Observations Of Comet Research Articles

Analytic and numerical methods for the Abel transform of exponential functions for planetary and cometary atmospheres

Line-of-sight integration of emissions from planetary and cometary atmospheres is the Abel transform of the emission rate, under the spherical symmetry assumption. Indefinite integrals constructed from the Abel transform integral are useful for implementing remote sensing data analysis methods, such as the numerical inverse Abel transform. We propose analytical expressions obtained by a suitable, non-alternating, series development to compute those indefinite integrals. We establish expressions allowing absolute accuracy control of the convergence of these series and illustrate how this accuracy depends on the number of terms involved in the series computation. We compare the analytical method with numerical computation techniques, which are found to be sufficiently accurate as well. Inverse Abel transform fitting is then tested in order to establish that the expected emission rate profiles can be retrieved from the observation of both planetary and cometary atmospheres. We show that the method is robust, i.e. that it can be applied even when the properties of the observed atmosphere depart from the assumed ones, especially when Tikhonov regularization is included. A first application is conducted over observation of comet 46P/Wirtanen, showing some variability, possibly attributable to an evolution of the contamination by dust and icy grains.

Dust Production of Interstellar Comet 2I/Borisov Throughout Perihelion

Abstract The recently discovered comet 2I/Borisov quickly became a prime target for comet observers during its perihelion approach in 2019 December, after it was discovered to be the first comet of interstellar origin. We present our observations and measurements of the dust production between 2019 October, when the interstellar comet became bright enough for small aperture telescopes, and 2020 January, when the comet entered the plane of the Milky Way. We observed the comet for 24 nights using three telescopes in the public iTelescope network. The telescopes spanned both the Northern and Southern hemispheres, were of similar aperture size (0.43–0.51 m), and employed a Johnson–Cousins R C filter. Using these data, we measure an A(0°)f ρ range of 94 ± 14 to 139 ± 34 cm, a dust production rate Q dust range of 11.2 ± 4.4 to 16.4 ± 7.3 kg s−1, and a dust-brightness profile-parameter range of −0.95 ± 0.11 to −1.81 ± 0.20 for the interstellar comet. This work revealed low dust production rates from the comet that remained consistent throughout its apparition, with no notable brightening or increase in dust production throughout the observing campaign.

Observations of distant comet C/2011 KP36 (Spacewatch): photometry, spectroscopy, and polarimetry

Aims. The main objective of our study is to obtain new observational results for the active long-period comet C/2011 KP36 (Spacewatch). This comet has unusual orbital properties and moves at distances larger than 5 au from the Sun. Methods. We carried out extensive observations of comet C/2011 KP36 (Spacewatch) at the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the focal reducer SCORPIO-2. We obtained quasi-simultaneous long-slit spectra in the visible, as well as photometric and linear polarimetric images with the g-sdss and r-sdss filters on November 25, 2016 when the heliocentric and geocentric distances of the comet were 5.06 au and 4.47 au, respectively. We modeled the behavior of the color and polarization in the coma, considering the dust as an ensemble of polydisperse nonspherical particles. Results. Two strong jet-like structures in solar and antisolar directions and two short and narrow jet features in the perpendicular direction were revealed in the coma. Our simulations showed that the latter two jets originated from the same active area. We determined the orientation of the rotation axis of the nucleus and the position of three active areas. High activity of the comet was characterized by Afρ values of 1065 ± 11 cm in the g-sdss filter and 1264 ± 17 cm in the r-sdss filter. The comet was found to be rich in CO+, while there was no clear detection of CN, C3, C2, and N2+. The dust color g–r varies over the coma from about 0.2m to 0.7m, and the linear polarization degree from about −1% to −6% at the phase angle 9.6°. The color of the nucleus of comet C/2011 KP36 (Spacewatch) is ultrared, B – R = 1.9m ± 0.3m. Conclusions. The high variability of the observed characteristics over the coma of comet C/2011 KP36 (Spacewatch) indicates significant and variable activity of the nucleus with, probably, numerous small active areas. Together with the three identified large active areas, they are characterized by different combinations of water ice, CO2 ice, and refractory dust and sizes of their particles, which are in the micron-size range.

