Trajectories Of Dust Grains Research Articles

Comparison of the Eulerian and Lagrangian Approaches to Studying the Peculiarities of the Interstellar Dust Distribution in the Heliosphere in the Framework of the Cold Gas Model

Interstellar dust grains penetrate into the heliosphere (region in which the solar wind propagates) due to the relative motion of the Sun and the Local Interstellar Medium (LISM). Inside the heliosphere, the motion of dust particles is mainly governed by the electromagnetic force determined by the heliospheric magnetic field. Under the action of this force, the trajectories of dust grains experience intersections with each other and self-intersections. As a result, dust density accumulation regions appear. These regions are of a great interest in the context of theoretical studying and planning of upcoming space missions. The main aim of the present study is to model the interstellar dust distribution in the heliosphere and investigate the peculiarities of the number density distribution. To describe the dusty component, the cold gas model is used, while to compute the interstellar dust distribution two approaches are considered, namely, the Eulerian and Lagrangian approaches. For solving the continuity equation in the Lagrangian coordinates, the full Lagrangian method or the Osiptsov method is used. As a result, all the peculiarities of the dust distribution are investigated and it is found that they are located on caustics, i.e., the envelopes of interstellar dust trajectories. Besides it, the regular regions of overdensity (without singularities in the number density) are discovered. It is shown that the dust component accumulation regions are located in a small neighborhood of the heliospheric current sheet, at which the magnetic field changes its polarity, and in the tail of the heliosphere. The effectiveness of the Osiptsov method of solving the continuity equation is compared with the widely used Monte Carlo method (Eulerian approach). It is shown that Monte Carlo method requires extremely high resolution of computational grid to reach the level of accuracy comparable with the Osiptsov method.

Comparison of the Eulerian and Lagrangian Approaches to Studying the Peculiarities of the Interstellar Dust Distribution in the Heliosphere in the Framework of the Cold Gas Model

Interstellar dust grains penetrate into the heliosphere (region in which the solar wind propagates) due to the relative motion of the Sun and the Local Interstellar Medium (LISM). Inside the heliosphere, the motion of dust particles is mainly governed by the electromagnetic force determined by the heliospheric magnetic field. Under the action of this force, the trajectories of dust grains experience intersections with each other and self-intersections. As a result, dust density accumulation regions appear. These regions are of a great interest in the context of theoretical studying and planning of upcoming space missions. The main aim of the present study is to model the interstellar dust distribution in the heliosphere and investigate the peculiarities of the number density distribution. To describe the dusty component, the cold gas model is used, while to compute the interstellar dust distribution two approaches are considered, namely, the Eulerian and Lagrangian approaches. For solving the continuity equation in the Lagrangian coordinates, the full Lagrangian method or the Osiptsov method is used. As a result, all the peculiarities of the dust distribution are investigated and it is found that they are located on caustics, i.e., the envelopes of interstellar dust trajectories. Besides it, the regular regions of overdensity (without singularities in the number density) are discovered. It is shown that the dust component accumulation regions are located in a small neighborhood of the heliospheric current sheet, at which the magnetic field changes its polarity, and in the tail of the heliosphere. The effectiveness of the Osiptsov method of solving the continuity equation is compared with the widely used Monte Carlo method (Eulerian approach). It is shown that Monte Carlo method requires extremely high resolution of computational grid to reach the level of accuracy comparable with the Osiptsov method.

Motion of dust ejected from the surface of asteroid (101955) Bennu

From Jan. 6, 2019 to Feb. 18, 2019, OSIRIS-REx observed asteroid (101955) Bennu ejecting 11 plumes of dust, of which part is escaping and another part is re-captured by the asteroid. The relative magnitudes of the typical forces acting on the emitted dust are quite different from the environments of the planets and other minor planets in the solar system. Here we show that ejected dust grains from the surface of Bennu can be caught in the gravitational field of Bennu. To this end, we calculated numerically the trajectories of dust grains of various sizes, from the 0.1μm to the ten millimeter range. The shape and the fate of an emitted cloud of particles depend on the size of the grains: smaller grains form a more narrowly confined dust trail while trails formed by larger grains disperse more rapidly. Four different fates are possible for ejected dust. All grains with radius less than 1.0μm, directly re-impact on Bennu or they escape directly. In contrast, a fraction of grains with a radius larger than 10.0 μm will impact or escape only after performing a number of non-Keplerian revolutions around Bennu. Our findings show how dust grains may populate the vicinity of Bennu and other active asteroids and that they can reach interplanetary space and other celestial bodies, implying that organic matter can be transported from carbonaceous asteroids to other celestial bodies, including Earth.

