09:15 〜 09:30
[PPS09-02] Crater and Boulder Distributions on Deimos Revealed by Recent and Future Observations
★Invited Papers
キーワード：ダイモス、クレーター、ボルダー、火星圏
Deimos is one of the Martian satellites, characterized by its irregular shape and low-albedo surface [1]. Optical images from missions such as Viking, Mars Express, and Mars Reconnaissance Orbiter have revealed craters and boulders on Deimos, providing clues to both its surface evolution and its evolution within the Martian system [2, 3]. However, the global distribution of these geological features on Deimos has been unclear, due to the limited coverage and spatial resolution of previous images.
The Emirates Exploration Imager (EXI) onboard the Emirates Mars Mission (EMM) [4, 5] successfully obtained images of Deimos with relatively higher resolution and coverage on March 10, 2023. These images allow us to observe the global surface of Deimos, including the trailing and anti-Mars sides of the satellite, which have never been observed in detail. Here, we report the distributions of craters and boulders on Deimos, mapped with the EXI images.
We show that the power-law slope of the size frequency distribution of craters is close to -2. This may show that craters on Deimos may have reached a saturation equilibrium, suggesting Deimos has orbited near its current orbit for a long time. The leading side has slightly more craters than the trailing side, suggesting that tidal locking with Mars contributes to an asymmetric crater distribution, as observed on other tidally locked satellites such as Ganymede and Callisto. Moreover, the Mars-facing side contains more craters than the anti-Mars side, which is inconsistent with the expected reduction in impact flux due to the shielding effect of Mars. This finding suggests that Deimos may have temporarily broken tidal equilibrium and changed its orientation relative to Mars, possibly due to a large impact event that excavated the body, forming a large depression currently observed at the south pole. However, this should be further constrained by simulations of a large impact, its ejecta distribution, and its effect on the rotational state of the satellite.
We also find that boulders are more abundant on the anti-Mars side than on the trailing side. This result is consistent with that of the crater mapping, which suggests that a lower impact flux results in fewer craters and longer preservation of boulders. However, a comprehensive analysis of the global surface requires higher resolution and wider coverage images, which are expected from future missions such as the Martian Moons eXploration (MMX) [6, 7]. In this talk, we discuss the surface evolution of Deimos and its evolution in the Martian system from the crater and boulder distributions obtained from new EXI images and expected observations from the MMX mission scheduled for 2027.
References
[1] Pollack et al. (1972), JGR 78(20), 4313-4326. [2] Thomas et al. (1980), Icarus 41(3), 365-380. [3] Hirata (2017), Icarus 288, 69-77. [4] Amiri et al. (2022), SSR 218(1), 4, [5] Jones et al., (2021), SSR 217, 81. [6] Kuramoto et al., (2022), EPS 74(1), 12. [7] Nakamura et al., (2021), EPS 73(1), 227.
The Emirates Exploration Imager (EXI) onboard the Emirates Mars Mission (EMM) [4, 5] successfully obtained images of Deimos with relatively higher resolution and coverage on March 10, 2023. These images allow us to observe the global surface of Deimos, including the trailing and anti-Mars sides of the satellite, which have never been observed in detail. Here, we report the distributions of craters and boulders on Deimos, mapped with the EXI images.
We show that the power-law slope of the size frequency distribution of craters is close to -2. This may show that craters on Deimos may have reached a saturation equilibrium, suggesting Deimos has orbited near its current orbit for a long time. The leading side has slightly more craters than the trailing side, suggesting that tidal locking with Mars contributes to an asymmetric crater distribution, as observed on other tidally locked satellites such as Ganymede and Callisto. Moreover, the Mars-facing side contains more craters than the anti-Mars side, which is inconsistent with the expected reduction in impact flux due to the shielding effect of Mars. This finding suggests that Deimos may have temporarily broken tidal equilibrium and changed its orientation relative to Mars, possibly due to a large impact event that excavated the body, forming a large depression currently observed at the south pole. However, this should be further constrained by simulations of a large impact, its ejecta distribution, and its effect on the rotational state of the satellite.
We also find that boulders are more abundant on the anti-Mars side than on the trailing side. This result is consistent with that of the crater mapping, which suggests that a lower impact flux results in fewer craters and longer preservation of boulders. However, a comprehensive analysis of the global surface requires higher resolution and wider coverage images, which are expected from future missions such as the Martian Moons eXploration (MMX) [6, 7]. In this talk, we discuss the surface evolution of Deimos and its evolution in the Martian system from the crater and boulder distributions obtained from new EXI images and expected observations from the MMX mission scheduled for 2027.
References
[1] Pollack et al. (1972), JGR 78(20), 4313-4326. [2] Thomas et al. (1980), Icarus 41(3), 365-380. [3] Hirata (2017), Icarus 288, 69-77. [4] Amiri et al. (2022), SSR 218(1), 4, [5] Jones et al., (2021), SSR 217, 81. [6] Kuramoto et al., (2022), EPS 74(1), 12. [7] Nakamura et al., (2021), EPS 73(1), 227.