Spatial Distribution of Ultraviolet Emission from Cometary Activity at 67P/Churyumov-Gerasimenko

Abstract The Alice ultraviolet spectrograph on board the Rosetta orbiter provided the first near-nucleus ultraviolet observations of a cometary coma from arrival at comet 67P/Churyumov-Gerasimenko in 2014 August through 2016 September. The characterization of atomic and molecular emissions in the coma revealed the unexpected contribution of dissociative electron impact emission at large heliocentric distances and during some outbursts. This mechanism also proved useful for compositional analysis, and Alice observed many cases that suggested elevated levels of the supervolatile O2, identifiable in part to their emissions resulting from dissociative electron impact. In this paper, we present the first two-dimensional UV maps constructed from Alice observations of atomic emission from 67P during an increase in cometary activity on 2015 November 7–8. Comparisons to observations of the background coma and an earlier collimated jet are used to describe possible changes to the near-nucleus coma and plasma. To verify the mapping method and place the Alice observations in context, comparisons to images derived from the MIRO and VIRTIS-H instruments are made. The spectra and maps we present show an increase in dissociative electron impact emission and an O2/H2O ratio of ∼0.3 for the activity; these characteristics have been previously identified with cometary outbursts seen in Alice data. Further, UV maps following the increases in activity show the spatial extent and emission variation experienced by the near-nucleus coma, informing future UV observations of comets that lack the same spatial resolution.

Discovery of Carbon Monoxide in Distant Comet C/2017 K2 (PANSTARRS)

Abstract Optical observations of the Oort cloud comet C/2017 K2 (PANSTARRS) show that its activity began at large heliocentric distances (up to 35 au), which cannot be explained by either the sublimation or the crystallization of water ice. Supervolatile sublimation, most likely of carbon monoxide (CO), has been proposed as a plausible driver of the observed mass loss. Here, we present the detection of the J = 2−1 rotational transition in outgassed CO from C/2017 K2 when at heliocentric distance r H = 6.72 au, using the James Clerk Maxwell Telescope. The CO line is blueshifted by 0.20 ± 0.03 km s−1 with an area and width of 8.3 ± 2.3 mK km s−1 and 0.28 ± 0.08 km s−1, respectively. The CO production rate is Q CO = (1.6 ± 0.5) × 1027 s−1. These are the first observations of a gaseous species in C/2017 K2 and provide observational confirmation of the role of supervolatile sublimation in this comet.

Narrowband Observations of Comet 46P/Wirtanen during Its Exceptional Apparition of 2018/19. II. Photometry, Jet Morphology, and Modeling Results

Abstract We report on our extensive photometry and imaging of comet 46P/Wirtanen during its 2018/19 apparition and use these data to constrain the modeling of Wirtanen’s activity. Narrowband photometry was obtained in 9 epochs from 2018 October through 2019 March as well as 10 epochs during the 1991, 1997, and 2008 apparitions. The ensemble photometry reveals a typical composition and a secular decrease in activity since 1991. Production rates were roughly symmetric around perihelion for the carbon-bearing species (CN, C3, and C2), but steeper for OH and NH outbound. Our imaging program emphasized CN, whose coma morphology and lightcurve yielded rotation periods reported in a companion paper (Farnham et al. 2021). Here, we compare the gas and dust morphology on the 18 nights for which observations of additional species were obtained. The carbon-bearing species exhibited similar morphology that varied with rotation. OH and NH had broad, hemispheric brightness enhancements in the tailward direction that did not change significantly with rotation, which we attribute to their originating from a substantial icy grain component. We constructed a Monte Carlo model that replicates the shape, motion, and brightness distribution of the CN coma throughout the apparition with a single, self-consistent solution in principal axis rotation. Our model yields a pole having (R.A., decl.) = 319°, −5° (pole obliquity of 70°) and two large sources (radii of 50° and 40°) centered at near-equatorial latitudes and separated in longitude by ∼160°. Applications of the model to explain observed behaviors are discussed.

