Developing Prototype Simulants for Surface Materials and Morphology of Near Earth Asteroid 2016 HO3

There are a variety of applications for asteroid simulants in asteroid studies for science advances as well as technology maturation. For specific purpose, it usually requires purpose-specialized simulant. In this study, we designed and developed a set of prototype simulants as S-type asteroid surface materials analogue based on H, L, and LL ordinary chondrites’ mineralogy and terrestrial observations of near-earth asteroid 2016 HO3, which is the Chinese sample return mission target. These simulants are able to simulate morphology and reflectance characteristics of asteroid (469219) 2016 HO3 and, thus, to be used for engineering evaluation of the optical navigation system and the sampling device of the spacecraft during the mission phase. Meanwhile, these prototype simulants are easily to modify to reflect new findings on the asteroid surface when the spacecraft makes proximate observations.

SinGAN-Based Asteroid Surface Image Generation

While it is risky considering spacecraft constraints and unknown environment on asteroid, surface sampling is an important technique for asteroid exploration. One of the sample return missions is to seek an optimal landing site, which may be in hazardous terrain. Since autonomous landing is particularly challenging, it is necessary to simulate the effectiveness of this process and prove the onboard optical hazard avoidance is robust to various uncertainties. This paper aims to generate realistic surface images of asteroids for simulations of asteroid exploration. A SinGAN-based method is proposed, which only needs a single input image for training a pyramid of multi-scale patch generators. Various images with high fidelity can be generated, and manipulations such as shape variation, illumination direction variation, super resolution generation are well achieved. The method's applicability is validated by extensive experimental results and evaluations. At last, the proposed method has been used to help set up a test environment for landing site selection simulation.

The role of regolith thickness in seismic shaking on asteroids

<p>Near-Earth Asteroids visited by spacecraft display a depletion in the number of small craters (< 100 m). For example, the fractured monolith 433 Eros (Thomas et al., 2005), and the rubble piles 25143 Itokawa (Michel et al., 2009), 162173 Ryugu (Noguchi et al., 2021), and 101955 Bennu (Daly et al., 2020) all show a depletion in small craters. Models of the crater populations on Eros and Itokawa indicate that the depletion can be explained by seismic shaking induced by meteorite impacts (e.g., Thomas et al., 2005; Richardson et al., 2004; 2005; Michel et al., 2009). The effects of seismic activity occur in the active layer, the uppermost layer of the regolith. Previous models of seismic shaking that recreate crater populations have used a broad range of active layer depths, ranging from 0.1 m to 5 m across various models for Itokawa and Eros (Richardson et al., 2004; 2005; 2020; Michel et al 2009; Susorney et al., 2021). However, the actual regolith thickness is poorly constrained or unknown in many cases.</p> <p>In this study, the uncertainty introduced into seismic shaking models from the assumed active layer thickness is investigated by comparing the relative timescales of crater relaxation (crater erasure). We use the Richardson et al., (2004) seismic shaking model, as modified by Michel et al., (2009) for Itokawa with impactor populations from O’Brien and Greenberg (2005). Our results show that decreasing the active layer depth leads to a nonlinear increase in the time to erase a crater. The total increase in time to erasure for a crater 20 m in diameter when changing from regolith depths of 5 m to 0.1 m is over three magnitudes, mostly accommodated between depths of 1 m to 0.1 m. We also investigated the relative timescales of crater erasure for craters of different sizes. Increasing the crater diameter leads to a non-linear increase in crater erasure time, with a 10<sup>3</sup> increase in erasure time when the diameter is increased from 5 m to 100 m.</p> <p>The high sensitivity of crater erasure time on active layer depth and crater size implies that care should be taken when inferring surface properties, in particular asteroid surface age, time since a resetting event, or depth/diameter comparisons between asteroids with different crater populations.</p> <p> </p> <p>References</p> <p>                  Daly, R.T., Bierhaus, E.B., Barnouin, O.S., Daly, M.G., Seabrook, J.A., Roberts, J.H., Ernst, C.M., Perry, M.E., Nair, H., Espiritu, R.C., Palmer, E.E., Gaskell, R.W., Weirich, J.R., Susorney, H.C.M., Johnson, C.L., Walsh, K.J., Nolan, M.C., Jawin, E.R., Michel, P., Trang, D., Lauretta, D.S., 2020. The Morphometry of Impact Craters on Bennu. Geophys. Res. Lett. 47, e89672. doi:10.1029/2020GL089672</p> <p>Michel, P., O'Brien, D.P., Abe, S., Hirata, N., 2009. Itokawa's cratering record as observed by Hayabusa: Implications for its age and collisional history. Icarus 200, 503–513. doi:10.1016/j.icarus.2008.04.002</p> <p>Noguchi, R., Hirata, N., Hirata, N., Shimaki, Y., Nishikawa, N., Tanaka, S., Sugiyama, T., Morota, T., Sugita, S., Cho, Y., Honda, R., Kameda, S., Tatsumi, E., Yoshioka, K., Sawada, H., Yokota, Y., Sakatani, N., Hayakawa, M., Matsuoka, M., Yamada, M., Kouyama, T., Suzuki, H., Honda, C., Ogawa, K., Kanamaru, M., Watanabe, S.-I., 2021. Crater depth-to-diameter ratios on asteroid 162173 Ryugu. Icarus 354, 114016. doi:10.1016/j.icarus.2020.114016</p> <p>O'Brien, D.P., Greenberg, R., 2005. The collisional and dynamical evolution of the main-belt and NEA size distribution, Icarus 178, 179</p> <p>Richardson, J.E., Melosh, H.J., Greenberg, R., 2004. Impact-induced seismic activity on asteroid 433 Eros: a surface modification process. Science 306, 1526–1529. doi:10.1126/science.1104731</p> <p>Richardson, J.E., Melosh, H.J., Greenberg, R.J., O'Brien, D.P., 2005. The global effects of impact-induced seismic activity on fractured asteroid surface morphology. Icarus 179, 325–349. doi:10.1016/j.icarus.2005.07.005</p> <p>Richardson, J.E., Steckloff, J.K., Minton, D.A., 2020. Impact-produced seismic shaking and regolith growth on asteroids 433 Eros, 2867 Šteins, and 25143 Itokawa. Icarus 347, 113811. doi:10.1016/j.icarus.2020.113811</p>