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We report on the ephemeris development for Menoetius, the satellite of Patroclus. Our data set consisted of ground–based and Hubble Space Telescope relative astrometry, as well as 42 lightcurves from the mutual events seasons in 2007, 2012, and 2017/2018. Our dynamical model included the effects of oblate, nonspherical shapes of the components, and we assumed that Menoetius contained ∼22% of the system’s mass. We numerically integrated the equations of motion and obtained a set of dynamical parameters that fit the data. We report the fit results in terms of residuals, state vectors, orbital elements and their 1 σ uncertainties. The mean osculating semimajor axis is a = 692.5 ± 4.0 km, the mean eccentricity is e = 0.004 ± 0.004, and the International Celestial Reference Frame pole direction in R.A. and decl. is R. A. = 178.0 ± 0.5 deg, δ = −74.1 ± 0.2 deg. We determined the siderial orbital period of P = 4.282753 ± 0.000023 days. The fit yielded the system GM = 0.0950 ± 0.0012 km ^3 s ^−2 , which, in combination with the system volume determined from the stellar occultation and the assumed volume uncertainty of 20%, suggests a system bulk density of 1.05 ± 0.21 g cm ^−3 (1 σ ). The next season of mutual events starts in February of 2024 and lasts until January of 2025. The Patroclus system is in opposition for the observers on Earth in late September and is suitable for observations of the mutual events with an edge-on geometry in October.

We report on ephemerides for the satellites of Pluto based on the large set of astrometric measurements. Our orbit fit yielded the following masses with 1 σ uncertainties: GM _Pluto = 869.3 ± 0.4 km ^3 s ^−2 , GM _Charon = 106.1 ± 0.3 km ^3 s ^−2 , GM _Nix = 1.50 ± 0.52 × 10 ^−3 km ^3 s ^−2 , GM _Hydra = 2.01 ± 0.27 × 10 ^−3 km ^3 s ^−2 , corresponding to the densities of ρ _Pluto = 1.853 ± 0.004 g cm ^−3 , ρ _Charon = 1.705 ± 0.006 g cm ^−3 , ρ _Nix = 0.88 ± 0.31 g cm ^−3 , and ρ _Hydra = 1.21 ± 0.19 g cm ^−3 . Masses of Kerberos and Styx remain unconstrained, and it is unlikely that we will be able to measure them even if we obtain abundant 1 mas precision astrometry during the next 20 yr. We summarize the results of orbit integration in terms of osculating and precessing ellipse model mean elements. All satellites reside in near-circular orbits, and Kerberos and Styx have 0.4 deg and 0.3 deg inclinations with respect to Charon’s orbit plane. The nodal regression periods for Kerberos and Hydra are ∼9 and ∼14 yr respectively. We found that Charon’s orbit pole can be approximated as: R.A. = 133.0073 + 0.0036 T deg, and decl. = –6.2449 + 2.5 × 10 ^−5 T deg, where T is Julian centuries from the epoch J2000, based on 5000 yr of orbit integration.

We report radar, photometric, and visible-wavelength spectrophotometry observations of NEA 2018 EB obtained in 2018. The radar campaign started at Goldstone (8560 MHz, 3.5 cm) on April 7, and it was followed by more extensive observations from October 5 to 9 by both Arecibo (2380 MHz, 12.6 cm) and Goldstone. 2018 EB was observed optically on April 5, 8, and 9 and again on October 18. Spectrophotometry was obtained on October 19 with the SOAR telescope, and the data suggest that 2018 EB is an Xk-class object. The echo power spectra and delay-Doppler radar images revealed that 2018 EB is a binary system. Radar images constrained the satellite's diameter to ${0.15}_{-0.05}^{+0.02}$ km, but the data were not sufficient for shape modeling. Shape modeling of lightcurves and radar data yielded an oblate primary with an effective diameter D = 0.30 ± 0.04 km and a sidereal rotation period of ${4.3}_{-0.5}^{+0.6}$ hr. Measurements of delay-Doppler separations between the centers of mass of the primary and the satellite, along with the timing of a radar eclipse observed on October 9, resulted in an orbit fit for the satellite with a semimajor axis of ${0.50}_{-0.01}^{+0.04}$ km, an eccentricity of 0.15 ± 0.04, a period of ${16.85}_{-0.26}^{+0.33}$ hr, and an orbit pole constrained to the ecliptic longitudes and latitudes of $\lambda ={93}_{-{43}^{^\circ }}^{+{27}^{^\circ }}$ and $\beta ={48}_{-{18}^{^\circ }}^{+{7}^{^\circ }}$ . The system mass was estimated to be ${2.03}_{-0.08}^{+0.52}\times {10}^{10}$ kg, which yielded a bulk density of ${1.4}_{-0.5}^{+0.6}$ g cm ^−3 . Our analysis suggests that 2018 EB has a low optical albedo of p _V = 0.028 ± 0.016 and a relatively high radar albedo of η _OC = 0.29 ± 0.11 at Arecibo and η = 0.22 ± 0.10 at Goldstone.

