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 ′ -, 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 p V = 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 ∼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.

The dust and gas environment of comet 8P/Tuttle

ABSTRACT Comet 8P/Tuttle has been selected as a possible backup target for the Comet Interceptor mission (ESA). This comet was observed intensively during its previous perihelion passage, in 2008 January. From those observations, important information was obtained about the physical properties of the nucleus and coma. This study focuses on the coma of 8P/Tuttle using visible spectra and images to derive gas and dust production rates. The production rates obtained suggest that this comet can be considered as ‘typical’ concerning the C2/CN and C3/CN ratios, although, depending on the criteria adopted, it could be defined as C3 depleted. NH2 production rates suggest an enrichment of this molecule. Visible and infrared images have been analysed using a Monte Carlo dust tail model. At comparatively large heliocentric distances, the coma is characterized by a dust-to-water ratio around or less than 1. Nevertheless, when the comet approaches perihelion, and the subsolar latitude crosses the equator, the coma dust-to-water ratio increases significantly, reaching values larger than six. Such a high dust-to-gas ratio around perihelion suggests that the nucleus of 8P/Tuttle is also ‘typical’ regarding the refractory content, considering the comparatively high values of that magnitude estimated for different comets.

The dust tail gap of C/2014 Q1 (PanSTARRS)

&lt;p&gt;A dust tail &amp;#8216;gap&amp;#8217; was discovered in amateur images of the dust tail of C/2014 Q1 (PanSTARRS), which appeared around the comet&amp;#8217;s most recent perihelion on 6&lt;sup&gt;th&lt;/sup&gt; July 2015. This gap presented itself as a wedge-shaped region devoid of dust, with the comet&amp;#8217;s dust tail appearing to be normal on either side of this dark zone.&lt;/p&gt; &lt;p&gt;The results of the C/2014 Q1 study, employing Finson-Probstein modelling of the dust tail, show that none of the dust lay along the comet&amp;#8217;s orbital path, confirming that both sections of dust were part of the dust tail and not a typical separation between dust tail and dust trail. A gap, devoid of dust, separates these two sections. The edges of this gap are bounded fairly accurately by lines of constant dust ejection time, corresponding to dust that should have been ejected between 6&lt;sup&gt;th&lt;/sup&gt; July and 12&lt;sup&gt;th&lt;/sup&gt; July. This suggests that cometary activity between these two dates was drastically reduced, although the cause of this is still unknown. The gap was visible throughout July and August 2015, and its shape and structure remained constant in the context of expected dust tail behaviour. &amp;#160;&lt;/p&gt; &lt;p&gt;The limited dataset for C/2014 Q1 meant that the formation mechanism of this gap could not be fully investigated. &amp;#160;However,&amp;#160;a&amp;#160;subsequent&amp;#160;survey of&amp;#160;amateur and professional comet&amp;#160;images revealed the presence of similar&amp;#160;gaps in the dust tails of several&amp;#160;other&amp;#160;comets. Analysis of these comets show many similarities with the results of the C/2014 Q1 study, including that these dust gaps observed all form during the comets&amp;#8217; perihelia. We present the results of individual analyses&amp;#160;and&amp;#160;cross-comparison of these&amp;#160;comets, and&amp;#160;summarize what we believe are the most likely scenarios for the formation of these perplexing features.&amp;#160;&lt;/p&gt;

Comet Dust Tail Analysis using the Finson-Probstein Model

&lt;p&gt;The fine-structure detail of several comet dust tails is analysed from amateur and professional comet images using the Finson-Probstein mdoel. Given the date and time of the image taken, the comet&amp;#8217;s position in the sky is calculated using an open source algorithm [1] and the comet&amp;#8217;s dust tail is simulated for that position and time. This modeled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image to a dust grain beta against ejection time plot [2], tail structures can be more easily identified and analysed. This also allows for the tracking of tail structure over time, as images of a single comet from different times and observatories can be mapped onto the same plot. This method compensates for the difficulties of investigating tail structures in images as the comet moves across the image and as viewing geometry changes over time. &amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt; &lt;p&gt;This is a continuation of the work done previously on Comet C/2006 P1 (McNaught), which ultimately led to the observation of the formation processes of new fine-scale structure features in the comet&amp;#8217;s dust tail [2]. This model is now applied to several other comets, including the recent Comet ATLAS (C/2019 Y4), to map their tail structures and to highlight this model&amp;#8217;s utility in comet dust tail analysis.&lt;/p&gt; &lt;p&gt;Finally, this work will be put into context as the first step in the development of an automated analysis method for cometary dust and ion tails. This automated method is in preparation for the upcoming opening of the Vera Rubin Observatory (LSST), and aims to automatically identify comet tail structures from the Observatory&amp;#8217;s stream of comet images. The robustness of this analysis suite enables it to also be implemented on amateur comet images, making use of the abundant and valuable data from amateur astronomers.&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;[1] Lang, Dustin, David W. Hogg, Keir Mierle, Michael Blanton, and Sam Roweis. 2010. &quot;ASTROMETRY.NET: BLIND ASTROMETRIC CALIBRATION OF ARBITRARY ASTRONOMICAL IMAGES&quot;. The Astronomical Journal 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782.&lt;/p&gt; &lt;p&gt;[2] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Dr&amp;#252;ckmuller, and Sebastian Deiries. 2019. &quot;Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006&amp;#160;P1 (Mcnaught) Through Temporal Mapping&quot;. Icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013.&lt;/p&gt;

