Size and Albedo Constraints for (152830) Dinkinesh Using WISE Data

Probing small main-belt asteroids provides insight into their formation and evolution through multiple dynamical and collisional processes. These asteroids also overlap in size with the potentially hazardous near-earth object population and supply the majority of these objects. The Lucy mission will provide an opportunity for study of a small main-belt asteroid, (152830) Dinkinesh. The spacecraft will perform a flyby of this object on November 1, 2023, in preparation for its mission to the Jupiter Trojan asteroids. We employed aperture photometry on stacked frames of Dinkinesh obtained by the Wide-field-Infrared Survey Explorer and performed thermal modeling on a detection at 12 $\mu$m to compute diameter and albedo values. Through this method, we determined Dinkinesh has an effective spherical diameter of $0.76^{+0.11}_{-0.21}$ km and a visual geometric albedo of $0.27^{+0.25}_{-0.06}$ at the 16th and 84th percentiles. This albedo is consistent with typical stony (S-type) asteroids.Comment: Submitted to Astrophysical Journal Letter

Thermal evolution and activity of Comet 9P/Tempel 1 and simulation of a deep impact

We use a quasi 3-D thermal evolution model for a spherical comet nucleus, which takes into account the diurnal and latitudinal variation of the solar flux, but neglects lateral heat conduction. We model the thermal evolution and activity of Comet 9P/Tempel 1, in anticipation of the Deep Impact mission encounter with the comet. We also investigate the possible outcome of a projectile impact, assuming that all the energy is absorbed as thermal energy. An interesting result of this investigation, is that the estimated amount of dust ejected due to the impact is equivalent to 2--2.6 days of activity, during "quiet" conditions, at perihelion. We show that production rates of volatiles that are released in the interior of the nucleus depend strongly on the porous structure, in particular on the surface to volume ratio of the pores. We develop a more accurate model for calculating this parameter, based on a distribution of pore sizes, rather than a single, average pore size.Comment: 25 pages, 8 figures, accepted for publication in PASP (in press). For fig.xx (composite image, sec.4) and a better resolution of fig.6 see, http://geophysics.tau.ac.il/personal/gal%5Fsarid

Ground-based Optical and SPITZER Infrared Imaging Observations of Comet 21P/Giacobini-Zinner

We present ground-based optical and Spitzer Space Telescope infrared imaging observations of the ecliptic (Jupiter-family) comet 21P/Giacobini-Zinner, the parent body of the Draconid meteor stream, during its 2005 apparition. Onset of nucleus activity occurred at a pre-perihelion heliocentric distance, < 3.80 AU, while post-perihelion 21P was dusty (peak Afrho = 131 cm^{-1}) and active out to heliocentric distances > 3.3 AU following a logarithmic slope with heliocentric distance -2.04. Coma colors, (V-R) = 0.524 +/- 0.003, (R-I) = 0.487 +/- 0.004 are redder than solar, yet comparable to colors derived for other Jupiter-family comets. A nucleus radius of 1.82 +/- 0.05 km is derived from photometry at quiescence. Spitzer images post-perihelion exhibit an extensive coma with a prominent dust tail, where excess emission (over the dust continuum) in the 4.5 micron IRAC image arises from volatile gaseous CO and/or CO2. No dust trail was detected (3-sigma surface brightness upper-limit of 0.3 MJy/sr/pixel) along the projected velocity vector of comet 21P in the MIPS 24 micron image suggesting that the number density of trail particles is < 7 x 10^{-11} m^{-3}. The bolometric albedo of 21P derived from the contemporaneous optical and Spitzer observations is A(theta = 22 degr.) = 0.11, slightly lower than values derived for other comets at the same phase angle.Comment: Astronomical Journal Accepted, 20 pages text and references, 3 tables, and 8 figure

Observational and Dynamical Characterization of Main-Belt Comet P/2010 R2 (La Sagra)

We present observations of comet-like main-belt object P/2010 R2 (La Sagra) obtained by Pan-STARRS 1 and the Faulkes Telescope-North on Haleakala in Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea, the Danish 1.54 m telescope at La Silla, and the Isaac Newton Telescope on La Palma. An antisolar dust tail is observed from August 2010 through February 2011, while a dust trail aligned with the object's orbit plane is also observed from December 2010 through August 2011. Assuming typical phase darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag between August 2010 and December 2010, suggesting that dust production is ongoing over this period. These results strongly suggest that the observed activity is cometary in nature (i.e., driven by the sublimation of volatile material), and that P/La Sagra is therefore the most recent main-belt comet to be discovered. We find an approximate absolute magnitude for the nucleus of H_R=17.9+/-0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an albedo of p=0.05. Using optical spectroscopy, we find no evidence of sublimation products (i.e., gas emission), finding an upper limit CN production rate of Q_CN<6x10^23 mol/s, from which we infer an H2O production rate of Q_H2O<10^26 mol/s. Numerical simulations indicate that P/La Sagra is dynamically stable for >100 Myr, suggesting that it is likely native to its current location and that its composition is likely representative of other objects in the same region of the main belt, though the relatively close proximity of the 13:6 mean-motion resonance with Jupiter and the (3,-2,-1) three-body mean-motion resonance with Jupiter and Saturn mean that dynamical instability on larger timescales cannot be ruled out.Comment: 23 pages, 13 figures, accepted for publication in A

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day−1 in the first week, and 0.08–0.09 mag day−1 over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role

