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Author name code: zakharov
ADS astronomy entries on 2022-09-14
=author:"Zakharov, V.V."
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Title: Comets beyond 4 au: How pristine are Oort nuclei?
Authors: Fulle, Marco; Lazzarin, M.; La Forgia, F.; Zakharov, V. V.;
Bertini, I.; Mazzotta Epifani, E.; Ammannito, E.; Buzzoni, A.; Capria,
M. T.; Carbognani, A.; Da Deppo, V.; Della Corte, V.; Fiscale, S.;
Frattin, E.; Inno, L.; Migliorini, A.; Pernechele, C.; Rotundi, A.;
Sindoni, G.; Tubiana, C.; Milani, G.; Aletti, A.; Bacci, P.; Baj, G.;
Bellini, F.; Bryssinck, E.; Di Grazia, M.; Facchini, M.; Feraco, M.;
Guido, E.; Ligustri, R.; Kugel, F.; Maestripieri, M.; Tirelli, D.;
Valvasori, A.; Snodgrass, C.; Jones, G. H.
2022MNRAS.513.5377F Altcode:
The ESA mission Comet Interceptor will target an Oort or interstellar
comet during its first approach to the Sun. Meanwhile, the Vera
Rubin LSST Survey will observe hundreds of active comets per month
beyond 4 au from the Sun, where water vapour pressure is expected
to be too low to eject dust. We discuss observations of dust tails
at heliocentric distances larger than 4 au in order to retrieve the
physical parameters driving cometary activity beyond Jupiter by means
of a probabilistic tail model, which is consistent with the activity
model defining the gas coma parameters due to the sublimation of carbon
monoxide, molecular oxygen, methane, ethane, and carbon dioxide since
the activity onset at 85 au from the Sun. We find that: (i) All the
observed dust tails are consistent with the adopted activity model;
(ii) The tail fits depend on three free parameters only, all correlated
to the nucleus size; (iii) Tail fits are always improved by anisotropic
dust ejection, suggesting activity of Oort nuclei dominated by seasons;
(iv) Inbound seasons suggest cometary activity before the ejection of
protocomets into the Oort cloud, as predicted by the activity model;
(v) Oort nuclei larger than 1 km may be characterized by a fallout
up to ≍100 m thick deposited during ≍60 yr inbound; (vi) On the
other side, Oort nuclei smaller than 1 km may appear more pristine
than Jupiter Family Comets when observed at 1 au from the Sun.
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Title: On the similarity of dust flows in the inner coma of comets
Authors: Zakharov, V. V.; Rotundi, A.; Della Corte, V.; Fulle, M.;
Ivanovski, S. L.; Rodionov, A. V.; Bykov, N. Y.
2021Icar..36414476Z Altcode:
The atmosphere of a comet is formed by the sublimation, due to solar
illumination, of its volatile component and the dust particles ejected
from its nucleus and entrained by the gas flow. Contemporary dusty-gas
coma models take into account numerous physical processes occurring in
the coma and a complex geometry of the nucleus. For the description
of the dusty-gas flow in the coma, such models introduce a large
number of governing parameters characterizing physical properties
and processes. The relative role of these processes is not easy
to ascribe therefore a relevant inter-comparison of model results
becomes difficult. <P />The present work introduces a set of universal,
dimensionless parameters, which characterize the dust motion in the
inner cometary coma. This approach allows one to: (i) reduce the number
of parameters for analysis; (ii) reveal dust flows similarities; (iii)
rescale the available numerical solutions. The present work demonstrates
application of this approach to a realistic coma model. <P />Description
of dust motion with dimensionless parameters allows us to make a
parametric study for a broad range of conditions and to find simple
analytic approximations (via a polynomial function) of the numerical
results suitable for rough estimations of dust density in the coma.