The Thermal and Dynamical History of (3200) Phaethon and (155140) 2005 UD: Relationship to Geminid Meteors

&lt;p&gt;The near-Earth asteroids (NEAs) (3200) Phaethon and (155140) 2005 UD are thought to share a common origin, with the former exhibiting dust activity at perihelion that is thought to directly supply the Geminid meteor stream. Both of these objects currently have very small perihelion distances (0.140 and 0.163 au for Phaethon and 2005 UD, respectively), which results in them having perihelion temperatures of or exceeding 1000 K. NEA population models compared to observation suggest that low-perihelion objects are destroyed over time by a temperature-dependent mechanism that becomes relevant at heliocentric distances &lt; 0.3 au. Thus, the current activity from Phaethon is relevant to the destruction of NEAs close to the Sun, which most likely has produced meteor streams linked to asteroids in the past.&lt;/p&gt; &lt;p&gt;In this work, we model the past thermal characteristics of Phaethon and 2005 UD using a detailed thermophysical model (TPM) and orbital integrations of each object. Our aim is to investigate and inform a temperature-dependent mechanism responsible for Phaethon's dust activity and the destruction of NEAs at small heliocentric distances. We consider volatile sublimation and thermal fracturing as potential candidate processes. First, a TPM is used to calculate temperatures (surface and subsurface) along an entire orbit for a spherical object, given its semimajor axis and eccentricity (&lt;em&gt;a&lt;/em&gt; and &lt;em&gt;e&lt;/em&gt;). Temperature characteristics such as maximum daily temperature, maximum thermal gradient, and temperature at varying depths are extracted from the model, which is run for a predefined set of &lt;em&gt;a&lt;/em&gt; and &lt;em&gt;e&lt;/em&gt;. Next, dynamical integrations of orbital clones of Phaethon and 2005 UD are used to estimate the past orbital elements&amp;#160;of each object. These dynamical results are then combined with the temperature characteristics to model the past evolution of thermal characteristics.&lt;/p&gt; &lt;p&gt;We find that predictions of the orbital history for these objects is reasonably accurate up to ~100,000 yr in the past, and is characterized by cyclic changes in&amp;#160;&lt;em&gt;e&lt;/em&gt;&amp;#160;resulting in perihelia values periodically shifting between present-day values and 0.3 au. The thermal history of the maximum surface temperatures, for example, thus follows a pattern of extreme heating (up to 1000 K) every 20,000 yr. Currently, Phaethon is experiencing relatively large degrees of heating compared to the recent 20,000 yr. We find that even temperatures at-depth are too large over these timescales for water ice to be stable-unless actively supplied somehow and that thermal fracturing may be extremely effective at breaking down surface regolith. Observations of dust activity from the DESTINY+ flyby mission will provide important constraints on the mechanics of dust-loss.&lt;/p&gt; &lt;p&gt;Past estimates of Phaethon's dust tail and mass-loss rate assume particle size of &amp;#8776;1 micron and are insufficient to explain the entire mass of the Geminid stream of its ~1,000 year lifetime. However, observations of Geminid meteors show that it consists of a wide range of particle sizes (from micron-sized up to a few centimeters). Assuming a similar particle size distribution as the Geminids for Phaethon's dust tail we re-evaluate the mass-loss rate. We find that the annual dust activity from Phaethon may be sufficient to actively supply the Geminid stream in steady-state.&lt;/p&gt;

Dust tail observation and modeling of the interstellar comet 2I/Borisov

&lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;On 30 August 2019 the amateur Borisov discovered a new comet; after few days it was clear from the characteristics of its orbit (eccentricity &gt; 3 and high hyperbolic excess velocity) that the second interstellar object had been detected and the object received the name of 2I/Borisov. &lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;It appears to be very different from 1I/&amp;#8217;Oumuamua and can be considered as the first interstellar comet.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;According to the first observations the comet had a nucleus with a radius of few km and a dust coma and tail due to the activity started in June 2019 (Jewitt et al., 2019).&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;At the beginning of October we submitted the Discretionary Director Time (DDT) proposal to the TNG in order to monitor the comet. Some images have been acquired, in November and December 2019, with the DOLORES instrument in the R filter.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;We have applied the dust model described in Fulle et al. (2010), that has been tested on the comet 67P/Churyumov-Gerasimenko and validated with the Rosetta measurements.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;According to the results of our dust model and the activity model (Fulle et al., 2020) we derived a water flux from the nucleus of 8x10&lt;sup&gt;-6 &lt;/sup&gt;kg m&lt;sup&gt;-2 &lt;/sup&gt;s&lt;sup&gt;-1 &lt;/sup&gt;and a dust loss rate of 35 and 30 kg s&lt;sup&gt;-1 &lt;/sup&gt;in November and December 2019 respectively (Cremonese et al., 2020). This slight decrease has been observed around the perihelion on 8 December, few months later the comet fragmented.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;In this work we will describe the dust tail observations and the dust model results, even comparing them with the Jupiter family comet 67P.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Sectionheading&quot;&gt;&lt;span lang=&quot;EN-GB&quot;&gt;References&lt;/span&gt;&lt;span lang=&quot;EN-GB&quot;&gt;:&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Abstractsectionheading&quot;&gt;G.Cremonese, et al., 2020, ApJL, 893, L12&lt;/p&gt; &lt;p class=&quot;Abstractsectionheading&quot;&gt;M.Fulle et al., 2010, A&amp;A, 522, A63.&lt;/p&gt; &lt;p class=&quot;Abstractsectionheading&quot;&gt;M.Fulle et al., 2020, MNRAS, 493, 4039.&lt;/p&gt; &lt;p class=&quot;Abstractsectionheading&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;Jewitt et al., 2019, ApJ, 886, L29.&lt;/span&gt;&lt;/p&gt;