Dust Evolution Of Comet 9P/Tempel 1

We present wide-field g, r, and i-band images of comet 9P/Tempel 1, target of the Deep Impact mission, taken with the MegaCam CCD (FOV 1° × 1°) on the 3.6-m Canada-France-Hawaii Telescope on Mauna Kea. Our observations on UT July 3-6, 2005, covered the night prior to impact to ensure that we have data for the pre-impact dust environment. The two nights following impact allowed us to monitor the inner coma for changes in grain size properties as a result of the impact. We created a deep composite image (from three hours of observing time) for each night. Our morphological studies can establish the pattern of dust emission from the nucleus, which is determined by the surface distribution of discrete sources of dust on the rotating nucleus and their temporal evolution. The scientific questions we address are: How does post-impact dust differ from pre-impact dust? Is there any compositional difference between surface and subsurface grains? Does surface mantling change this? From the relative photometry we observed that some of the impact ejecta leaves our smallest aperture within the first hour after the impact. The light curves through different apertures implies that the ejecta was traveling roughly 200 ms-1 projected on the sky. Fifty hours after the impact, the core of the comet was within a few tenths of a magnitude back to its pre-impact brightness. Also by our last night the morphology of the coma had begun to return to its pre-impact shape. © 2009 Springer-Verlag Berlin Heidelberg

Stardust-Next, Deep Impact, And The Accelerating Spin Of 9P/Tempel 1

The evolution of the spin rate of Comet 9P/Tempel 1 through two perihelion passages (in 2000 and 2005) is determined from 1922 Earth-based observations taken over a period of 13. year as part of a World-Wide observing campaign and from 2888 observations taken over a period of 50 days from the Deep Impact spacecraft. We determine the following sidereal spin rates (periods): 209.023 ± 0.025°/dy (41.335 ± 0.005. h) prior to the 2000 perihelion passage, 210.448 ± 0.016°/dy (41.055 ± 0.003. h) for the interval between the 2000 and 2005 perihelion passages, 211.856 ± 0.030°/dy (40.783 ± 0.006. h) from Deep Impact photometry just prior to the 2005 perihelion passage, and 211.625 ± 0.012°/dy (40.827 ± 0.002. h) in the interval 2006-2010 following the 2005 perihelion passage. The period decreased by 16.8 ± 0.3. min during the 2000 passage and by 13.7 ± 0.2. min during the 2005 passage suggesting a secular decrease in the net torque. The change in spin rate is asymmetric with respect to perihelion with the maximum net torque being applied on approach to perihelion. The Deep Impact data alone show that the spin rate was increasing at a rate of 0.024 ± 0.003°/dy/dy at JD2453530.60510 (i.e., 25.134 dy before impact), which provides independent confirmation of the change seen in the Earth-based observations.The rotational phase of the nucleus at times before and after each perihelion and at the Deep Impact encounter is estimated based on the Thomas et al. (Thomas et al. [2007]. Icarus 187, 4-15) pole and longitude system. The possibility of a 180° error in the rotational phase is assessed and found to be significant. Analytical and physical modeling of the behavior of the spin rate through of each perihelion is presented and used as a basis to predict the rotational state of the nucleus at the time of the nominal (i.e., prior to February 2010) Stardust-NExT encounter on 2011 February 14 at 20:42.We find that a net torque in the range of 0.3-2.5×107kgm2s-2 acts on the nucleus during perihelion passage. The spin rate initially slows down on approach to perihelion and then passes through a minimum. It then accelerates rapidly as it passes through perihelion eventually reaching a maximum post-perihelion. It then decreases to a stable value as the nucleus moves away from the Sun. We find that the pole direction is unlikely to precess by more than ~1° per perihelion passage. The trend of the period with time and the fact that the modeled peak torque occurs before perihelion are in agreement with published accounts of trends in water production rate and suggests that widespread H2O out-gassing from the surface is largely responsible for the observed spin-up. © 2011 Elsevier Inc

Observational Characterization of Main-belt Comet and Candidate Main-belt Comet Nuclei

We report observations of nine main-belt comets (MBCs) or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of p _V = 0.05 ± 0.02) of r _n = (0.24 ± 0.05) km for 238P/Read, r _n = (0.9 ± 0.2) km for 313P/Gibbs, r _n = (0.6 ± 0.1) km for 324P/La Sagra, r _n = (1.0 ± 0.2) km for 426P/PANSTARRS, r _n = (0.5 ± 0.1) km for 427P/ATLAS, r _n 80% have r _n ≤ 1.0 km, pointing to an apparent physical preference toward small MBCs, where we suggest that Yarkovsky–O’Keefe–Radzievskii–Paddack spin-up may play a significant role in triggering and/or facilitating MBC activity

Physical Characterization of Main-belt Comet (248370) 2005 QN₁₇₃

We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN173 (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 $g^{\prime}$-, $r^{\prime}$-, $i^{\prime}$-, and $z^{\prime}$-band absolute magnitudes for the nucleus of Hg = 16.62 ± 0.13, Hr = 16.12 ± 0.10, Hi = 16.05 ± 0.11, and Hz = 15.93 ± 0.08, corresponding to nucleus colors of $g^{\prime} -r^{\prime} =0.50\pm 0.16$, $r^{\prime} -i^{\prime} =0.07\pm 0.15$, and $i^{\prime} -z^{\prime} =0.12\pm 0.14$; an equivalent V-band absolute magnitude of HV = 16.32 ± 0.08; and a nucleus radius of rn = 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 $g^{\prime} -r^{\prime} =0.47\pm 0.03$, $r^{\prime} -i^{\prime} =0.10\pm 0.04$, and $i^{\prime} -z^{\prime} =0.05\pm 0.05$ 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 Ad/An = 0.7 ± 0.3 on 2016 July 22 and 1.8 < Ad/An < 2.9 in 2021 July and August. During the 2021 observation period, the coma declined in intrinsic brightness by ∼0.35 mag (or ∼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 (∼1 m s−1 for 1 μm particles), suggesting that the observed dust emission may be aided by rapid rotation of the nucleus lowering the effective escape velocity