"Impact crater yield dating" is the main method to study the age of planet surface at present, but this method has low accuracy and big error, and it can't distinguish the ages of different lithology in the same area. In 20 12, the American Curiosity Mars probe first applied the K-Ar isotope dating method to the dating of Martian surface materials, which opened a new era of in-situ dating of planetary surface isotopes. However, Curiosity does not carry a so-called "dating instrument". Its K and Ar contents are analyzed by a general geochemical subsystem, and finally the age is calculated. As far as reliable age determination is concerned, there are several problems in its method: first, it is impossible to determine the reliability of age because of the single determination; Secondly, the whole rock sample is heated to extract gas, ignoring the problem of sample heterogeneity; Thirdly, the temperature of pyrolysis furnace is limited, which leads to incomplete gas extraction and low age; Finally, because the "initial Ar" cannot be deducted, we have to assume that all Ar in the sample is radioactive Ar accumulated after the formation of minerals, so the geological significance of this age is very unclear.
In order to solve the above problems, Faye Wong, a researcher from the Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, China Academy of Sciences, cooperated with Li Baoquan, a researcher from the International Space Science Center of China Academy of Sciences. Based on the successful experience and problems exposed in the international deep space exploration program, a new in-situ dating method of planet surface is proposed, and a dating scheme suitable for special conditions of deep space exploration (Figure 1) is designed and developed, which provides a guarantee for the upcoming deep space exploration tasks such as extraterrestrial planet exploration and lunar science base in China.
The scheme adopts laser-induced breakdown plasma spectroscopy and quadrupole mass spectrometry (LIBS-QMS). Based on the new method "Laser Diluent-Free K-Ar Method" proposed by Faye Wong's research team and the invention patent "A laser sample chamber suitable for deep space exploration", the K content and Ar isotope composition were simultaneously determined by the sensitivity characteristic curve method, and finally the reliable K-Ar age was obtained. The scheme also describes the influence of hydrocarbons and hydrogen chloride widely existing in extraterrestrial planetary materials on Ar isotope determination and its correction method.
This scheme gives full play to the characteristics of high temperature and high efficiency of laser sampling, and analyzes the same sample for many times, so as to obtain the "absolute" age by using the inverse isochron method, which overcomes a series of problems existing in Curiosity technology. At present, the ground verification system is under development.
The research results were published in the domestic academic journal Bulletin of Mineral Rock Geochemistry (Faye Wong, Yang Liekun, Shi Wenbei, Wang). K-Ar Dating for Deep Space Exploration of Planetary Surface: Techniques and Methods [J]. Bulletin of Mineral and Rock Geochemistry, 202 1, 40 (6):1304-1312. DOI: 10. 19658/j . ISSN . 1007-2802.202 1.40 . 09 1)。
Editor: Chen Feifei
Proofreading: Jiang Xuejiao