On the activity of comets: understanding the gas and dust emission from comet 67/Churyumov–Gerasimenko’s south-pole region during perihelion

ABSTRACT When comets approach the Sun, their surface is heated and the volatile species start to sublimate. Due to the increasing gas pressure, dust is ejected off the surface, which can be observed as cometary coma, dust tail, and trail. However, the underlying physical processes are not fully understood. Using state-of-the-art results for the transport of heat and gas as well as of the mechanical properties of cometary matter, we intend to describe the activity pattern of comets when they approach the Sun. We developed a novel thermophysical model to simulate the dust ejection from comet 67/Churyumov–Gerasimenko’s south-pole region at perihelion. Based on the input parameters, this model computes the sub-surface temperature profile, the pressure build-up, and the redistribution of volatiles inside the cometary sub-surface region and provides mass-loss rates of dust and gas as well as typical sizes and ice content of the ejected dust chunks. Our thermophysical model allows for continuous gas and dust ejection from the Southern hemisphere of comet 67/Churyumov–Gerasimenko at perihelion. We find that the model output is in general agreement with the observed Rosetta data. The sublimation of CO2 ice drives the ejection of very large ($\gtrsim 10\, \mathrm{cm}$) chunks, which contain $10\, {{\ \rm per\ cent}}$ to $90 \, {{\ \rm per\ cent}}$ of the initial water–ice content. In contrast, the outgassing of H2O ice causes the lift-off of small clusters of dust aggregates, which contain no ice.

Search for gas from the disintegrating rocky exoplanet K2-22b

Context. The red dwarf star K2-22 is transited every 9.14 h by an object which is best explained by being a disintegrating rocky exoplanet featuring a variable comet-like dust tail. While the dust is thought to dominate the transit light curve, gas is also expected to be present, either from being directly evaporated off the planet or by being produced by the sublimation of dust particles in the tail. Aims. Both ionized calcium and sodium have large cross-sections, and although present at low abundance, exhibit the strongest atomic absorption features in comets. We therefore also identify these species as the most promising tracers of circumplanetary gas in evaporating rocky exoplanets and search for them in the tail of K2-22 b to constrain the gas-loss and sublimation processes in this enigmatic object. Methods. We observed four transits of K2-22 b with X-shooter on the Very Large Telescope operated by ESO to obtain time series of intermediate-resolution (R ~ 11 400) spectra. Our analysis focussed on the two sodium D lines (588.995 and 589.592 nm) and the Ca+ triplet (849.802, 854.209, and 866.214 nm). The stellar calcium and sodium absorption was removed using the out-of-transit spectra. We searched for planet-related absorption in the velocity rest frame of the planet, which changes from approximately −66 to +66 km s−1 during the transit. Results. Since K2-22 b exhibits highly variable transit depths, we analysed the individual nights and their average. By injecting signals we reached 5σ upper limits on the individual nights that range from 11–13% and 1.7–2.0% for the sodium and ionized calcium absorption of the tail, respectively. Night 1 was contaminated by its companion star so we considered weighted averages with and without Night 1 and quote conservative 5σ limits without Night 1 of 9 and 1.4%, respectively. Assuming their mass fractions to be similar to those in the Earth’s crust, these limits correspond to scenarios in which 0.04 and 35% of the transiting dust is sublimated and observed as absorbing gas. However, this assumes the gas to be co-moving with the planet. We show that for the high irradiation environment of K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s of km s−1 owing to radiation pressure and entrainment by the stellar wind, making these species much more difficult to detect. No evidence for such possibly broad and blue-shifted signals are seen in our data. Conclusions. Future observations aimed at observing circumplanetary gas should take into account the possible broad and blue-shifted velocity field of atomic and ionized species.

Dust properties of double-tailed active asteroid (6478) Gault

Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt. Aims. We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s). Methods. We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid. Results. It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 × 107 kg and 1.6 × 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 μm–1 cm radius range, follows a broken power law with bending points near 15 μm and 870 μm. On the other hand, the photometric series indicate a nearly constant magnitude over several 5–7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust. Conclusions. The dust particles forming Gault’s tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.