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The scattering properties of terrestrial planetary bodies can provide valuable insights into their shallow seismic structure, meteoritic impact history, and geological activity. Scattering properties of the shallow crusts of Earth, Mars, and the Moon are investigated by constructing P‐wave receiver functions (PRFs) from teleseismic waveforms with high signal‐to‐noise ratios. The authors' analysis reveals that strong coda waves lead to significant variations in the PRF waveforms calculated using different time windows, and the stability of the PRF is primarily influenced by the fractional velocity fluctuation. Synthetic PRFs for various scattering media confirm these observations. Comparing the observed and synthetic PRFs, it is found that the fractional velocity fluctuation in the shallow crust is greater than ∼0.2 for the Moon but less than ∼0.2 for Earth and Mars. The authors further discuss possible mechanisms that could have affected the fractional velocity fluctuation and suggest that the distinct fractional velocity fluctuation between the Moon and Earth/Mars is mainly due to differences in the water content of the crustal rocks of the three planetary bodies. Plain Language Summary: Coda waves follow direct P or S waves and comprise scattered waves generated when seismic waves travel through a heterogeneous medium. These incoherent coda waves may interfere with seismic waves from coherent structures and complicate the interpretation of seismic structures. The authors compute P‐wave receiver functions (PRFs) of Earth, Mars, and the Moon using teleseismic waveforms with high signal‐to‐noise ratios. It is found that the PRFs of Earth and Mars are reliable and that the crustal converted waves can be effectively recovered. However, the PRF of the Moon calculated using different time windows is unstable even for direct P waves. The authors demonstrate that the stability of the PRF can be used to characterize the strength of the seismic scattering. Increased scattering by the medium leads to the degradation of the PRF stability. The PRF stability is mainly affected by the fractional velocity fluctuation of the shallow crust, which is larger on the Moon than on Earth and Mars. The fractional velocity fluctuation of the shallow crust is smaller on Earth and Mars because their shallow crusts are hydrous, whereas the shallow crust of the Moon is anhydrous. Key Points: The stability of a P‐wave receiver function degrades with increasing fractional velocity fluctuation of the shallow crustThe fractional velocity fluctuation of the shallow crust is larger on the Moon than on Earth and MarsThe water content of the crustal rocks is the main factor responsible for the different fractional velocity fluctuations [ABSTRACT FROM AUTHOR]

The intense seismic scattering seen in Apollo lunar seismic data is one of the most characteristic features, making the seismic signals much different from those observed on the Earth. The scattering is considered to be attributed to subsurface heterogeneity. While the heterogeneous structure of the Moon reflects the past geological activities and evolution processes from the formation, the detailed description remains an open issue. Here, we present a new model of the subsurface heterogeneity within the upper lunar crust derived through a full 3D seismic wave propagation simulation. Our simulation successfully reproduced the Apollo seismic observations, leading to a significant update of the scattering properties of the Moon. The results showed that the scattering intensity of the Moon is about 10 times higher than that of the heterogeneous region on the Earth. The quantified scattering parameters could give us a constraint on the surface evolution process of the Moon and enable the comparative study for answering a fundamental question of why the seismological features are different on various planetary bodies. Plain Language Summary: In the past Apollo missions, several seismometers were installed on the nearside of the Moon and they brought us the first seismic records from an extraterrestrial body. The derived lunar seismic data surprised us because of their extremely long duration (1–2 hr) and spindle‐shaped form, which were barely observed on Earth. These characteristics, which are different from earthquakes, are thought to reflect the subsurface heterogeneity. However, the inhomogeneous structure within the lunar crust is poorly constrained. To improve our knowledge of wave propagation on an extraterrestrial body, this study evaluated the subsurface heterogeneity through 3D seismic wave propagation simulation. After running some simulations under various structure settings, we found that a certain set of parameters well reproduced the Apollo seismic data, resulting in a new heterogeneous structure model of the Moon. The evaluated parameters were compared with those measured on the Earth and Mars, and we found that the Moon is more heterogeneous than others by about 10 times. This kind of comparison makes it easier to interpret the observed seismic signals on each solid body. Also, it is useful to explain the differences in their surface evolution scenarios. We believe that our results contribute to further extending comparative planetology. Key Points: Through full 3D seismic wave propagation simulation, we quantitatively evaluated the lunar seismic scattering propertiesWe found that a 10‐km thick scattering layer with 10% velocity fluctuation well‐reproduced the Apollo seismic observationOur results show that the upper lunar crust is about 10 times more heterogeneous than that of the Earth and Mars [ABSTRACT FROM AUTHOR]

Abstract: Iapetus, one of the saturnian moons, has an extreme albedo contrast between the leading and trailing hemispheres. The origin of this albedo dichotomy has led to several hypotheses, however it remains controversial. To clarify the origin of the dichotomy, the key approach is to investigate the detailed distribution of the dark material. Recent studies of impact craters and surface temperature from Cassini spacecraft data implied that sublimation of H2O ice can occur on Iapetus’ surface. This ice sublimation can change the albedo distribution on the moon with time. In this study, we evaluate the effect of ice sublimation and simulate the temporal change of surface albedo. We assume the dark material and the bright ice on the surface to be uniformly mixed with a certain volume fraction, and the initial albedo distribution to incorporate the dark material deposits on the surface. That is, the albedo at the apex is lowest and concentrically increases in a sinusoidal pattern. This situation simulates that dark materials existed around the Iapetus’ orbit billions of years ago, and the synchronously rotating Iapetus swept the material and then deposited it on its surface. The evolution of the surface albedo during 4.0Gyr is simulated by estimating the surface temperature from the insolation energy on Iapetus including the effect of Saturn’s eccentricity and Iapetus’ obliquity precession, and evaluating the sublimation rate of H2O ice from the Iapetus’ surface. As a result, we found that the distribution of the surface albedo changed dramatically after 4.0Gyr of evolution. The sublimation has three important effects on the resultant surface albedo. First, the albedo in the leading hemisphere has significantly decreased to approach the minimum value. Second, the albedo distribution has been elongated along the equator. Third, the edge of the low albedo region has become clear. Considering the effect of ice sublimation, the current albedo distribution can be reconstructed from the sinusoidal albedo distribution, suggesting the apex–antapex cratering asymmetry as a candidate for the origin of the albedo dichotomy. From the model analysis, we obtained an important aspect that the depth of the turn-over layer where the darkening process proceeded for 4Gyr should be an order of 10cm, which is consistent with evaluation from the Cassini radar observations. [Copyright &y& Elsevier]