3:30 PM - 5:00 PM
[PPS06-P17] Development status of a laser-induced breakdown spectrometer for lunar exploration
Keywords:Lunar exploration, LIBS, In situ Analysis
Lunar exploration programs have been planned by various countries in this decade, and opportunities for both unmanned and manned exploration are rapidly developing. JAXA is currently developing the SLIM pinpoint landing demonstrator and the LUPEX lunar polar explorer, and internationally the ARTEMIS project is planned to send astronauts to the Moon. From a scientific perspective, detailed analysis by sample return has significant advantages, and to maximize their benefits, it is important to select key rocks in situ on the lunar surface: impact melt rocks from the formation of impact basins to determine the age of the Great Planetary Migration, and primordial crust rocks with old solidification ages to determine the formation process of the Moon [1]. To identify such samples effectively, we have developed instruments using Laser-Induced Breakdown Spectroscopy (LIBS).
LIBS is an elemental analysis technique in which a sample is partially irradiated with laser pulses to induce plasma, and the element-specific emission lines of de-excited electrons are measured with a spectrometer. It enables rapid measurements from a remote distance without sample preparation. Because of its advantages suitable for in-situ analysis, it has been used on Mars rovers by the US and China [2][3][4]. The tentative specification of our LIBS instrument under development is as follows. The instrument would be mounted on a rover or lander and measures the wavelength range of 370-780 nm and enable detection of major elements (Si, Fe, Mg, Ca, Al, Na, Ti, K), trace elements (Cr, Mn, Ni) and volatile elements (H, C, O) in rocks. The high spatial resolution of the laser (~500 µm) allows analysis of distant samples (1-3 m) in a short time (~ several minutes). The laser ablation also enables sample analysis while excavating the sample on a millimeter scale. This capability makes it possible to remove regolith and space weathering layers covering the surface and obtain chemical composition data of the target rock.
A tentative operational flow of this system is as follows: (1) Capture images of the structure and state of the measured object by a coaxial microscopic imager (pixel resolution 15 um/pixel), (2) Adjust the position of the objective lens based on the imager data to focus Nd:YAG laser beam, (3) Irradiate laser pulses about 100 times per spot, and then obtain emission spectra, (4) Identify rock types and obtain elemental distribution map of the object by moving scan mirror to change the field of view and irradiation position. The obtained spectra will be analyzed by partial least squares (PLS) regression using our spectral library of various geological samples as a model for elemental quantification. From the hydrogen spectrum, water presence of lunar rocks, which is especially relevant in terms of manned exploration, can be estimated [5]; thus as a further development, we also examined a laser ablation molecular isotope spectroscopy (LAMIS) system that enables analysis of OH molecular emission in the ultraviolet region simultaneously with LIBS, to increase the accuracy of the water measurements. With these developments, we aim to obtain geological data on the Moon, which is necessary for both the scientific study of the solar system evolution and for future manned lunar activities.
[1] Morota, T. et al. (2023) this conference, [2] Wiens, R.C. et al. (2012) Space Sci. Rev., 170, 167-227. [3] Wiens, R.C. et al. (2021) Space Sci. Rev., 217, 4. [4] Wan, X. et al. (2021) Atomic Spectrosc., 42, 294-298. [5] Yumoto, K. et al. (2023) SSRN Electronic Journal. 10.2139/ssrn.4347435.
LIBS is an elemental analysis technique in which a sample is partially irradiated with laser pulses to induce plasma, and the element-specific emission lines of de-excited electrons are measured with a spectrometer. It enables rapid measurements from a remote distance without sample preparation. Because of its advantages suitable for in-situ analysis, it has been used on Mars rovers by the US and China [2][3][4]. The tentative specification of our LIBS instrument under development is as follows. The instrument would be mounted on a rover or lander and measures the wavelength range of 370-780 nm and enable detection of major elements (Si, Fe, Mg, Ca, Al, Na, Ti, K), trace elements (Cr, Mn, Ni) and volatile elements (H, C, O) in rocks. The high spatial resolution of the laser (~500 µm) allows analysis of distant samples (1-3 m) in a short time (~ several minutes). The laser ablation also enables sample analysis while excavating the sample on a millimeter scale. This capability makes it possible to remove regolith and space weathering layers covering the surface and obtain chemical composition data of the target rock.
A tentative operational flow of this system is as follows: (1) Capture images of the structure and state of the measured object by a coaxial microscopic imager (pixel resolution 15 um/pixel), (2) Adjust the position of the objective lens based on the imager data to focus Nd:YAG laser beam, (3) Irradiate laser pulses about 100 times per spot, and then obtain emission spectra, (4) Identify rock types and obtain elemental distribution map of the object by moving scan mirror to change the field of view and irradiation position. The obtained spectra will be analyzed by partial least squares (PLS) regression using our spectral library of various geological samples as a model for elemental quantification. From the hydrogen spectrum, water presence of lunar rocks, which is especially relevant in terms of manned exploration, can be estimated [5]; thus as a further development, we also examined a laser ablation molecular isotope spectroscopy (LAMIS) system that enables analysis of OH molecular emission in the ultraviolet region simultaneously with LIBS, to increase the accuracy of the water measurements. With these developments, we aim to obtain geological data on the Moon, which is necessary for both the scientific study of the solar system evolution and for future manned lunar activities.
[1] Morota, T. et al. (2023) this conference, [2] Wiens, R.C. et al. (2012) Space Sci. Rev., 170, 167-227. [3] Wiens, R.C. et al. (2021) Space Sci. Rev., 217, 4. [4] Wan, X. et al. (2021) Atomic Spectrosc., 42, 294-298. [5] Yumoto, K. et al. (2023) SSRN Electronic Journal. 10.2139/ssrn.4347435.