On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We present here the results of an extensive, multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby. Our spectral data reveal no changes within systematic uncertainties. Post-flyby lightcurve photometry places strong constraints on the rotation state of Duende, showing that it is in non-principal axis rotation with fundamental periods of P-1 = 8.71 +/- 0.03 and P-2 = 23.7 +/- 0.2 h. Multiple lightcurve analysis techniques, coupled with theoretical considerations and delay-Doppler radar imaging, allow us to assign these periods to specific rotational axes of the body. In particular we suggest that Duende is now in a non-principal, short axis mode rotation state with a precessional period equal to P-1 and oscillation about the symmetry axis at a rate equal to P-2. Temporal and signal-to-noise limitations inherent to the pre-flyby photometric dataset make it difficult to definitively diagnose whether these periods represent a change imparted due to gravitational torques during the flyby. However, based on multiple analysis techniques and a number of plausibility arguments, we suggest that Duende experienced a rotational change during the planetary encounter with an increase in its precessional rotation period. Our preferred interpretation of the available data is that the precession rate increased from 8.4 h prior to the flyby to 8.7 h afterwards. A companion paper by Benson et al. (2019) provides a more detailed dynamical analysis of this event and compares the data to synthetic lightcurves computed from a simple shape model of Duende. The interpretation and results presented in these two works are consistent with one another. The ultimate outcome of this campaign suggests that the analytic tools we employed are sufficient to extract detailed information about solid-body rotation states given data of high enough quality and temporal sampling. As current and future discovery surveys find more near-Earth asteroids, the opportunities to monitor for physical changes during planetary encounters will increase.

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

We present the discovery that ASASSN-14ko is a periodically flaring active galactic nucleus at the center of the galaxy ESO 253-G003. At the time of its discovery by the All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a supernova close to the nucleus. The subsequent 6 yr of V- and g-band ASAS-SN observations revealed that ASASSN-14ko has nuclear flares occurring at regular intervals. The 17 observed outbursts show evidence of a decreasing period over time, with a mean period of P-0 = 114.2 0.4 days and a period derivative of P = -0.0017 +/- 0.003 . The most recent outburst in 2020 May, which took place as predicted, exhibited spectroscopic changes during the rise and had a UV bright, blackbody spectral energy distribution similar to tidal disruption events (TDEs). The X-ray flux decreased by a factor of 4 at the beginning of the outburst and then returned to its quiescent flux after similar to 8 days. The Transiting Exoplanet Survey Satellite observed an outburst during Sectors 4-6, revealing a rise time of 5.60 0.05 days in the optical and a decline that is best fit with an exponential model. We discuss several possible scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a repeated partial TDE. The next outbursts should peak in the optical on UT 2020 September 7.41.1 and UT 2020 December 26.51.4.

Trans-Neptunian Objects (TNOs) in the scattered disk with 50 less than or similar to a less than or similar to 100 au are thought to cluster near Neptune's n:1 resonances (e.g., 3:1, 4:1, and so on). While these objects spend lengthy periods of time at large heliocentric distances, if their perihelia remain less than around 40 au, their dynamical evolution is still largely coupled to Neptune's. Conversely, around a dozen extreme TNOs with a greater than or similar to 250 au and detached perihelia seem to exist in a regime where they are too distant to be affected by the giant planets and too close for their dynamics to be governed by external forces. Recent work suggests that the apparent alignment of these orbits in physical space is a signature of gravitational shepherding by a distant massive planet. In this paper, we investigate the evolution of TNOs in each of Neptune's n:1 resonances between the 3:1 and 14:1. We conclude that both resonant and nonresonant objects beyond the 12:1 near similar to 157 au are removed rather efficiently via perturbations from the hypothetical Planet Nine. Additionally, we uncover a population of simulated TNOs with a less than or similar to 100 au, 40 less than or similar to q less than or similar to 45 au, and low inclinations that experience episodes of resonant interactions with both Neptune and Planet Nine. Finally, we simulate the evolution of observed objects with a > 100 au and identify several TNOs that are potentially locked in n:1 resonances with Neptune, including the most distant known resonant candidates, 2014 JW(80) and 2014 OS394,which appear to be in the 10:1 and 11:1 resonances, respectively. Our results suggest that the detection of similar remote objects might provide a useful constraint on hypotheses invoking the existence of additional distant planets.

