Concept and Design of Martian Far-IR ORE Spectrometer (MIRORES)

Abstract

Sulfide ores are a major source of noble (Au, Ag, and Pt) and base (Cu, Pb, Zn, Sn, Co, Ni, etc.) metals and will, therefore, be vital for the self-sustainment of future Mars colonies. Martian meteorites are rich in sulfides, which is reflected in recent findings for surface Martian rocks analyzed by the Spirit and Curiosity rovers. However, the only high-resolution (18 m/pixel) infrared (IR) spectrometer orbiting Mars, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), onboard the Mars Reconnaissance Orbiter (MRO), is not well-suited for detecting sulfides on the Martian surface. Spectral interference with silicates impedes sulfide detection in the 0.4–3.9 μm CRISM range. In contrast, at least three common hydrothermal sulfides on Earth and Mars (pyrite, chalcopyrite, marcasite) have prominent absorption peaks in a narrow far-IR (FIR) wavelength range of 23–28 μm. Identifying the global distribution and chemical composition of sulfide ore deposits would help in choosing useful targets for future Mars exploration missions. Therefore, we have designed a new instrument suitable for measuring sulfides in the FIR range called the Martian far-IR Ore Spectrometer (MIRORES). MIRORES will measure radiation in six narrow bands (~0.3 µm in width), including three bands centered on the sulfide absorption bands (23.2, 24.3 and 27.6 µm), two reference bands (21.5 and 26.1) and one band for clinopyroxene interference (29.0 µm). Focusing on sulfides only will make it possible to adapt the instrument size (32 × 32 × 42 cm) and mass (<10 kg) to common microsatellite requirements. The biggest challenges related to this design are: (1) the small field of view conditioned by the high resolution required for such a study (<20 m/pixel), which, in limited space, can only be achieved by the use of the Cassegrain optical system; and (2) a relatively stable measurement temperature to maintain radiometric accuracy and enable precise calibration.

Lunar ore geology and feasibility of ore mineral detection using a far-IR spectrometer

“…Here, prominent absorption peaks are displayed by most sulfides and oxides, including not only proposed previously (Ciazela et al, 2022) chalcopyrite, marcasite, and pyrite, which is ubiquitous in all planetary bodies but also ilmenite with the most vital line at 34.2 µm and troilite with the most vital line at 38.8 µm (Figure 6). In addition, we will measure two bands at 21.5 µm and 31.5 µm for reference (grey bands in Figure 6), with the latter differing from the Martian version (26.5 µm, Ciazela et al, 2022). The lunar version will also differ with the position clinopyroxene detector, measuring at 20.7 µm (purple band in Figure 6) in this case, which will make it possible to remove partial interference on pyrite from the secondary peak of clinopyroxene at ~23.8 µm using the following formula (Eq.…”

“…The last band will monitor pyrite-clinopyroxene interference (cf. Ciazela et al, 2022) at 20.7 µm (483 cm −1 ). Measuring only eight bands minimizes the dimensions (32 × 32 × 42 cm) and mass (<10 kg) to those required for microsatellites.…”

“…Using the linear mixing method analogical to the used by Ciazela et al (2022), we simulated various mixtures of ilmenite and a mixture of Ti-rich lunar basalt silicates (olivine, pyroxene, and plagioclase in a ratio of 5:50:30) to determine what would be the minimum amount of ilmenite needed to detect it from orbit (ratios of 1:9, 2:8, 3:7, and 4:6 of ilmenite to basalt were examined) (Figure 8A). Linear mixing of spectra is widely used in various scientific fields, from remote sensing to medicine and biology (Shi and Wang, 2014;De Angelis et al, 2017;Ciazela et al, 2022). Thermal IR spectra of multi-mineral surfaces can be modeled using linear combinations of the spectra of each mineral, weighted as percentages of the area occupied (Lyon, 1965;Thomson and Salisbury, 1993;Ramsey and Christensen, 1998).…”

“…However, even smaller mineralizations covering only a few square meters can be easily detected on the Moon with the MIRORES instrument thanks to its high resolution. Pyrite data has been provided and discussed by Ciazela et al (2022). To the best of our knowledge, other minerals are not measured for emmisivities due to a complex preparation procedure requiring temperature control (Ciazela et al, 2022).…”

“…Therefore, we propose a lunar version of the MIRORES (Multiplanetary far-IR Ore Spectrometer) instrument developed from its Martian version (Ciazela et al, 2022). MIRORES should be able to detect metal resources in sulfides and oxides also on Mars (Ciazela et al, 2022), where the low concentration of water in the atmosphere makes excellent conditions for FIR measurements, but the Moon is the most favorable environment for MIRORES, due to its extremely thin atmosphere, being technically just an exosphere. Therefore, MIRORES, which might be the world's first high-resolution far-infrared spectrometer for planetary research, will map various Moon resources during the Polish Lunar Mission.…”