MicroLIBS: DEVELOPING A LIGHTWEIGHT ELEMENTAL MICRO-MAPPER FOR IN SITU EXPLORATION

Introduction: Recent instrument deployments have demonstrated the power of fine-scale composition analysis. It took the PIXL instrument onboard NASA’s Perseverance rover a single elemental map to prove the cumulate nature and alteration history of rocks in the Jezero crater floor [1]. In planetary exploration, a diversity of terrains have been observed from orbit or even in situ, yet remain of uncertain origin [2]. Micro-mapping can associate chemical composition with submillimeter-scale crystals, assemblages, mesostasis, fracture and void fills, and alteration phases in igneous rocks; and likewise, mineral grains, concretions and cements in fine-grained sedimentary rocks. These are all crucial to reconstruct the processes that generated these features.

Laser Induced Breakdown Spectroscopy (LIBS) is a technique that uniquely provides elemental abundances at submillimeter scales on naturally exposed rocks while removing surface dust. It can quantify the abundance of rocks major elements (Si, Fe, Mg, Al, Ca, K, Na, Ti) in addition to all light elements relevant to organics and volatiles (C, H, N, O, P, S) as well as other minor or trace elements (Li, Sr, Cr, Rb, Mn...), providing essential insights into geological processes of rocky and icy planetary surfaces.

Technology and heritage: LIBS is now widely used in the laboratory for micro-mapping, and on Mars we have a decade of experience with ChemCam [3] and now SuperCam [4] and MarsCoDe [5], which have proven the technique’s reliability and capability to analyze rocks geological investigations. It has been also test in lunar conditions [6]. However, none of these instruments were capable of fine-scale mapping. Miniaturization of LIBS systems has recently matured and now a set of handheld commercial devices ≤ 2 kg are available for  geochemical raster analyses [7]. Based on ChemCam/SuperCam heritage, we propose a new ≤ 1.5 kg instrument to perform LIBS micro-mapping.

Foreseen capabilities: µLIBS will operate at an adjustable distance of 20 to 50 cm. This shorter range, compared to ChemCam and SuperCam designs, enables significant mass reduction. Importantly, it will include a 2-axis actuated scanning mirror to enable both micro-mapping on areas < 1 cm² and analysis of multiple targets within an area below the platform without the need for a mast or gimbal (Fig. 1). It also includes a remote micro-imager and LED illumination to provide micro-textures with elemental grid overlaid. The ablated spot on target is within 50-100 µm diameter range, this tighter focus enable a lower laser pulse energy to generate signal. The µLIBS laser can also operate at up to 10 Hz, while dissipating less heat, making a typical 30x30 grid under 1 hour, with multiple laser shots on each point, efficiently removing dust from the target. These nearly 1000 grid points will help detect minor phases down to 0.1% of the rock and map their distribution. This novel capability enabling the detection of minor phases (e.g., potential zircons) which will be critical to refine current geological models based on major elements and phases only.

Ongoing development: The instrument prototype is currently being assembled at CNES with the production and delivery of most subsystems underway from IRAP, LANL, DLR and industry partners. The goal of this prototype is to verify the end-to-end performances, track the mass budget with a maximum allowance of 1.5 kg in our Mars configuration, and upgrade the TRL level close to 6 with dedicated tests in early 2026. While integration on the Mars Science Helicopter mission concept [8] implies a strict requirement on instrument mass, µLIBS technology can be adapted to in situ destinations including the Moon, icy moons and small bodies to fit other missions mass budget and accommodations (Fig. 1).

Conclusions: µLIBS can provide micro-scale elemental maps with a science return similar to contact instruments for lower cost, as it can operate remotely from a mobile platform undercarriage with no need for arm deployment nor platform turret. It is overall low risk (heritage-based), low mass, and low cost with significant improvements in terms of accuracy and rapidity.

References : [1] Liu Y. et al. (2022) Science 377, 1513–1519. [2](2023) Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032. [3] Maurice S. et al. (2016) J. Anal. At. Spectrom. 31, 863–889. [4] Wiens R. C. et al. (2022) Science Advances 8, eabo3399. [5] Xu W. et al. (2021) Space Sci Rev 217, 64. [6] Lasue J. et al. (2012) J. Geophys. Res. 117, E01002. [7] Senesi G. S. et al. (2021) Spectrochimica Acta Part B: Atomic Spectroscopy 175, 106013. [8] Fraeman A. A. et al. (2024) Tenth International Conference on Mars, abstract #3350.

 

Figure 1: µLIBS prototype design with compact opto-electronic assembly fits within a 10x15x20 cm envelope (left). Workspace targeting and micro-mapping with 30x30 points grid on target (red annotation, center). Examples of µLIBS accommodation onboard ~30 kg platforms (right). Background images: Curiosity rover and Apollo 17.