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On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG _1 G _2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

From the first phase of the high-cadence Formation of the Outer Solar System: an Icy Legacy (FOSSIL) survey, we analyzed lightcurves, ranging from one to four nights in length, of 371 trans-Neptunian objects (TNOs) for periodicity. We found 29 TNOs with periodic lightcurves, one of which is a good candidate for a close/contact binary. Another of the periodic FOSSIL TNOs could potentially have the fastest of all known TNO spin rates, with a period of 1.3 hr. We do not have total confidence in the period and thus plan to obtain a more detailed lightcurve for confirmation. The periodic TNOs have an average rotation period of 11.2 hr, close to the value obtained by Alexandersen et al., which had similar cadence, but different from other surveys. In regards to contention in the literature about whether smaller TNOs are more irregular in shape and thus have larger lightcurve amplitudes, we found that there is a weak correlation between absolute magnitude and lightcurve amplitude in a subset of 194 FOSSIL TNOs, even when using the more appropriate brightest (minimum) absolute magnitude instead of the time-averaged value.

PolCam, a wide-angle polarimetric camera, will be onboard the Korea Pathfinder Lunar Orbiter to investigate the lunar surface based on polarimetry. PolCam will construct a global lunar map of polarimetric parameters, such as maximal polarization (Pmax) and titanium distribution using three color bands centered at 320, 430, and 750 nm. PolCam's twin cameras are mounted at 45° tilt angles from the nadir across the orbital track in opposite directions. PolCam will obtain polarimetric measurements of sunlight scattered by the lunar surface at various phase angles up to ∼140° to achieve the scientific goals during the one-year mission. Since degree of linear polarization is a function of phase angle, it is essential to perform several measurements at various phase angles to properly retrieve, e.g., Pmax, Pmin, and the inversion angle, αinv. In this work, we show PolCam's phase-angle coverage as a function of selenographic longitudes from the equator to latitudes up to 70°N. Decreasing tilt angle to 25° and 0° limits the high end of phase-angle coverage, as well as the observational chances at high latitudes. [ABSTRACT FROM AUTHOR]

Polarimetry of the Moon reveals characteristics of the lunar regolith such as the size and composition of regolith grains, which are useful in understanding the surface properties and to determine landing sites for future lunar missions. As part of the Korea Pathfinder Lunar Orbiter (KPLO) mission, the wide-angle polarimetric camera (PolCam) will perform polarimetric measurements of the Moon for the first time from the lunar orbit. Because the degree of linear polarization is a function of the phase angle, it is necessary to observe the same region multiple times at various phase angles to construct the phase curve of polarization and derive the map of maximum polarization (Pmax). Any unexpected discontinuities of observing runs or an abrupt termination of the mission may cause the scientific goals of the PolCam to be unachievable. Here, we investigated how to recover the polarimetric phase curve when the observational data set is incomplete. Using ground-based polarimetry data, we explored the parameter space of the fitting formula of the phase curve and show that the formula can be reduced into a single parameter form. Assuming several cases of incomplete measurements, we constructed Pmax maps and investigated the allowable range of the phase-angle coverage. We show that Pmax can be estimated with a root-mean-square discrepancy less than 0.5%p when the maximum phase angle covered is greater than 90°. [ABSTRACT FROM AUTHOR]

To understand grain size evolution on the lunar surface in detail, we analyze the distribution of the average grain size for the lunar near side obtained by Jeong et al. Furthermore, we analyze the polarimetric properties of the regolith simulants SiC and JSC-1A in a laboratory. We find two characteristics of grain size evolution on the Moon. First, the lunar regolith has evolved on a specific evolutionary pathway in space. Here, Φ is defined as the ratio of the perpendicular () and parallel () components of the reflectance. Second, we also find that the evolutionary pathway depends on the FeO abundance and selenographic latitude of the surface. The dependence on the FeO content seems to result from the different resistance to comminution of regolith materials, and the dependence on the latitude seems to result from differences in the resurfacing environment. We present the probable causes of these characteristics of grain size evolution on the lunar surface. [ABSTRACT FROM AUTHOR]

We performed a monitoring observation of a Jupiter-family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using an aperture photometry package and derived the parameter, a proxy for the dust-production rate. We found that showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance of rh = 2.6–3.1 AU to a maximal value of 185 cm at rh = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at rh = 3.2 AU during the outbound orbit. We applied a model for characterizing dust-production rates as a function of rh and found that the fractional active area of the cometary nucleus had dropped from 20%–40% in 2008–2011 (around the aphelion) to 0.1%–0.3% in 2014–2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the Sun. Although a minor eruption was observed on UT 2015 January 26 at rh = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust (≲10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity. [ABSTRACT FROM AUTHOR]