Taichi Kawamura

Determining the crust–mantle boundary of the Moon has been an important topic in lunar interior studies. However, strong seismic scattering in the lunar subsurface has made it challenging to identify clear crustal reflections or converted seismic phases. In addition, the limited epicentral distances of recorded moonquakes restrict direct constraints on the lunar crust from first‐arriving seismic waves. Consequently, the Moon's crustal structure remains poorly constrained due to the limited availability of seismological evidence. Through joint analysis of seismic, topographic, and gravity data, while accounting for seismic velocity variations predicted by thermal modeling, we obtain new ray tracing results and present new insights on the lunar crust and upper mantle structure. Our results constrain the average global Moho depth to 35.1 2.6 km. Additionally, our results indicate slightly lower seismic velocities in the uppermost mantle than previously estimated, at approximately 7.5 km/s. Introducing the thermal model into the inversion further allows us to constrain the Moon's surface heat flow, with an average value of 10.7 0.8 , which is consistent with the heat flow measurements obtained during the Apollo mission. The refined crustal thickness provides a structural basis for estimating the Moon's bulk Al and Th abundances. The model also better constrains the porosity, density, and radiogenic heat production of the lunar crust, and provide new implications for a pyroxene‐rich upper mantle composition.

Meteoroid impacts are frequent on the Moon and provide valuable natural seismic sources for probing the lunar interior. However, accurately locating lunar impacts remains challenging because intense scattering within the highly fractured lunar crust obscures direct P- and S-wave arrivals. Coda-based localization methods exploit scattered energy, but their accuracy has so far been limited by the parameterization of the method. In this study, we reformulated a coda-based localization approach within the framework of seismic quanta scattering theory by introducing four distance proxies: peak amplitude, rise time, differential arrival time, and the overall coda shape. By jointly combining these proxies, we obtain locations that agree well with independent travel-time-based solutions. We then apply the method to locate forty-nine high-amplitude local impact events recorded by the Apollo seismic network, while also estimating their localization uncertainties and impact momenta. Our results demonstrates that coda waves contain robust distance information even in a strongly scattering lunar crust, enabling reliable impact localization and providing new constraints on the connection between seismic source properties and impact crater formation.

Determining marsquake magnitudes is essential for assessing seismic activity on Mars, yet previous estimates neglect three‐dimensional (3D) scattering effects. The exceptionally long‐lasting coda of the largest recorded marsquake, S1222a, provides a unique opportunity to quantify how crustal heterogeneities affect waveform propagation and magnitude estimation. Here, we perform full 3D waveform simulations for S1222a, incorporating surface topography, lateral crustal thickness variations, and heterogeneous random media. By fitting waveform envelopes in the 0.04–0.08 Hz frequency band, crustal heterogeneities with 20–50 km correlation lengths and 30%–40% maximum velocity perturbations are required to reproduce the observed long‐period scattered surface waves. Accounting for these 3D scattering effects increases the estimated moment magnitude of S1222a to 4.7–4.9, higher than one‐dimensional (1D) estimates and consistent with normal mode observations. Our results demonstrate that neglecting 3D scattering can systematically underestimate marsquake magnitudes by 0.2–0.3, biasing estimates of seismic energy release on Mars.

Intrinsic attenuation in planetary ices remains poorly constrained at seismic frequencies and low temperatures, limiting quantitative predictions of wave propagation in icy moons. Existing models typically rely on constant‐Q, or power‐law formulations that lack microphysical grounding and fail to capture the strong temperature sensitivity of ice Ih. Here, we develop a physics‐based attenuation model that combines dislocation relaxation, grain‐boundary sliding, and proton reorientation mechanisms within a unified Cole‐SAS‐Maxwell framework, providing a consistent transition between seismic and tidal frequency regimes. The model is calibrated against laboratory and semi‐empirical constraints over a broad range of homologous temperatures (0.34–1 for ice Ih; 94 K–273 K in absolute temperature) and pressures up to 100 MPa. The proposed framework predicts order‐of‐magnitude variations in intrinsic shear attenuation across icy‐shell thermal profiles and provides a quantitative framework for assessing wave dispersion, energy loss, and seismic detectability in the shells of Titan‐like satellites.