Jan Walery Jędrzejewicz (1835–1887) and his Observations of Comets

Jan Walery Jędrzejewicz was a medical doctor with active practice in Płońsk and an astronomer by passion. In fact, astronomy was a second profession for ‘Dr. Jedrzejewicz’, as he signed his astronomical publications. He built his own observatory in Płońsk, small village situated about 70 km from Warsaw, which he equipped with professional instruments. Thanks to that, he could perform precise astronomical observations. In the astronomical community, he was known and esteemed for his precise measurements of double stars. He also measured the position of many comets discovered at that times, including long-period ones. This study is devoted to the analysis of precision of Jędrzejewicz measurements on the examples of three long-period comets, today known as C/1885 X1 Fabry, C/1885 X2 Barnard and C/1886 T1 Barnard-Hartwig.

Cold Traps of Hypervolatiles in the Protosolar Nebula at the Origin of the Peculiar Composition of Comet C/2016 R2 (PanSTARRS)

Abstract Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N2/CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N2 ice lines. Moreover, high CO/H2O ratios (>100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N2/CO and CO/H2O ratios consistent with the measurements made in R2’s coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.

Unusual polarimetric properties for interstellar comet 2I/Borisov

So far, only two interstellar objects have been observed within our Solar System. While the first one, 1I/‘Oumuamua, had asteroidal characteristics, the second one, 2I/Borisov, showed clear evidence of cometary activity. We performed polarimetric observations of comet 2I/Borisov using the European Southern Observatory Very Large Telescope to derive the physical characteristics of its coma dust particles. Here we show that the polarization of 2I/Borisov is higher than what is typically measured for Solar System comets. This feature distinguishes 2I/Borisov from dynamically evolved objects such as Jupiter-family and all short- and long-period comets in our Solar System. The only object with similar polarimetric properties as 2I/Borisov is comet C/1995 O1 (Hale-Bopp), an object that is believed to have approached the Sun only once before its apparition in 1997. Unlike Hale-Bopp and many other comets, though, comet 2I/Borisov shows a polarimetrically homogeneous coma, suggesting that it is an even more pristine object.

The Reactivation of Main-belt Comet 259P/Garradd (P/2008 R1)

Abstract We present observations of main-belt comet (MBC) 259P/Garradd from 4 months prior to its 2017 perihelion passage to 5 months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of M ̇ d = ( 4.6 ± 0.2 ) kg s−1 (assuming grain densities of ρ = 2500 kg m−3 and a mean effective particle size of a ¯ d = 2 mm) and a best-fit start date of detectable activity of 2017 April 22 ± 1, when the object was at a heliocentric distance of r h = 1.96 ∓ 0.03 au and a true anomaly of ν = 313.°9 ± 0.°4. We estimate the effective active fraction of 259P’s surface area to be from f act ∼ 7 × 10−3 to f act ∼ 6 × 10−2 (corresponding to effective active areas of A act ∼ 8 × 103 m2 to A act ∼ 7 × 104 m2) at the start of its 2017 active period. A comparison of estimated total dust masses measured for 259P in 2008 and 2017 shows no evidence of changes in activity strength between the two active apparitions. The heliocentric distance of 259P’s activity onset point is much smaller than those of other MBCs, suggesting that its ice reservoirs may be located at greater depths than on MBCs farther from the Sun, increasing the time needed for a solar-irradiation-driven thermal wave to reach subsurface ice. We suggest that deeper ice on 259P could be a result of more rapid ice depletion caused by the object’s closer proximity to the Sun compared to other MBCs.