The initial structure of chondrule dust rims II: Charged grains

In order to characterize the early growth of fine-grained dust rims (FGRs) that commonly surround chondrules, we simulate the growth of FGRs through direct accretion of monomers of various sizes onto the chondrule surfaces. Dust becomes charged to varying degrees in the radiative plasma environment of the solar nebula (SN), and the resulting electrostatic force alters the trajectories of colliding dust grains, influencing the structure of the dust rim as well as the time scale of rim formation. We compare the growth of FGRs in protoplanetary disks (PPD) with different turbulence strengths and plasma conditions to previous models which assumed neutral dust grains (Xiang, C., Carballido, A., Hanna, R.D., Matthews, L.S., Hyde, T.W., 2019). We use a combination of a Monte Carlo method and an N-body code to simulate the collision of dust monomers of radii 0.5–10μm with chondrules whose radii are between 500 and 1000μm: a Monte Carlo algorithm is used to randomly select dust particles that will collide with the chondrule as well as determine the elapsed time interval between collisions; at close approach, the detailed collision process is modeled using an N-body algorithm, Aggregate Builder (AB), to determine the collision outcome, as well as any restructuring of the chondrule rim. For computational expediency, we limit accretion of dust monomers to a small patch of the chondrule surface. The collisions are driven by Brownian motion and coupling to turbulent gas motion in the protoplanetary disk. The charge distribution of the dust rim is modeled, used to calculate the trajectories of dust grains, and then analyze the resulting morphology of the dust rim. In a weakly turbulent region, the decreased relative velocity between charged particles causes small grains to be repelled from the chondrule, causing dust rims to grow more slowly and be composed of larger monomers, which results in a more porous structure. In a highly turbulent region, the presence of charge mainly affects the porosity of the rim by causing dust particles to deviate from the extremities of the rim and reducing the amount of restructuring caused by high-velocity collisions.

Nonlinear Wave Structures and Plasma−Dust Effects in the Earth’s Atmosphere

The interaction of charged dust grains with nonlinear vortical structures in the Earth’s atmosphere is analyzed. Certain aspects of the atmosphere−ionosphere interaction, in particular, mechanisms for the appearance of dust grains at ionospheric altitudes, are discussed. It is shown that, at certain altitudes, there are regions in the wavenumber space in which conditions leading to the excitation of acoustic−gravity waves are satisfied. The interaction of nonlinear acoustic−gravity waves with dust grains of meteoric origin at ionospheric altitudes, which leads to the mixing and redistribution of dust grains over the region where vortices exist, is investigated. The possibility of formation of vertical and horizontal dust flows in dusty ionospheric plasma as a result of modulational instability is analyzed. The dynamics of dust grains in dust devils frequently arising in the atmosphere above well-heated surfaces is modeled. The vortical structure of such a dust devil is characterized by a reduced pressure in the center, which facilitates the lifting of small dust grains from the surface. The formulated model is used to calculate the trajectories of dust grains in dust devils with allowance for the influence of the electric field generated in the vortex by colliding dust grains. The calculations show that dust devils play an important role in the transport of dust grains.

Scientific assessment of the quality of OSIRIS images

OSIRIS, the scientific imaging system on board the ESA Rosetta spacecraft, has been imaging the nucleus of comet 67P/Churyumov-Gerasimenko and its dust and gas environment since March 2014. The images serve different scientific goals, from morphology and composition studies of the nucleus surface, to the motion and trajectories of dust grains, the general structure of the dust coma, the morphology and intensity of jets, gas distribution, mass loss, and dust and gas production rates. Aims. We present the calibration of the raw images taken by OSIRIS and address the accuracy that we can expect in our scientific results based on the accuracy of the calibration steps that we have performed. Methods. We describe the pipeline that has been developed to automatically calibrate the OSIRIS images. Through a series of steps, radiometrically calibrated and distortion corrected images are produced and can be used for scientific studies. Calibration campaigns were run on the ground before launch and throughout the years in flight to determine the parameters that are used to calibrate the images and to verify their evolution with time. We describe how these parameters were determined and we address their accuracy. Results. We provide a guideline to the level of trust that can be put into the various studies performed with OSIRIS images, based on the accuracy of the image calibration.

Investigations of the Morphology of Dust Shells of Comet C/2001 Q4 (NEAT)

The morphology of the dust fans and shells in the images of comet C/2001 Q4 (NEAT) showed significant changes between 2004 April and June due to rapid changes in the Earth viewing and solar illumination geometry. We model the trajectories of dust grains ejected from distributed sources on the comet to explain the observed dust morphology in the images obtained on 2004 April 16, May 12, 16, and 21, and June 3. From the fit to the observations we derive the direction of the rotation pole of the nucleus as αp = 270° ± 10° and δp = 15° ± 10°. The derived latitudes of the sources vary between -85° and +80°. Six of the sources are found to lie on a single meridian within ±25°. Using theoretical production rates of water from these sources, reported water production rates, and the archived visual light curve of the comet, we estimate the total active area on the comet to be 38.7 ± 5.8 km2 near perihelion. The fractional active area on the comet is 12% ± 2% or 25% ± 4% at perihelion, corresponding to a nuclear radius of 5 or 3.5 km, respectively. The large outgassing areas estimated in the present work can be attributed to the fact that comet 2001Q4 is a comet from the Oort Cloud visiting the inner solar system for the first time.

