Dust Tails Of Comets Research Articles

Observations of a dust tail gap in comet C/2014 Q1 (PanSTARRS)

Cometary dust tails display a wide array of structures, most believed to be caused by a variable dust production, size distributions, fragmentation processes, and interactions with the solar wind, e.g. Price et al. (2019). However, not all these structures are fully understood. Here we report the discovery of a curious new dust tail feature, first noted in long period comet C/2014 Q1 (PanSTARRS) (Bolin et al., 2014), where a section of the dust tail was clearly missing. This implies that the comet underwent a dramatic temporary decrease in dust production near perihelion. The gap appeared on 2015 July 14, 8 days after perihelion at 0.318 au, and progressed along the tail, following the expected motion of the dust that should have been present. The gap corresponds to dust ejected between July 5 and July 12, and of β>0.01. Possible explanations for this gap are proposed.

Fine-scale structure in cometary dust tails II: Further evidence for a solar wind influence on cometary dust dynamics from the analysis of striae in comet C/2011 L4 Pan-STARRS

Striated features, or striae, form in cometary dust tails due to an as-yet not fully constrained process or processes. Using STEREO-B SECCHI HI-1 instrument data, we display the evolution of striae in the tail of C/2011 L4 Pan-STARRS over a period of 8 days. This includes a period of morphological changes on 2013 March 14–15, similar to the reorganisation of striae previously observed in the tail of C/2006 P1 McNaught. This reorganisation is again attributed to Lorentz forces caused by the comet’s dust tail crossing the heliospheric current sheet. We further analyse the alignments of reorganised striae at both C/2006 P1 and C/2011 L4 and show these alignments have mixed compatibility with an additional solar wind influence. We also report the discovery of a bright neutral sodium tail at C/2011 L4.

Finite Lifetime Fragment Model 3 for striae formation in the dust tails of comets (FLM 3)

The striations in the Type II tail of the comets are called striae. The origin of the striae has been poorly understood. We present a new dynamical model to explain the structure of the striae observed at comets Hale-Bopp (C/1995O1), West (C/1975V1), and Seki-Lines (C/1962C1). Complex particles of absorbent and refractory particles with a radius of less than 1 μm are ejected from the nucleus of the comet and repeatedly decay to form striae with a lifetime of less than about 100 days at 1 AU. They continue to decay further and eventually disappear from sight. The above material science processes are explained by the following dynamical model. The particles ejected from the nucleus of a comet are assumed to be subjected to three forces: solar gravity, solar radiation pressure, and electromagnetic force. As the particle ejected from the nucleus of a comet decreases in size, the radiation pressure increases, decreases, increases and decreases or increases and decreases, forming a stria. The electromagnetic force is treated as an approximate theory and considered as a perturbation. This model is less of a dynamical approximation than previous theories, explains the structure of the striae, and also allows us to predict their luminosity and elucidate the origin of the striae.

Three case reports on the cometary plasma tail in the historical documents

Cometary tails visually manifest the solar wind and became an initial hint for its discovery. While the solar wind is being directly monitored with satellites, its time series before the space age has been controversially reconstructed with multiple proxies. Recently, archival reports of cometary plasma tails have been subjected to consideration to indirectly measure the solar wind but brought conclusion that no plasma tails had been reported prior to 1769 probably due to their brightness. However, historical records have occasionally reported comets with two tails even before 1769. These cases have been tentatively associated with visual reports of cometary plasma and dust tails. Therefore, we examined three such cases (C/1577 V1, 1P/837, and 1P/760), and compared the descriptions in historical records with calculated direction of their plasma tails. Our comparisons show that the records and calculations agree in these cases and plasma tails were visually recorded corresponding to these three great comets. These cases certify the capability of plasma tail observations with the unaided eye even before 1769, qualitatively imply their extreme brightness, proximities with the Sun and the Earth, relative enhancements of UV radiations, and interaction of cometary neutral atmosphere with solar wind plasma and magnetic field, while the lack of their detailed length or kink hinders us from their quantitative measuring. Further investigations will likely lead to the re-discovery of even more visual evidence of cometary plasma tails and, hence, improve our understanding on past space climate.

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.