Intrinsic attenuation in planetary ices remains poorly constrained at seismic frequencies and low temperatures, limiting quantitative predictions of wave propagation in icy moons. Existing models typically rely on constant-Q, or power-law formulations that lack microphysical grounding and fail to capture the strong temperature sensitivity of ice Ih. Here, we develop a physics-based attenuation model that combines dislocation relaxation, grain-boundary sliding, and proton reorientation mechanisms within a unified Cole-Maxwell-SAS framework, ensuring a consistent transition between seismic and tidal frequency regimes. The model is calibrated against laboratory and semi-empirical constraints over 94–273 K and pressures up to 100 MPa. The results predict order-of-magnitude variations in intrinsic shear attenuation across icy-shell thermal profiles, and provide a quantitative framework for assessing wave dispersion, energy loss, and seismic detectability in the shells of Titan-like satellites.

The Next Generation small-body Sample Return (NGSR) is a Japanese strategic large-class science mission candidate in the 2030s. Following Hayabusa, Hayabusa2, and upcoming Martian Moons eXploration (MMX), NGSR is planning to return samples from a Solar System primitive body. The samples returned by Hayabsua2 from the C-type asteroid Ryugu indicated the evolution process from its parent body and the transport of materials in the early Solar System [1]. However, the ultimate origin of the Solar System material and the formation of the first-generation planetesimals still remain unsolved. Thus, the science goals of NGSR include (1) unveiling the origin of the Solar System materials in galactic evolution and (2) unveiling the origin of the Solar System bodies to form planetesimals. To achieve these goals, we propose the NGSR Origins program targeting comets (NGSR-C), D-type asteroids (NGSR-D), and E-type asteroids (NGSR-E). The comet (e.g., 289P/Blanpain) is the target to investigate the origin of materials from pre-solar era and the formation process of planetesimals in the outermost Solar System. The D-type asteroid (e.g., 2001 SK162) is to constrain the evolution of organic matter and the formation process of planetesimals in the outer Solar System. The E-type asteroid (e.g., 4660 Nereus) is to investigate the evolution of materials in the innermost region of the Solar System and the formation process of inner Solar System. NGSR is strongly constrained by use of an H3 rocket and a Deep-Space Orbital Transfer Vehicle (DS-OTV) [2], a newly developing transportation system to be commonly used for many missions. The NGSR spacecraft system consists of a DS-OTV as the main spacecraft and a lander for sample collection [2]. A concept study assumes its launch in early half of 2030s, arrival at the target for exploration, and return of samples to Earth within 6~8 years (NGSR-E or -D) to 13 years (NGSR-C). The mission instruments are categorized into four types: (1) remote sensing instruments for characterization of the target body and the landing site selection, including an optical navigation camera, a laser altimeter, and a thermal infrared imager. (2) sample return devices: A bullet and/or pneumatic type sampler on the lander, a kinetic impactor, and a mass spectrometer on the lander to measure volatiles on-site. Most of the collected samples will be transferred to the reentry capsule on the DS-OTV after sampling and rendezvous docking of the lander to the DS-OTV. (3) interior structure measurements: bistatic radar system, and small landing seismometer units deployed onto the surface. (4) other optional instruments to improve the scientific significance of this mission, including a near infrared spectrometer, a 10kg-sized small scientific deployable probe like the Hayabusa2 MASCOT, and a small dust and volatile detector as international collaboration. There remains an opportunity for the other instruments before the final decision of instruments. We will present the mission design, science operation, and instruments at that time. [1] e.g., Nakamura T. et al. (2022) Science, 90, eabn8671.[2] Saiki T. et al., (2025) Acta Astronaut., 235, 120-128.

