We imaged Comet 252P/2000 G1 (LINEAR; hereafter 252P) with the Hubble Space Telescope and both 252P and P/2016 BA₁₄ (PanSTARRS; hereafter BA₁₄) with the Discovery Channel Telescope in 2016 March and April, surrounding its close encounter to Earth. The r′-band Afρ of 252P in a 0.″2-radius aperture were 16.8 ± 0.3 and 57 ± 1 cm on March 14 and April 4, respectively, and its gas production rates were Q(OH) = (5.8 ± 0.1) × 10²⁷ s⁻¹, and Q(CN) = (1.25 ± 0.01) × 10²⁵ s⁻¹ on April 17. The r′-band upper limit Afρ of BA₁₄ was 0.19 ± 0.01 cm in a 19.″2-radius aperture, and Q(CN) = (1.4 ± 0.1) × 10²² s⁻¹ on 2017 April 17. 252P shows a bright and narrow jet of a few hundred kilometers long in the sunward direction, changing its projected position angle in the sky with a periodicity consistent with 7.24 hr. However, its photometric light curve is consistent with a periodicity of 5.41 hr. We suggest that the nucleus of 252P is likely in a non-principal axis rotation. The nucleus radius of 252P is estimated to be about 0.3 ± 0.03 km, indicating an active fraction of 40% to >100% in its 2016 apparition. Evidence implies a possible cloud of slow-moving grains surrounding the nucleus. The activity level of 252P in the 2016 apparition increased by two orders of magnitude from its previous apparitions, making this apparition unusual. On the other hand, the activity level of BA₁₄ appears to be at least three orders of magnitude lower than that of 252P, despite its 10 times or larger surface area.

We investigate the phase angle dependence of asteroid light curves using numerical scattering models applied to simple body shapes. For simplicity, the Kaasalainen scattering parameters are obtained from the corresponding Hapke scattering laws for C-type, S-type, and V-type asteroids. The spectral types differ substantially in the role of multiple scattering (which is largely a function of their geometric albedos) but we find that the differences on the light curve versus phase relations are modest. Using a Kaasalainen scattering law, the amplitudes and axis ratios with respect to different phase angles from 0° to 140° are plotted for these types of asteroids based on a biaxial ellipsoid shape model. Additionally, we examine the relationship between amplitude and the axis ratio for a contact binary represented by identical biaxial ellipsoids, including the effects of shadowing of one component by the other. We compare the models with published high phase angle observations, and with interstellar object 1I/‘Oumuamua (Δm = 2.5 mag at a phase angle of α = 23°), finding an axis ratio of 5.2: 1 if represented as a single ellipsoid and 3.5: 1 for each component if represented as a nose-to-nose contact binary. While a detailed fit is not attempted, the comparison shows that the single ellipsoid model is better.

Binary asteroid exploration is an important research focus in the areas of deep space exploration and space informatics because of its unique scientific value in analyzing the structure and gravitational dynamic properties of asteroids, as well as the origin and evolution of celestial bodies in the solar system. Remote photometric observations can reveal the key characteristics of binary asteroids that differ from other kinds of asteroids, especially unary asteroids, and provide an efficient and convenient way to discover binary asteroids. However, the automatic binary asteroid detection problem by advanced machine learning methodology remains unresolved when handing complex asteroid photometric data. For this problem, this paper proposes to simulate unary and binary asteroid systems using cellinoid and oblate sphere shape models, and generate the corresponding light curve brightness information with different asteroid physical parameters. Then, a benchmark unary and binary asteroid light curve dataset is constructed. Afterward, a layered discriminative constrained energy minimization (LDCEM) method is developed to train a binary asteroid detector in a layered learning manner by enlarging the response differences between the light curve data of unary and binary asteroids, such that the two common kinds of asteroids can be well distinguished. The experimental results on the simulated asteroid light curve data, as well as the real observed asteroid light curve data, show that the proposed LDCEM method can yield promising binary asteroid detection performance in comparison with some representative detection methods.