Energetic Particle Showers Over Mars from Comet C/2013 A1 Siding Spring

AbstractThis paper is a phenomenological description of multispacecraft observations of energetic particles caused by the close flyby of comet C/2013 A1 Siding Spring with Mars on 19 October 2014. This is the first time that cometary energetic particles have been observed at Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN)‐solar energetic particle (SEP) and the Mars Odyssey‐High Energy Neutron Detector (HEND) instruments recorded evidence of precipitating particles, which are likely O+ pickup ions, during the ~10 hr that Mars was within the region of the comet's coma. O+ pickup ions were also detected several hours after, although whether their origin is the comet or space weather is not conclusive. We discuss the possible origin of those particles and also the cause of an additional shower of energetic particles that HEND observed between 22 and 35 hr after the comet's closest approach, which may be related to dust impacts from the comet's dust tail. An O+ pickup ion energy flux simulation is performed with representative solar wind and cometary conditions, together with a simulation of their energy deposition profile in the atmosphere of Mars. Results indicate that the O+ pickup ion fluxes observed by SEP were deposited in the ionosphere around 105 to 120 km altitude, and they are compared with precomet flyby estimations of cometary pickup ions. The comet's flyby deposited a significant fluence of energetic particles into Mars' upper atmosphere, at a similar level to a large space weather event.

Fine-scale structure in cometary dust tails I: Analysis of striae in Comet C/2006 P1 (McNaught) through temporal mapping

Striated features, or striae, form in cometary dust tails due to an as-yet unconstrained process or processes. For the first time we directly display the formation of striae, at C/2006 P1 McNaught, using data from the SOHO LASCO C3 coronagraph. The nature of this formation suggests both fragmentation and shadowing effects are important in the formation process. Using the SOHO data with STEREO-A and B data from the HI-1 and HI-2 instruments, we display the evolution of these striae for two weeks, with a temporal resolution of two hours or better. This includes a period of morphological change on 2007 January 13–14 that we attribute to Lorentz forces caused by the comet’s dust tail crossing the heliospheric current sheet. The nature of this interaction also implies a mixing of different sized dust along the striae, implying that fragmentation must be continuous or cascading. To enable this analysis, we have developed a new technique – temporal mapping – that displays cometary dust tails directly in the radiation beta (ratio of radiation pressure to gravity) and dust ejection time phase space. This allows for the combination of various data sets and the removal of transient motion and scaling effects.

Mt. Wendelstein imaging of the post-perihelion dust coma of 67P/Churyumov–Gerasimenko in 2015/2016

Comet 67P/Churyumov-Gerasimenko (67P) was imaged with the 2m telescope at Mt. Wendelstein Observatory in the Alps. Coma and tail monitoring was performed during 51 nights between 22 August 2015 and 9 May 2016. The images through r and i Sloan Digital Sky Survey (SDSS) filters show the dust distribution around the comet, while images in the SDSS g filter indicate also the presence of coma gas in early September 2015. The dust color of 67P implies intrinsic reddening of 9 %/100nm. After maximum shortly after perihelion passage the dust activity decreased with a heliocentric exponent of 4.1 to 4.2 from late September 2015 until May 2016. The opposition surge during early 2016 can be explained by a linear light scattering phase function (beta ~ 0.04) or an asteroid-like HG-type phase function (G ~ 0.15). The radial brightness profile indicates a 'quasi-steady-state' dust coma from late September to the end of 2015. Dust fragmentation during about a month after perihelion may be responsible for radial coma profiles with slopes below unity, while dust accumulation due to very slow dust expansion velocity may result in steeper than unity profiles during 2016. Three fan-shape dust structures are characterized in the coma of 67P. A short dust ejection event on 22 -23 August 2015 has produced a dust arc-let and jet feature in the coma. In September 2015 the appearance of cometary dust tail is dominated by young dust produced around perihelion. The older dust dominates the tail appearance as of mid November 2015.

