C. R. Ytsma

Laser‐induced breakdown spectra (LIBS) were collected on a diverse suite of ∼2,600 geological standards using four laser energies (2.4–7.2 mJ) to assess how variations in irradiance from stand‐off distance affect prediction accuracy. Mismatches in laser energies and plasma temperatures between training and prediction datasets introduce substantial uncertainty in major element predictions. For example, using 2.4 mJ spectra to predict 7.2 mJ data results in errors of ±8.9, ±1.4, ±3.8, ±3.2, ±1.6, ±1.0, ±0.6, and ±1.0 wt% for SiO 2 , TiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O, and K 2 O, respectively. When plasma temperatures of unknowns are represented in a multiple‐plasma‐temperature training set, prediction accuracies improve for the same oxides: ±3.0, ±0.3, ±1.3, ±1.4, ±1.0, ±0.7, ±0.5, and ±0.5 wt%. These results suggest that accuracies reported for Mars LIBS predictions based on single‐distance, single laser‐power calibration data may be overly optimistic except where Mars plasmas serendipitously match those acquired in the laboratory.