Mid-infrared observations of the nucleus of Comet P/2016 BA14 (PANSTARRS)

We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of 1.012 au and 0.026 au, respectively, approximately 30 h before its closest approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution (λ/Δλ ~ 250) spectroscopic observations in the N-band and imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 μm) in the N- and Q-bands were obtained using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14 at different wavelengths are consistent with a point-spread function. Owing to the close approach of the comet to the Earth, the observed thermal emission from the comet is dominated by the thermal emission from its nucleus rather than its dust coma. The observed spectral energy distribution of the nucleus at mid-infrared wavelengths is consistent with a Planck function at temperature T ~ 350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by assuming an emissivity of 0.97). The normalized emissivity spectrum of the comet exhibits absorption-like features that are not reproduced by the anhydrous minerals typically found in cometary dust coma, such as olivine and pyroxene. Instead, the spectral features suggest the presence of large grains of phyllosilicate minerals and organic materials. Thus, our observations indicate that an inactive small body covered with these processed materials is a possible end state of comets.

First Comet Observations with NIRSPEC-2 at Keck: Outgassing Sources of Parent Volatiles and Abundances Based on Alternative Taxonomic Compositional Baselines in 46P/Wirtanen

Abstract A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H2O and CH3OH. Abundances of volatiles are reported relative to H2O, as traditionally done, as well as C2H6. While not unique, the choice of C2H6 demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional “baselines” and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target.

Photometry and polarimetry of comet 46P/Wirtanen in the 2018 apparition

Abstract Extensive photometric and polarimetric observations of comet 46P/Wirtanen within the framework of the international 4*P Coma Morphology Campaign were conducted from August 16, 2018 to February 13, 2019 using five telescopes. Digital processing applied to the direct images of the comet revealed the coma and tail, which varied in shape and size. The jet at the position angle 133.5° was found in the images obtained on December 7 and 9, 2018 in the V and R filters. From modelling the formation of the jet, we calculated the coordinates of the north pole of the nucleus rotation axis, α = 220° ± 10°, δ = –20° ± 8°, and the cometocentric latitude of the active area on the nucleus L = 20° ± 6°. The velocity of matter outflow from this active area was estimated to be 0.5 ± 0.05km/ s. The dust production Afρ changed from 12 to 88cm. During our observation period, the coma colour varied from 0.76m to 0.87m and from 0.38m to 0.50m and the reflectivity gradient from 11 to 16.2 per cent per 1000Å and 5.8 to 15.4 per cent per 1000Å for the B–V and V–R spectral bands, respectively. The comparison of the dust production rate of comet 46P/Wirtanen until 2018 and our data for 2018 apparition confirmed its great decrease. The degree of polarization of comet 46P was measured at the phase angles from 27° to 37°. In order to reliably retrieve the polarimetric class of comet 46P, observations at large phase angles are required.

Transport Characteristics of the Near-Surface Layer of the Nucleus of Comet 67P/Churyumov–Gerasimenko

The paper considers the free molecular flow of gas through the dusty porous surface layer of a comet nucleus. The study is based on computer models of generation of a porous medium and Knudsen gas diffusion. We consider various types of homogeneous and heterogeneous layers constructed from nonintersecting spheres, including layers that contain microcracks or inner cavities. Using the test-particle method, we quantitatively estimate the free path distribution function, layer permeability, and effective kinetic characteristics of sublimation products passing through a nonisothermal porous layer. In addition, in this approach, we consider the volumetric absorption of visible solar radiation in the near-surface absorbing layer. Simple approximation expressions are obtained for all the transport characteristics under study, which makes it possible to estimate the characteristics with sufficient accuracy for practical applications in the physics of comets. The results will be used to construct new consistent models of energy transfer in the near-surface layer of a comet nucleus and, first of all, to analyze the results of the observations of comet 67P/Churyumov‒Gerasimenko.