The reactivation of main-belt Comet 324P/La Sagra (P/2010 R2)

Abstract We present observations using the Baade Magellan and Canada–France–Hawaii telescopes showing that main-belt comet 324P/La Sagra, formerly known as P/2010 R2, has become active again for the first time since originally observed to be active in 2010–2011. The object appears point-source-like in 2015 March and April as it approached perihelion (true anomaly of ν ∼ 300°), but was ∼1 mag brighter than expected if inactive, suggesting the presence of unresolved dust emission. Activity was confirmed by observations of a cometary dust tail in 2015 May and June. We find an apparent net dust production rate of ${\dot{M}_{\rm d}}\lesssim 0.1$ kg s−1 during these observations. 324P is now the fourth main-belt comet confirmed to be recurrently active, a strong indication that its activity is driven by sublimation. It now has the largest confirmed active range of all likely main-belt comets, and also the most distant confirmed inbound activation point at R ∼ 2.8 au. Further observations during the current active period will allow direct comparisons of activity strength with 324P's 2010 activity.

The formation of striae within cometary dust tails by a sublimation-driven YORP-like effect

Sublimating gas molecules scatter off of the surface of an icy body in the same manner as photons (Lambertian Scattering). This means that for every photon-driven body force, there should be a sublimation-driven analog that affects icy bodies. Thermal photons emitted from the surfaces of asymmetrically shaped bodies in the Solar System generate net torques that change the spin rates of these bodies over time. The long-term averaging of this torque is called the YORP effect. Here we propose a sublimation-driven analog to the YORP effect (Sublimation-YORP or SYORP), in which sublimating gas molecules emitted from the surfaces of icy bodies in the Solar System also generate net torques on the bodies. However, sublimating gas molecules carry ∼104–105 times more momentum away from the body than thermal photons, resulting in much greater body torques. Previous studies of sublimative torques focused on emissions from highly localized sources on the surfaces of Jupiter Family Comet nuclei, and have therefore required extensive empirical observations to predict the resulting behavior of the body. By contrast, SYORP applies to non-localized emissions across the entire body, which likely dominates sublimation-drive torques on small icy chunks and dynamically young comets outside the Jupiter Family, and can therefore be applied without high-resolution spacecraft observations of their surfaces. Instead, we repurpose the well-tested mathematical machinery of the YORP effect to account for sublimation-driven torques. We show how an SYORP-driven mechanism best matches observations of the rarely observed, Sun-oriented linear features (striae) in the tails of comets, whose formation mechanism has remained enigmatic for decades. The SYORP effect naturally explains why striae tend to be observed between near-perihelion and ∼1AU from the Sun for comets with perihelia less than 0.6AU, and solves longstanding problems with moving enough material into the cometary tail to form visible striae. We show that the SYORP mechanism can form striae that match the striae of Comet West, estimate the sizes of the stria-forming chunks, and produce a power-law fit to these parent chunks with a power law index of -1.4-0.6+0.3. Lastly, we predict potential observables of this SYORP mechanism, which may appear as clouds or material that appear immediately prior to stria formation, or as a faint, wispy dust feature within the dust tail, between the nucleus and the striae.

Modeling of the dust tail of comet C/2012 S1 (ISON) from the results of observations

The results of the dynamic modeling of the process, that formed the dust tail of comet C/2012 S1 (ISON), are presented. The images of the comet were acquired with the 1-meter Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). To construct the model of the dust tail, the trajectories of 50 million dust particles were traced. The distribution of brightness in the dust tail of the comet was reproduced in the model. According to our model investigations, the observed tail could be formed by dust particles with the sizes ranging from 0.5 to 16.6 µm and the escape velocities from 17 to 130 m/s; the power exponent of the distribution by radius is–2.5, and the maximum age of the dust particles having formed the cometary tail is 25 days. In the paper, the brightness of the comet at the moment of observations is also estimated, and the morphology of the cometary coma is analyzed with the use of digital filters.

Model analysis of the dust tail of comet C/2012 K5 (LINEAR)

From the dynamic modeling of the process forming the dust tail of comet C/2012 K5 (LINEAR), the brightness distribution in this dust tail has been retrieved. The model developed by Korsun on the basis of the statistical Monte-Carlo approach was used. The adequacy of the model was determined by fitting the observed and modeled isophots. The following parameters of dust particles composing the dust component of the cometary atmosphere have been estimated: the range of radii (0.7–100 μm), the power index of the size distribution law (–2.4), the range of velocities (6–135 m/s), and the maximum age of dust particles (88 days).