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 ± 11 m and 290 ± 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by −2.63 ± 0.06 mm s ^−1 . Initially, after the impact, Dimorphos’s orbital period had changed by −32.7 minutes ± 16 s to 11.377 ± 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 ± 15 s, eventually stabilizing at 11.3674 ± 0.0004 hr. The total change in the orbital period was −33.25 minutes ±1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 ± 0.°2 day ^−1 . Under our model, this rate is driven by the oblateness parameter of Didymos, J _2 , as well as the spherical harmonics coefficients, C _20 and C _22 , of Dimorphos’s gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C _20 and C _22 estimates imply axial ratios, a / b and a / c , of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos’s shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.

We present the results of a fourth planetary defense exercise, focused this time on the small near-Earth asteroid (NEA) 2023 DZ2 and conducted during its close approach to the Earth in 2023 March. The International Asteroid Warning Network (IAWN), with support from NASA's Planetary Defense Coordination Office (PDCO), has been coordinating planetary defense observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. The last campaign focused on the NEA Apophis, and an outcome of that exercise was the need for a short burst campaign to replicate a real-life near-Earth object impact hazard scenario. The goal of the 2023 DZ2 campaign was to characterize the small NEA as a potential impactor and exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication with a short notice of just 24 hr. The entire campaign lasted about 10 days. The campaign team was divided into several working groups based on the characterization method: photometry, spectroscopy, thermal IR photometry and optical polarimetry, radar, and risk assessment. Science results from the campaign show that 2023 DZ2 has a rotation period of 6.2745 ± 0.0030 minutes; visible wavelength color photometry/spectroscopy/polarimetry and near-IR spectroscopy all point to an E-type taxonomic classification with surface composition analogous to aubrite meteorites; and radar observations show that the object has a diameter of 30 ± 10 m, consistent with the high albedo (0.49) derived from polarimetric and thermal IR observations.

We have conducted extremely ultradeep pencil-beam observations for new satellites around both Uranus and Neptune. Tens of images on several different nights in 2021, 2022, and 2023 were obtained, shifted, and added together to reach as faint as 26.9 and 27.2 mag in the r band around Uranus and Neptune, respectively. One new moon of Uranus, S/2023 U1, and two new moons of Neptune, S/2021 N1 and S/2002 N5, were found. S/2023 U1 was 26.6 mag, is about 7 km in diameter, and has a distant, eccentric, and inclined retrograde orbit similar to Caliban and Stephano, implying these satellites are fragments from a once larger parent satellite. S/2021 N1 was 26.9 mag, about 14 km in size, and has a retrograde orbit similar to Neso and Psamathe, indicating they are a dynamical family. We find S/2021 N1 is in Kozai–Lidov orbital resonance. S/2002 N5 was 25.9 mag, is about 23 km in size, and it makes a family of distant prograde satellites with Sao and Laomedeia. This survey mostly completes the outer satellites of Uranus to about 8 km and Neptune to about 14 km in diameter. The size distributions of satellite dynamical families around the giant planets shows a strong steepening in the power-law size distribution smaller than 5 km in diameter. The satellites of a family become much more common at diameters smaller than 5 km and their size distribution is consistent with a collisional breakup of a once larger parent satellite.