If your name starts with “L”, you’ll love this post about the first letter laser engraved on Mars. From time to time we see cartoons in which the rover rides in a pattern, leaving letters in the sand as wheel tracks. The letters make up a silly phrase, and the cartoon usually has aliens on the side that laugh or puzzle over the meaning. The use of lasers aboard the rovers has also made it possible to laser-mark graffiti on Martian rocks. Since NASA instruments are usually used exclusively for scientific purposes, I did not believe that laser graffiti would ever appear. But of course people thought about it. When I arrived at JPL for the Curiosity landing in 2012, I was surprised to find that one of our engineers in charge of developing sequences for the predecessor SuperCam had written a long sequence that used a laser to write the instrument’s name on a rock. surface. It was all in jest – we never wasted our footage using this sequence. However, at Perseverance we found a reason to use laser marking.
About two years ago I got a call from Professor Ben Weiss at MIT and asked about the possibilities of SuperCam laser marking. Ben has just joined Perseverance as part of the Sample Return Research Team, a group dedicated to collecting samples for return to Earth, with the goal of ensuring that samples are collected under appropriate conditions to optimize their scientific value upon return to Earth. Earth. Ben specializes in paleomagnetism. In terrestrial rocks, it is the study of the magnetism caused by the earth’s magnetic field during rock formation. Mars currently has a very weak magnetic field, but the strength of Mars’ field in the past is virtually unknown. Among other things, this has important implications for the retention or loss of the Martian atmosphere over time. Suffice it to say that we would like to use the samples returned from the Perseverance mission to fill this knowledge gap.
To do this, we need to know the original orientation of each returned Martian rock core sample. If the surfaces of these core samples have easily recognizable features, this is not a problem. So it was with the kernels collected so far. However, if the surface is fine-grained, there may be nothing to distinguish its rotational orientation. In this case, we need to make artificial markings on the surface.
We don’t have a dark marker, but we do have a pulsed laser. So a call from Ben to my lab a couple of years ago got us thinking about how to label nuclear samples, and we started some tests. JPL sent several stones of varying hardness to Los Alamos National Laboratory, where they were marked with pits made with varying numbers of laser shots. The stones were sent back to JPL for further coring.
Fast forward to summer 2022. The SuperCam team was asked to be ready to mark the rock for coring in just a few days. I was on SuperCam operations and seeing how soon we might need marks, we decided to switch from regular observation to a core marking sequence as a dry run. We have prepared various templates for the sign. The basic principle is to understand the rotational orientation of the core after it has been removed from the rock and placed in the sample tube. Any asymmetric pattern, for example, an arrow, is suitable for this. However, in order to be faster, we decided to use the simplest such pattern, consisting of three dots (or laser pits) with an unequal distance between them, like a capital letter “L”. SuperCam usually performs a line scan (single row) or a grid. To create the “L” shape, we took a 2×2 grid and removed one point from the sequence, so the laser made only three pits. Using 125 laser shots per hole, the result is shown in the picture of the Pinefield Gap target. Sample cores are 13 mm (0.5 in) in diameter, so the L-shapes should match well with their top surfaces. After a successful trial run, we are ready to use this procedure for labeling future samples.
Last week, Perseverance completed the second of two samples from the delta of Jezero Crater in the Skinner Ridge Block in Hogwallow Flats. Over the weekend, Perseverance drove about 25 meters to Wildcat Ridge, located a little lower in Hogwallow, for further exploration.
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