CONSTRAINING THE DUST COMA PROPERTIES OF COMET C/SIDING SPRING (2013 A1) AT LARGE HELIOCENTRIC DISTANCES

The close encounter of Comet C/2013 A1 (Siding Spring) with Mars on October 19, 2014 presented an extremely rare opportunity to obtain the first flyby quality data of the nucleus and inner coma of a dynamically new comet. However, the comet's dust tail potentially posed an impact hazard to those spacecraft. To characterize the comet at large heliocentric distances, study its long-term evolution, and provide critical inputs to hazard modeling, we imaged C/Siding Spring with the Hubble Space Telescope when the comet was at 4.58, 3.77, and 3.28 AU from the Sun. The dust production rate, parameterized by the quantity Af$\rho$, was 2500, 2100, and 1700 cm (5000-km radius aperture) for the three epochs, respectively. The color of the dust coma is 5.0$\pm$0.3$\%$/100 nm for the first two epochs, and 9.0$\pm$0.3$\%$/100 nm for the last epoch, and reddens with increasing cometocentric distance out to ~3000 km from the nucleus. The spatial distribution and the temporal evolution of the dust color are most consistent with the existence of icy grains in the coma. Two jet-like dust features appear in the north-northwest and southeast directions projected in the sky plane. Within each epoch of 1-2 hour duration, no temporal variations were observed for either feature, but the PA of the southeastern feature varied between the three epochs by ~30$^\circ$. The dust feature morphology suggests two possible orientations for the rotational pole of the nucleus, (RA, Dec) = (295$^\circ\pm$5$^\circ$, +43$^\circ\pm$2$^\circ$) and (190$^\circ\pm$10$^\circ$, 50$^\circ\pm$5$^\circ$), or their diametrically opposite orientations.

A dynamical analysis of the dust tail of Comet C/1995 O1 (Hale–Bopp) at high heliocentric distances

Comet C/1995 O1 (Hale–Bopp) has provided an unprecedented opportunity to observe a bright comet over a wide range of heliocentric distances. We present here Spitzer Space Telescope observations of Hale–Bopp from 2005 to 2008 that show a distinct coma and tail, the presence of which is uncommon given its large heliocentric distance (21.6AU and 27.2AU, respectively). The morphology of the dust is compared to dynamical models to understand the activity of the comet. Our analysis shows that the shape of Hale–Bopp’s dust tail in these images cannot be explained using the usual Finson–Probstein (solar gravity+solar radiation pressure) dynamical model. Several alternative explanations are explored. The analysis suggests that the most likely cause of the discrepancy is that the dust is being charged by the solar wind, then being affected by the interplanetary magnetic field via the Lorentz force. Though this effect has been explored previously, if correct, this seems to be the first time that the Lorentz force has been required to model a cometary dust tail. The analysis also suggests that Hale–Bopp was actively emitting particles when these images were taken, and the tail characteristics changed between observations.

The formation of striated structures in dust tails of comets

The formation of striated structures in dust tails of comets

Magnetopause displacements: the possible role of dust

Abstract. Large compressions of the magnetopause are proposed to occasionally result from temporary encounters of the magnetosphere with dust streams in interplanetary space. Such streams may have their origin in cometary dust tails or asteroids which cross the inner heliosphere or in meteoroids in Earth's vicinity. Dust ejected from such objects when embedding the magnetosphere for their limited transition time should cause substantial global deformations of the magnetopause/magnetosphere due to the very large dust grain mass and momentum which compensates for the low dust density when contributing to the upstream pressure variation.

Physical properties of cometary dust from Monte Carlo analysis of tail and coma images

Forward and inverse Monte Carlo modeling of cometary dust tail and coma images has provided one of the best approaches to infer the basic physical dust parameters and their time dependence: mass loss rates, ejection velocities, and size distribution functions. These methods attempt to fit the brightness distribution found in cometary astronomical images at a variety of wavelengths. The trajectories and the light scattered by the dust particles are functions of the size parameter, shape, and refractive index. In this paper we describe briefly the Monte Carlo technique, and present some applications.

