The Main Belt Comet 133P/Elst-Pizarro is one of the targets of the proposed Chinese small body exploration mission. The rotation and gravity of this comet will be modeled at the end of the mission phase. To prepare this mission, we performed a radio science simulation based on the current knowledge of the characteristics of 133P/Elst-Pizarro. Simulated two-way Earth-orbiter and orbiter-lander range rate tracking data with a lander positioned at the comet equator were used to determine the gravity field coefficients and the rotational parameters. Our simulation results show that the introduction of the orbiter-lander range rate data can significantly decrease the uncertainty in the initial state vector of the orbiter as well as the uncertainty in the rotation and gravity parameters.

In China’s asteroid mission to be launched around 2025, (7968) 133P/Elst-Pizarro (hereafter 133P) will be the second target, after a visit to asteroid (469219) Kamo’oalewa. This paper describes a simulation of precise orbit determination for the spacecraft around comet 133P, as well as estimation of its gravitational parameter (GM) value and the solar radiation pressure coefficient Cr for the spacecraft. Different cometocentric distances of 200, 150 and 100 km orbits are considered, as well as two tracking modes: exclusive two-way range-rate mode (Earth station to spacecraft) and combinations of two-way range-rate and local spacecraft onboard ranging to the comet. Compared to exclusive two-way range-rate, the introduction of local ranging observables improves the final GM uncertainties by up to one order of magnitude. An ephemeris error in the orbit of 133P is also considered, and we show that, to obtain a reliable estimate of the GM for 133P, this error cannot exceed a one km range.

Context. The cryptomare in the Balmer-Kapteyn region is the oldest one on the Moon. Determining the extent and formation of this feature can deepen our understanding of early mare volcanism and help establish temporal and spatial constraints on lunar thermal and volcanic history. Aims. This paper focuses on the identification of lunar cryptomaria and figuring out their formation processes. Methods. We used the Global WAC digital terrain model to analyze the terrain. We built a mathematical model using support vector machines and input Kaguya Multiband Imager data to estimate oxide concentrations in the Balmer-Kapteyn region. We used the Chandrayaan-1 Moon Mineralogy Mapper (M3) to analyze the minerals. We improved the cryptomare identification model to increase the accuracy of basalt identification in the cryptomare region. Finally, we used three methods to estimate the ejecta thickness of the target basin to the Balmer-Kapteyn region. Results. New Al2O3, CaO, FeO, MgO, and TiO2 maps were generated using the Kaguya Multiband Imager and a novel machine-learning model. As a result, the extent of the cryptomare in the Balmer-Kapteyn region was redefined and the formation process of the cryptomare in the Balmer-Kapteyn region was divided into five formation stages: Balmer basin formation, ejecta coverage from the Pre-Nectarian and Nectarian large impact basins, mare basalt filling, ejecta secondary coverage of high-albedo materials, and exposure of mare basalts. Conclusions. We found that the bottom of the Crater Vendelinus is likely to hide ancient mare basalt. Moreover, the high-aluminum mare basalt of the cryptomare is different from the composition of the exposed mare basalts in Mare Fecunditatis and Crater Vendelinus. The high-albedo material covering the cryptomare in the Balmer-Kapteyn region could have come from the Langrenus, Petavius, Humboldt, La Perouse, and Ansgarius Craters, along with some from the Orientale Basin impact event or potentially from the Imbrium Basin impact event.