Investigations of the Rotation Pole from the Morphology of Dust Fans of Comet 81P/Wild 2

Investigations of the dust morphology of comet 81P/Wild 2 in the I- and R-band images obtained on 1997 May 15 from the Vainu Bappu Observatory, Kavalur, India, are presented. We model the trajectories of dust grains ejected from distributed sources on this comet to explain the morphology of the fans in these images and in the published images by Schulz and coworkers. We derive the pole position of αp = 297° ± 5° and δp = -10° ± 5°. Broad sources at +80° ± 5° and -25° ± 5° latitudes best explain the northern and southern fans, respectively.

A photometric-dynamic model to simulate coma and jets from a comet

A model to compute the trajectories of dust grains ejected by comets to simulate intensity and polarization maps on the sky plane is presented. The model is used to constrain the silicate to organic mass ratio, porosity and size distribution of the grains in the shells and coma of comet Hale-Bopp to explain 1) the published polarizations at three continuum wavelengths at 0.6840 μm, 0.4845 μm and 0.3650 μm at different phase angles, 2) higher polarization and bluer colour of the shells compared to the coma, 3) the intensity variation and rapid decline of polarization on the sunward side and 4) higher polarization on the anti-sunward direction. The present results obtained using Mie theory in the model indicate that although it is impossible to determine the nature of the silicate (pyroxenes/olivines or amorphous/crystalline) using the present technique, the porosity, organic fraction and size distribution of the grains can be constrained. The fit to the data set indicates an ensemble of grains in which 60% are silicate grains with a range in silicate to organic mass ratio r m between 1 and 2 and of medium porosity 8 on the shells can explain their bluer colour. A narrow size distribution between 0.08 μm-0.6 μm is inferred for 70% of the grains in the coma and shell. These small grains may not be individual grains but part of loosely bound grains in which larger grains may also be present which may control the dynamics. The narrow size distribution may therefore represent statistically the size range of individual subunits of larger highly porous aggregates of fractal dimension close to two. The polarizations in JHK bands also support the aggregate structure. Despite the availability of an extensive and wide range of data set on this comet, the inclusion of a large parameter space, lack of knowledge on the nature of organic material found in comets and use of Mie theory, which does not adequately represent the polarization phase curves of natural grains, set limitations in getting a unique solution in the present work. The results presented here are open to improvements when more realistic light scattering theories are used in the model and our understanding on the nature of the organic content of the grains improves. However, visibility of up to 8-10 shells in well exposed images implies β < 1 for these grains. As a result of this dynamical constraint which is independent of the assumptions on the scattering characteristics of the grains, the results for the dust grains in the shell may be more robust compared to that of the coma.

Dust Cloud near the Sun

General structure and composition of the near-solar dust cloud are investigated. Based on estimates for sources and transport of dust to the near-solar region, we derive a representative set of trajectories of dust grains by numerical integrations and obtain the spatial distribution of different dust populations within 10 solar radii ( R ⊙) from the Sun. For the radial structure, we find the dust number density to be enhanced by a factor of 1 to 4 in a typical heliocentric distance zone with a width of 0.2 R ⊙ in the sublimation region—the formation of a dust ring—depending on the materials and porosities considered. The excess density in the ring increases with increasing initial size for porous grains and decreases for compact ones. Non-zero eccentricities of the dust orbits decrease the enhancement. Moderate enhancements that we predict are consistent with eclipse observations, most of which have not shown any peak features in the F-corona brightness at several solar radii. We describe typical features of β-meteoroids formed by the sublimation of particles near the Sun and estimate the total mass loss due to this mechanism to range between 1 and 10 kg s −1. For the vertical structure of the dust cloud we show that grains larger than ∼10 μm in size keep in a disk with a typical thickness of tens degrees; grains with radii of several μm fill in a broader disk-like volume which is tilted off the ecliptic plane by a variable angle depending on the solar activity cycle; submicrometer-sized grains form a nearly spherical halo around the Sun with a radius of more than 10 R ⊙. From our present knowledge we cannot exclude the existence of an additional spheroidal component of larger grains near the Sun, which depends on how effective long-period comets are as sources of dust. Estimates of absolute number densities and local fluxes of dust show that simple extrapolation of the interplanetary dust cloud into the solar vicinity does not describe the dust cloud near the Sun properly. A complex latitudinal dependence of the fluxes of micrometer-sized grains, as well as variability of these fluxes with the solar activity phase, are predicted. The fluxes and their time variations depend on the physical and chemical properties of dust.