Applications of Raman spectroscopy technology in deep space exploration: A review

Raman spectroscopy acquires the molecular vibration spectra formed by non-elastic scattering of photons generated by laser excited materials. As "fingerprint" spectra of minerals and organic matters identification, Raman spectroscopy has been widely applied in the study of terrestrial and extraterrestrial samples, effectively obtaining key information such as mineral types, mineral chemistry, spatial distribution, rock and ore genesis, etc. It can accurately identify various minerals such as sulfates, chloride salts, layered silicates, and oxides in different hydration states, distinguish the differences in lattice structures between high-pressure phase minerals and low-pressure phase minerals. It can also describe the relationship between the stability and phase transition modes of various altered minerals and environmental parameters, and constrain the detection and identification of specific mineral phases on planetary surfaces based on the ground spectral libraries. In deep space exploration missions, Raman spectroscopy uses active laser excitation to obtain spectra, which has unique advantages in spectral signal acquisition and can effectively break through the constraints of planetary illumination conditions. Therefore, it is recommended for important exploration missions such as the Moon, Mars, asteroids, Venus, and ice satellites. China's Chang'e-7 mission will also be equipped with a Raman spectrometer to conduct in situ material composition detection in the southern region of the Moon. This review mainly discusses the main research progress of Raman spectroscopy in the field of planetary science and deep space exploration from the basic principles of Raman spectroscopy, research applications of extraterrestrial samples, and deep space exploration applications of Raman spectroscopy. In the basic physical principles of Raman spectroscopy, this review briefly introduces the principle and necessary conditions for the generation of Raman scattering light, provides an expression for the intensity of Raman scattering light, and lists the commonly used analytical methods in Raman spectroscopy quantification. At the end of the chapter, the schematic diagram of the Raman spectrometer and the application fields of Raman spectroscopy technology are also presented. In the application of extraterrestrial sample research, this review introduces the detailed research work on lunar soil, lunar meteorites, and Martian meteorite samples using Raman spectroscopy technology. By characterizing their mineral types, mineral patterns, mineral chemistry, and even impact history, the geological history of the samples can be understood. Raman spectroscopy technology can also monitor the mineral phase changes of minerals under different environmental parameters such as temperature and humidity, study the stable field, phase transition path, and dehydration process of minerals, in order to explore the environmental conditions during mineral formation. In this section, the Raman spectral and fingerprint characteristics of the main components are also summarized, serving the interpretation of Raman spectral data in subsequent engineering exploration missions. In the chapter on the application of Raman spectroscopy in deep space exploration, the scientific objectives, performance indicators, and instrument configurations of four main Raman spectrometer payloads (SHERLOC, SuperCam, RLS, RAX) are introduced. The limitations of Raman spectroscopy in deep space exploration are summarized, and the difficulties and challenges of Raman spectroscopy bringing to engineering exploration tasks are discussed in detail, focusing on the weak intensity of Raman scattering signals and fluorescence interference. At the end of the review, the future development trend of Raman spectroscopy technology in deep space exploration applications is also prospected, in order to provide useful references for future research and application of related payloads.