Quantitative olivine elemental and isotopic ratios from hypervelocity impact ionization TOF mass spectrometry

Impact-ionization time-of-flight mass spectrometry (II-TOF-MS) is a primary technique for in-situ compositional analysis of interplanetary and interstellar dust. However, quantitative elemental and isotopic interpretation requires laboratory validation against well-characterized standards across realistic encounter speeds.

We present hypervelocity dust-accelerator measurements of platinum-coated San Carlos olivine (Fo≈92) using the high-resolution reflectron-style Hyperdust II-TOF-MS. The olivine starting material was independently characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX), providing ground-truth Mg, Si, and Fe abundances and confirming low grain-to-grain compositional variability. More than 500 individual olivine projectiles were accelerated to encounter speeds spanning the regime relevant to modern spaceborne dust analyzers (≈10–25 km s⁻¹).

Time-domain spectra were analyzed by identifying major multiplets and fitting isotopic peaks with exponentially modified Gaussian line shapes to obtain integrated peak areas. Isotopic multiplets for Mg, Si, and Fe are resolved, and accepted spectra reproduce terrestrial isotope ratios within a defined tolerance, enabling robust peak deconvolution and contamination control. Using EDX-normalized relative sensitivity factors (RSFs), we convert ion intensities to elemental ratios and compare single-impact and ensemble results to the EDX composition.

At higher encounter speeds (≈19–25 km s⁻¹), RSF-corrected Mg/Si and Fe/Si ratios agree with the EDX values within uncertainties and cluster along the olivine compositional trend, with dispersion smaller than the separation between olivine and pyroxene in Mg–Fe–Si space. Ratios involving Si show stronger speed dependence at lower velocities, consistent with ionization effects and potential isobaric contributions near the Si region, while Mg/Fe remains comparatively stable.

These results provide a quantitative calibration benchmark demonstrating that high-resolution II-TOF-MS can recover elemental and isotopic information for silicate dust and can discriminate mineral families at encounter speeds typical of upcoming and current missions, including IDEX (IMAP), SUDA (Europa Clipper), and DDA (DESTINY+).