Properties of the dust cloud caused by the Deep Impact experiment

We present an analysis of the observations of the Deep Impact event performed by the OSIRIS narrow angle camera aboard the Rosetta spacecraft over two weeks, in an effort to characterize the cometary dust grains ejected from the nucleus of Comet 9P/Tempel 1. We adopt a Monte Carlo approach to generate calibrated synthetic images, and a linear combination of them is fitted to the calibrated images so as to determine the physical parameters of the dust cloud. Our model considers spherical olivine particles with a density of 3780 kg m −3. It incorporates constraints on the direction of the cone of emission coming from additional images obtained at Pic du Midi observatory, and constraints on the dust terminal velocities coming from the physics of the impact. We find that the slope of the differential dust size distribution of grains with radii <20 μm ( β > 0.008 ) is 3.1 ± 0.3 , a value typical of cometary dust tails. This shows that there is no evidence in our data for an enhancement in sub-micron particles in the ejecta compared to the typical dust distribution of active comets. We estimate the mass of particles with radii <1.4 μm ( β > 0.14 ) to be 1.5 ± 0.2 × 10 5 kg . These particles represent more than 80% of the cross-section of the observed dust cloud. The mass carried by larger particles depends whether the gas significantly increases the kinetic energy of the grains in the inner coma; it lies in the range 1 – 14 × 10 6 kg for particles with radii <100 μm ( β > 0.002 ). We obtain the distribution of terminal velocities reached by the dust after the dust–gas interaction which is very well constrained between 10 and 600 m s −1. It is characterized by Gaussian with a maximum at about 190 m s −1 and a width at half maximum of 150 m s −1.

Properties of the dust cloud caused by the Deep Impact experiment

We present an analysis of the observations of the Deep Impact event performed by the OSIRIS narrow angle camera aboard the Rosetta spacecraft over two weeks, in an effort to characterize the cometary dust grains ejected from the nucleus of Comet 9P/Tempel 1. We adopt a Monte Carlo approach to generate calibrated synthetic images, and a linear combination of them is fitted to the calibrated images so as to determine the physical parameters of the dust cloud. Our model considers spherical olivine particles with a density of 3780 kg m −3. It incorporates constraints on the direction of the cone of emission coming from additional images obtained at Pic du Midi observatory, and constraints on the dust terminal velocities coming from the physics of the impact. We find that the slope of the differential dust size distribution of grains with radii <20 μm ( β > 0.008 ) is 3.1 ± 0.3 , a value typical of cometary dust tails. This shows that there is no evidence in our data for an enhancement in sub-micron particles in the ejecta compared to the typical dust distribution of active comets. We estimate the mass of particles with radii <1.4 μm ( β > 0.14 ) to be 1.5 ± 0.2 × 10 5 kg . These particles represent more than 80% of the cross-section of the observed dust cloud. The mass carried by larger particles depends whether the gas significantly increases the kinetic energy of the grains in the inner coma; it lies in the range 1 – 14 × 10 6 kg for particles with radii <100 μm ( β > 0.002 ). We obtain the distribution of terminal velocities reached by the dust after the dust–gas interaction which is very well constrained between 10 and 600 m s −1. It is characterized by Gaussian with a maximum at about 190 m s −1 and a width at half maximum of 150 m s −1.

The dust tail of Comet C/1999 T1 McNaught-Hartley

A numerical method to compute cometary dust tail brightnesses has been developed. The method, analogous in many ways to the inverse Monte Carlo method proposed by Fulle ([CITE]), has been applied to red continuum images of comet C/1999 T1 McNaught-Hartley obtained by Lara et al. ([CITE]). The time and size dependence of the particle terminal velocities, the size distribution functions, and the dependence with time of the power index of the size distribution have been derived. The best fits to the observed isophote fields are obtained for highly anisotropic dust grain ejection velocities. The power indexes of the time-dependent dust size distributions show small values, particularly shortly after perihelion is reached, in which a minimum of -5.5 in the power index of the size distribution function is found, suggesting the apparition of small particles. Our results are in line with previous results by Fulle ([CITE]) relating a systematic decrease of size distribution power index and dust ejection isotropy as the comet age increases. We also derived the dust mass loss rates and the quantity as a function of time, providing evidence that these two quantities do not have to be correlated if the size distribution and the dust ejection velocity are both time-dependent, in accordance with the results by Fulle ([CITE]) for comet 46/P Wirtanen.