We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN(173) (also now designated Comet 433P), which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. From archival data analysis, we estimate g'-, r'-, i'-, and z'-band absolute magnitudes for the nucleus of H-g = 16.62 +/- 0.13, H-r = 16.12 +/- 0.10, H-i = 16.05 +/- 0.11, and H-z = 15.93 +/- 0.08, corresponding to nucleus colors of g' - r' = 0.50 +/- 0.16, r' - i' = 0.07 +/- 0.15, and i' - z' = 0.12 +/- 0.14; an equivalent V-band absolute magnitude of H-V = 16.32 +/- 0.08; and a nucleus radius of r(n) = 1.6 +/- 0.2 km (using a V-band albedo of pV = 0.054 +/- 0.012). Meanwhile, we find mean near-nucleus coma colors when 248370 is active of g' - r' = 0.47 +/- 0.03, r' - i' = 0.10 +/- 0.04, and i' - z' = 0.05 +/- 0.05 and similar mean dust tail colors, suggesting that no significant gas coma is present. We find approximate ratios between the scattering cross sections of near-nucleus dust (within 5000 km of the nucleus) and the nucleus of A(d)/A(n) = 0.7 +/- 0.3 on 2016 July 22 and 1.8 < A(d)/A(n) < 2.9 in 2021 July and August. During the 2021 observation period, the coma declined in intrinsic brightness by similar to 0.35 mag (or similar to 25%) in 37 days, while the surface brightness of the dust tail remained effectively constant over the same period. Constraints derived from the sunward extent of the coma and width of the tail as measured perpendicular to the orbit plane suggest that the terminal velocities of ejected dust grains are extremely slow (similar to 1 m s(-1) for 1 mu m particles), suggesting that the observed dust emission may be aided by rapid rotation of the nucleus lowering the effective escape velocity.

Precise densities of red dwarf exoplanets help distinguish potential "water worlds".

Time-dependent, or 4-D, microgravity changes observed at the Laguna del Maule volcanic field, Chile, since 2013, indicate significant (1.5 x 10(11) kg) ongoing mass injection. Mass injection is focused along the Troncoso fault, and subparallel structures beneath the lake at 1.5-2 km depth, and is best modeled by a vertical rectangular prism source. The low-density change (156 to 307 kg/m(3)) and limited depth extent suggest a mechanism of hydrothermal fluid intrusion into existing voids, or voids created by the substantial uplift, rather than deeper-sourced dike intrusion of rhyolite or basalt magma. Although the gravity changes are broadly spatially coincident with ongoing surface deformation, existing models that explain the deformation are deeper sourced and cannot explain the gravity changes. To account for this discrepancy and the correspondence in time of the deformation and gravity changes, we explore a coupled magmatectonic interaction mechanism that allows for shallow mass addition, facilitated by deeper magma injection. Computing the strain, and mean, normal, and Coulomb stress changes on northeast trending faults, caused by the opening of a sill at 5 km depth, shows an increase in strain and mean and normal stresses along these faults, coincident with the areas of mass addition. Seismic swarms in mid-2012 to the west and southwest of the mass intrusion area may be responsible for dynamically increasing permeability on the Troncoso fault, promoting influx of hydrothermal fluids, which in turn causes larger gravity changes in the 2013 to 2014 interval, compared to the subsequent intervals.

Large rhyolitic volcanoes pose a hazard, yet the processes and signals foretelling an eruption are obscure. Satellite geodesy has revealed surface inflation signaling unrest within magma reservoirs underlying a few rhyolitic volcanoes. Although seismic, electrical, and potential field methods may illuminate the current configuration and state of these reservoirs, they cannot fully address the processes by which they grow and evolve on geologic time scales. We combine measurement of a deformed paleoshore surface, isotopic dating of volcanism and surface exposure, and modeling to determine the rate of growth of a rhyolite-producing magma reservoir. The numerical approach builds on a magma intrusion model developed to explain the current, decade-long, surface inflation at >20 cm/year. Assuming that the observed 62-m uplift reflects several non-eruptive intrusions of magma, each similar to the unrest over the past decade, we find that similar to 13 km(3) of magma recharged the reservoir at a depth of similar to 7 km during the Holocene, accompanied by the eruption of similar to 9 km(3) of rhyolite. The long-term rate of magma input is consistent with reservoir freezing and pluton formation. Yet, the unique set of observations considered here implies that large reservoirs can be incubated and grow at shallow depth via episodic high-flux magma injections. These replenishment episodes likely drive rapid inflation, destabilize cooling systems, propel rhyolitic eruptions, and thus should be carefully monitored.

Extensive vertical deformation (>4.5 m) observed at Sierra Negra volcano Galapagos, Ecuador, between 1992 and the 2005 eruption led scientists to hypothesize that repeated faulting events relieved magma chamber overpressure and prevented eruption. To better understand the catalyst of the 2005 eruption, thermomechanical models are used to track the stress state and stability of the magma storage system during the 1992-2005 inflation events. Numerical experiments indicate that the host rock surrounding the Sierra Negra reservoir remained in compression with minimal changes in overpressure (similar to 10 MPa) leading up to the 2005 eruption. The lack of tensile failure and minimal overpressure accumulation likely inhibited dike initiation and accommodated the significant inflation without the need for pressure relief through shallow trapdoor faulting events. The models indicate that static stress transfer due to the M-w 5.4 earthquake 3 hr prior to the eruption most likely triggered tensile failure and catalyzed the 2005 eruption.