Near-Simultaneous Optical + NIR Photometry of Interstellar Comet 2I/Borisov

<p>In August 2019, 2I/Borisov, the second interstellar object and first visibly active interstellar comet, was discovered on a trajectory nearly perpendicular to the ecliptic. Observations of planet forming disks and debris disks serve as probes of the ensemble properties of extrasolar planetesimals, but the passage of an active interstellar comet through our Solar System provides a rare opportunity to individually study these small bodies up close in the same ways in which we investigate objects originating from our own Outer Solar System. Ground-based observations of short period comet <span>67P/Churyumov–Gerasimenko</span> revealed a coma dust composition indistinguishable from what was measured on its nucleus by the orbiting <em>Rosetta</em> spacecraft. Therefore when 2/I Borisov had a dust dominated tail, we attempted to study its composition with near-simultaneous griJ photometry with the Gemini North Telescope. We obtained two epochs of GMOS-N and NIRI observations in November 2019, separated by two weeks. We will report on the inferred optical-near-IR colors of 2I/I Borisov’s dust coma/tail and nucleus. We will compare our measurements to other observations of 2I/Borisov and place the interstellar comet in context with the Col-OSSOS (Colours of the Outer Solar System Survey) sample of small KBOs and interstellar object <span>ʻOumuamua</span> observed in grJ with Gemini North, using the same setup.</p>

Comparing the reflectivity of ungrouped carbonaceous chondrites with those of short-period comets like 2P/Encke

Aims. The existence of asteroid complexes produced by the disruption of these comets suggests that evolved comets could also produce high-strength materials able to survive as meteorites. We chose as an example comet 2P/Encke, one of the largest object of the so-called Taurid complex. We compare the reflectance spectrum of this comet with the laboratory spectra of some Antarctic ungrouped carbonaceous chondrites to investigate whether some of these meteorites could be associated with evolved comets. Methods. We compared the spectral behaviour of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different specimens of the common carbonaceous chondrite groups do not match the overall features and slope of the comet 2P/Encke. By testing anomalous carbonaceous chondrites, we found two meteorites: Meteorite Hills 01017 and Grosvenor Mountains 95551, which could be good proxies for the dark materials that formed this short-period comet. We hypothesise that these two meteorites could be rare surviving samples, either from the Taurid complex or another compositionally similar body. In any case, it is difficult to get rid of the effects of terrestrial weathering in these Antarctic finds, and further studies are needed. A future sample return from the so-called dormant comets could also be useful to establish a ground truth on the materials forming evolved short-period comets. Results. As a natural outcome, we think that identifying good proxies of 2P/Encke-forming materials might have interesting implications for future sample-return missions to evolved, potentially dormant, or extinct comets. Understanding the compositional nature of evolved comets is particularly relevant in the context of the future mitigation of impact hazard from these dark and dangerous projectiles.

Stability of Jovian Trojans and their collisional families

ABSTRACT The Jovian Trojans are two swarms of objects located around the L4 and L5 Lagrange points. The population is thought to have been captured by Jupiter during the Solar system’s youth. Within the swarms, six collisional families have been identified in previous work, with four in the L4 swarm, and two in the L5. Our aim is to investigate the stability of the two Trojan swarms, with a particular focus on these collisional families. We find that the members of Trojan swarms escape the population at a linear rate, with the primordial L4 (23.35 per cent escape) and L5 (24.89 per cent escape) population sizes likely 1.31 and 1.35 times larger than today. Given that the escape rates were approximately equal between the two Trojan swarms, our results do not explain the observed asymmetry between the two groups, suggesting that the numerical differences are primordial in nature, supporting previous studies. Upon leaving the Trojan population, the escaped objects move on to orbits that resemble those of the Centaur and short-period comet populations. Within the Trojan collisional families, the 1996 RJ and 2001 UV209 families are found to be dynamically stable over the lifetime of the Solar system, whilst the Hektor, Arkesilos and Ennomos families exhibit various degrees of instability. The larger Eurybates family shows 18.81 per cent of simulated members escaping the Trojan population. Unlike the L4 swarm, the escape rate from the Eurybates family is found to increase as a function of time, allowing an age estimation of approximately 1.045 ± 0.364 × 109 yr.

Meteoroid-stream complex originating from comet 2P/Encke

Aims. We present a study of the meteor complex of the short-period comet 2P/Encke. Methods. For five perihelion passages of the parent comet in the past, we modeled the associated theoretical stream. Specifically, each of our models corresponds to a part of the stream characterized with a single value of the evolutionary time and a single value of the strength of the Poynting–Robertson effect. In each model, we follow the dynamical evolution of 10 000 test particles via a numerical integration. The integration was performed from the time when the set of test particles was assumed to be ejected from the comet’s nucleus up to the present. At the end of the integration, we analyzed the mean orbital characteristics of those particles that approached the Earth’s orbit, and thus created a meteor shower or showers. Using the mean characteristics of the predicted shower, we attempted to select its real counterpart from each of five considered databases (one photographic, three video, and one radio-meteor). If at least one attempt was successful, the quality of the prediction was evaluated. Results. The modeled stream of 2P approaches the Earth’s orbit in several filaments with the radiant areas grouped in four cardinal directions of ecliptical showers. These groups of radiant areas are situated symmetrically with respect to the apex of the Earth’s motion around the Sun. Specifically, we found that showers #2, #17, #156, #172, #173, #215, #485, #624, #626, #628, #629, #632, #634, #635, #636, and #726 in the IAU-MDC list of all showers are dynamically related to 2P. In addition, we found five new 2P-related showers in the meteor databases considered.

Spectrophotometrical researches of the subnuclear area of 46P/WIRTANEN comet

The observations and research of the short-period comet 46P/Wirtanen by optical spectra with an average resolution (λ/Δλ ≈ 1400) are presented. Spectra in January 2008 at the Peak Terskol mountain observatory with the Zeiss-2000 telescope (D = 2.0 m; F2 = 16 m) were obtained. On the basis of the received spectral material, the identification of emission bands was carried out. The distribution of the total energy flux, reflected energy flux and the spectrophotometric gradient in the spectral range λλ = 4850–7650 ÅÅ are constructed. The quality of the received spectral material allowed estimating with high accuracy the gas productivity of the molecules C2, NH2 and the relative dust productivity in cometary filters GC, RC. The relative dust productivity (Afρ), the gas productivity (Q) for the molecular emissions of C2 and NH2, as well as some other physical parameters of the neutral gas cometary atmosphere were evaluated. The resulting values of physical quantities are characteristic for Jupiter family comets. The gas productivity of 46P/Wirtanen during the observation period QC2 = 3.97–4.12 × 1025 mol/s, QNH2 = 2.06–2.97 × 1025 mol/s. The obtained values of gas and dust productivity characterize the cometary coma of 46P/Wirtanen as dust-rich. In comparison with the data of 1998, a significant decrease in production in the atmosphere of the comet of the NH2 molecule was recorded. The spectrophotometric gradient obtained for comet Wirtanen is characteristic for other JFC and is 8.6 % per 1000 Å. The relative dust productivity (Afρ) at the time of observations in January 2008 was significantly higher than in previous passages of perihelion. The obtained results may be the consequence of evolution of the upper layers of the cometary nucleus and require further experimental confirmation.