission’s PRs and scientists pored over the data in a very intensive meeting called the Target Acquisition Assessment Meeting, or TAAM. We’ve drilled 43 holes on Mars now and it’s still nerve-wracking waiting to see if the information we gathered during our first science contact and preload gives us the green light. About halfway through the planning day we learned that TAAM had said yes to drilling here, so we will be drilling the first floor of this weekend plan.

If the exercise is successful, we will have no scientific contact for at least a week, as the arm cannot be deployed during an exercise campaign. Normally, as I am APXS PUDL (responsible for uplinking new APXS targets and downlinking evaluation of previous targets), the idea of ​​a week without scientific contact would disappoint me — but not during a drilling campaign! CheMin (Chemistry Mineralogy) and SAM (Sample Analysis at Mars) will use the drilled sample to provide us with deeper insights, examining the mineralogy and composition in a way that is not possible for APXS and ChemCam.

We can then use this drilling data to help us interpret the APXS and ChemCam data and better understand the formation of these caissons, especially if we can match them to a suitable target on the ridges.

In the meantime, we of course continue to monitor the atmosphere and environment around us. The Mastcam team is planning stunning images of this site and ChemCam will continue to characterize nearby bedrock and image distant hills.