Narrowband Observations of Comet 46P/Wirtanen during Its Exceptional Apparition of 2018/19. I. Apparent Rotation Period and Outbursts

Abstract We obtained broad- and narrowband images of the hyperactive comet 46P/Wirtanen on 33 nights during its 2018/2019 apparition, when the comet made a historic close approach to the Earth. With our extensive coverage, we investigated the temporal behavior of the comet on both seasonal and rotational timescales. We used CN observations to explore the coma morphology, revealing that there are two primary active areas that produce spiral structures. The direction of rotation of these structures changes from pre- to postperihelion, indicating that the Earth crossed the comet’s equatorial plane sometime around perihelion. We also used the CN images to create photometric light curves that consistently show two peaks in the activity, confirming the two source regions. We measured the nucleus’s apparent rotation period at a number of epochs using both the morphology and the light curves. These results all show that the rotation period is continuously changing throughout our observation window, increasing from 8.98 hr in early November to 9.14 hr around perihelion and then decreasing again to 8.94 hr in February. Although the geometry changes rapidly around perihelion, the period changes cannot be primarily due to synodic effects. The repetition of structures in the coma, both within a night and from night to night, strongly suggests that the nucleus is in a near-simple rotation state. We also detected two outbursts, one on December 12 and the other on January 28. Using the apparent velocities of the ejecta in these events, 68 ± 5 and 162 ± 15 m s−1, respectively, we derived start times of 2018 December 12 at 00:13 UT ± 7 minutes and 2019 January 27 at 20:01 UT ± 30 minutes.

FUV Observations of the Inner Coma of 46P/Wirtanen

Abstract Far-ultraviolet observations of comets yield information about the energetic processes that dissociate the sublimated gases from their primitive surfaces. Understanding which emission processes are dominant, their effects on the observed cometary spectrum, and how to properly invert the spectrum back to the composition of the presumably pristine surface ices of a comet nuclei are all critical components for proper interpretation and analysis of comets. The close approach of comet 46P/Wirtanen in 2018–2019 provided a unique opportunity to study the innermost parts of a cometary coma with the Hubble Space Telescope Cosmic Origins Spectrograph, rarely accessible with remote observations, at length scales (hundreds of kilometers) and wavelengths (900–1430 Å) previously probed only by the European Space Agency’s Rosetta spacecraft. Our observations show a complex picture for the inner coma; atomic production rates for H and O that show water is the dominant source of both, an abundance of atomic sulfur that is difficult to explain with the lifetimes of common sulfur parent molecules, and a density distribution that is poorly fit with both Haser and vectorial models.

Dust Production from Mini Outbursts of Comet 29P/Schwassmann-Wachmann 1

Abstract Here we report on the results of observations of comet 29P/Schwassmann-Wachmann 1 obtained using four telescopes, in three different countries, from 2019 September 25 to 2020 January 19. During the last four months of 2019, comet 29P/Schwassmann-Wachmann 1 exhibited new outburst behavior indicative of small or mini outbursts in which the brightening of the comet lasted from only a few days to more than a week. We used Johnson-Cousins R C-band multi-aperture photometry measurements to calculate the dust production, via Afρ, the dust production rate, and the dust brightness profile of the comet for each night of observations. During these observations, the brightness of the comet fluctuated significantly multiple times, with notable changes in brightness ranging from 0.41 to 0.71 mag over time periods of only a couple of days to nearly two weeks.