Among the reported seismic events on the Moon, shallow moonquakes are known for their unique features, such as high‐frequency energy excitation, similarity to intraplate earthquakes, and the largest energy release of all reported moonquakes. Despite these interesting features, a small number of samples (<80 events) and sparse seismic network observations prevented us from gaining an in‐depth understanding of shallow moonquakes. In this study, by using the Apollo 17 gravimeter as a pseudo‐seismometer, we extend the Apollo lunar seismic network and located a few shallow moonquakes more accurately. In addition, comparing the located shallow‐moonquake epicenters with surface/subsurface geological features indicates that at least one event may be better explained by deep‐seated faults within the crust. Along with a previous demonstration of low‐frequency moonquakes, our analysis of high‐frequency events shows that the Apollo 17 gravimeter can serve as a seismometer over a broader frequency range than previously considered.

The internal structure of the Moon is key to understanding its formation, evolution, and bulk composition. In particular, determining the structure of the crust–mantle interface (Moho), including its lateral variations, is of significant importance, but current knowledge is still insufficient to fully constrain it. To address this, we used seismic wave arrivals from impact events, which yield constraints on the crust at both the impact sites and the Apollo stations, to invert for local crustal thickness. Based on a series of assumed crust and mantle density models, we compared Moho depths inferred from global gravity recovery and interior laboratory gravity data with those from seismic observations. Although the gravity‐derived results broadly capture the overall Moho relief, local discrepancies remain, with differences reaching up to 10 km in the vicinity of the Apollo 17 Saturn IVB impact site. These results may reflect regional geological anomalies and highlight the importance of incorporating multiple seismically constrained crustal thickness estimates as anchors in gravity inversions. Using seven seismic anchor points and assuming an upper mantle velocity of 7.68 , an upper mantle density of 3,280 , and a crustal density of 2,693 , we obtain an average lunar crustal thickness of 43.6 1.9 km. The findings also provide valuable guidance for future global 3D modeling of the Moon.

Detecting seismic activity on Saturn's icy moon Titan during the Dragonfly mission could provide crucial information on its internal structure. The geological complexity of the moon's surface suggests significant cyclic tidal deformation, likely leading to the fracturing of the ice shell. Considering realistic source locations and fault geometries, we assess whether a vertical short‐period seismometer can detect body waves from a 4.0 icequake. Signal‐to‐noise ratios are evaluated by comparing the high‐frequency content with the expected background noise and instrument capabilities for several ice attenuation scenarios and 1D interior models. Our results indicate that the high‐frequency content (Hz) of tidal‐induced icequakes is likely undetectable under the most unfavorable attenuation scenarios and atmospheric conditions. However, seismic signals in the 0.5–1 Hz band—where P wave reflections dominate—may still be observable for events occurring in potential seismically active regions at ∼800–1,000 km from the Dragonfly 's landing site. These signals could provide constraints on the thickness of Titan's outer ice shell, provided that intrinsic attenuation is low and environmental conditions are favorable.

More than 50 years after Apollo, the Moon deep interior structure is still not well known. Several seismic experiments are expected on the Moon surface in the coming year (Chang’e 7, Chandrayan, Artemis III, FSS and SPSS). All of those seismometers are not expected to resolved the seismic background of the Moon and their performances are not meeting the International Lunar Network requirements (10-11 m.s-2/sqrt(Hz)).To meet this requirement, IPGP is developing an optical seismometer operated in open loop. Its mechanical oscillator is a 1Kg proof mass suspended by a 4 cross blades hinge and a leaf spring with extremely low damping. Its displacement sensor is a Michelson interferometer, associated to a narrow bandwidth laser source and an optical phase readout electronic inherited from fiber optics gyroscope. This instrument will be candidate for all flight opportunities around 2030 (launch date).The first prototypes performances tests demonstrated the potential of this technology. But it also revealed that stray light inside the interferometer is limiting its performance. Different techniques of characterization of the stray light are compared: in situ coherent detection, characterization using a delay line and short coherency length light source. Tests results are compared to simulation.Analysis of the stray light impact on the performances through the optical phase readout electronic modulation scheme shows the impact on performances. Expectation and performances potential of the next prototypes generation is discussed.