MUSE observations of comet 67P/Churyumov-Gerasimenko

Aims. Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion between 3 and 7 March 2016. These observations are part of a simultaneous ground-based campaign aimed at providing broad-scale information about comet 67P to complement the ESA/Rosetta mission. Methods. We obtained a total of 38 datacubes over five nights. We took advantage of the integral field unit nature of the instrument to carry out a simultaneous study of the spectrum of 67P’s dust and its spatial distribution in the coma. We also looked for evidence of gas emission in the coma. Results. We produced a high-quality spectrum of the dust coma over the optical range that could be used as a reference for future comet observations with this instrument. The slope of the dust reflectivity is of 10%∕100 nm over the 480–900 nm interval, with a shallower slope towards redder wavelengths. We used the Afρ to quantify the dust production and measure values of 65 ± 4 cm, 75 ± 4 cm, and 82 ± 4 cm in the V, R, and I bands, respectively. We detected several jets in the coma as well as the dust trail. Finally, using a novel method combining spectral and spatial information, we detected the forbidden oxygen emission line at 630 nm. Using this line, we derived a water production rate of 1.5 ± 0.6 × 1026 molec. s−1, assuming all oxygen atoms come from the photo-dissociation of water.

What Does It Mean to be a “Depleted” Comet? High Spectral Resolution Observations of the Prototypical Depleted Comet 21P/Giacobini–Zinner from the McDonald Observatory

Abstract We present high spectral resolution optical observations of comet 21P/Giacobini–Zinner from six nights in 2018. The observations were obtained with the Tull Coudé Spectrograph on the 2.7 m Harlan J. Smith Telescope of the McDonald Observatory. This comet’s spectrum shows strong depletions in C2, C3, CH, and NH2 relative to CN. We explore what it means for a comet to be depleted and show that all of the species are present in the spectrum at similar relative line intensities within a a molecular band compared with a typical comet. The depletions represent a much lower abundance of the species studied.

Optical observations of near isotropic comet C/2006 OF2 (Broughton) at two different heliocentric distances

Spectra and images of comet C/2006 OF2 (Broughton) were obtained with the 4.2-m William Herschel Telescope (La Palma, Spain) and with the 6-m Big Telescope Alt-azimuth (SAO RAN, Russia) at two observing epochs on October 15, 2007 and December 05, 2008.The comet was at heliocentric distances of 4.24 au and 2.59 au before and after the perihelion, respectively. The emissions CN 0–0, 0–1 (B2Σ+ − X2Σ+), C3 (A1Πu − X1Σg+) bands and C2 0–0 (A3Πg – X3Πu) of the Swan band system were identified in the post-perihelion cometary spectrum. Using the simple Haser model, the gas production rates of CN, C2 and C3 molecules were estimated at level of 1.35 × 1024 mol/s, 0.45 × 1024 mol/s, and 0.12 × 1024 mol/s, respectively. The gas production rate ratios, log(C2/CN) = −0.48 and log(C3/CN) = −1.05, point out that comet C/2006 OF2 probably belongs to the group of “carbon-chain depleted” comets. The ratios between C2, C3 and CN abundances of comet C/2006 OF2 are similar to those recently measured for interstellar comet 2I/Borisov at comparable heliocentric distances. The normalized reflectivity gradients of 12.7 ± 0.2%/1000 Å and − 2.3 ± 0.2%/1000 Å were calculated from the post perihelion spectrum in the intervals 4450 Å – 5500 Å and 5500–6935 Å, respectively, using the spectral regions free from comet emissions. The continuum slope, measured in the interval 4200 Å – 4800 Å, is even steeper, reaching 32.7 ± 0.2%/1000 Å. The normalized reflectivity gradient measured from a pair of the pre-perihelion V and R-images varies between 8%/1000 Å and 11%/1000 Å in the inner part of the coma, which exceeds the value obtained from the similar spectral interval of the post-perihelion spectrum, indicating that the coma became bluer after the perihelion passage. The morphology of the pre-perihelion images of the comet is governed by faint morphological features hidden in the bright coma. The color of the jets isolated from the pre-perihelion images is redder than the color of the ambient coma. The pre- and post-perihelion V-band Afρ parameters were found to be 1990 ± 90 cm and 2500 ± 100 cm for heliocentric distances of 4.24 au and 2.59 au, respectively.