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Title: Observational constraints to the dynamics of dust particles
in the coma of comet 67P/Churyumov-Gerasimenko
Authors: Frattin, E.; Bertini, I.; Ivanovski, S. L.; Marzari, F.;
Fulle, M.; Zakharov, V. V.; Moreno, F.; Naletto, G.; Lazzarin, M.;
Cambianica, P.; Cremonese, G.; Ferrari, S.; Ferri, F.; Güttler, C.;
La Forgia, F.; Lucchetti, A.; Pajola, M.; Penasa, L.; Rotundi, A.;
Sierks, H.; Tubiana, C.
2021MNRAS.504.4687F Altcode: 2021arXiv210410950F; 2021MNRAS.tmp.1157F
In this work, we aim to characterize the dust motion in the inner
coma of comet 67P/Churyumov-Gerasimenko to provide constraints for
theoretical 3D coma models. The OSIRIS camera on-board the Rosetta
mission was able for the first time to acquire images of single dust
particles from inside the cometary coma, very close to the nucleus. We
analyse a large number of particles, performing a significant
statistic of their behaviour during the post-perihelion period, when
the spacecraft covered distances from the nucleus ranging between
80 and 400 km. We describe the particle trajectories, investigating
their orientation and finding highly radial motion with respect to
the nucleus. Then, from the particle brightness profiles, we derive a
particle rotational frequency of ν < 3.6 Hz, revealing that they
are slow rotators and do not undergo fragmentation. We use scattering
models to compare the observed spectral radiance of the particles with
the simulated ones in order to estimate their size, finding values that
range from millimetres up to centimetres. The statistics performed in
this paper provide useful parameters to constrain the cometary coma
dynamical models.
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Title: Practical relations for assessments of the gas coma parameters
Authors: Zakharov, V. V.; Rodionov, A. V.; Fulle, M.; Ivanovski,
S. L.; Bykov, N. Y.; Della Corte, V.; Rotundi, A.
2021Icar..35414091Z Altcode:
To ensure the safety of a spacecraft and efficiency of the instrument
operations it is indispensable to have simple (i.e. with minimal
number of parameters and which does not require long time simulations)
models for the assessments of the dusty-gas coma. A dusty-gas flow
from cometary nucleus preserves common general structure regardless
the features of a particular comet. Therefore, elementary models which
account only for the main factors affecting the dusty-gas motion could
be used for rough estimations of such characteristics and asymptotic
behavior of dusty-gas motion. <P />In a wide range of conditions a
presence of dust in the coma does not affect the gas motion. Therefore,
it is possible to study the dynamics of a gas environment separately,
without taking into account the dust. The present work is devoted
to the gas environment of the comet. The main goal of the work is to
develop a simplified model of gas environment which allows to estimate
spatial distribution of gas parameters in the coma in the range of
nucleus-centric distances from ten to thousand radius of the nucleus.
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Title: Experimental Phase Function and Degree of Linear Polarization
Curves of Millimeter-sized Cosmic Dust Analogs
Authors: Muñoz, O.; Moreno, F.; Gómez-Martín, J. C.; Vargas-Martín,
F.; Guirado, D.; Ramos, J. L.; Bustamante, I.; Bertini, I.; Frattin,
E.; Markannen, J.; Tubiana, C.; Fulle, M.; Güttler, C.; Sierks,
H.; Rotundi, A.; Della Corte, V.; Ivanovski, S.; Zakharov, V. V.;
Bockelée-Morvan, D.; Blum, J.; Merouane, S.; Levasseur-Regourd,
A. C.; Kolokolova, L.; Jardiel, T.; Caballero, A. C.
2020ApJS..247...19M Altcode:
We present laboratory measurements of the phase functions and degree of
linear polarization (DLP) curves of a selection of millimeter-sized
cosmic dust analog particles. The set includes particles with
similar sizes but diverse internal structure (compact and porous) and
absorbing properties. The measured phase functions are found to be in
all cases very different from those of micron-sized particles. They
show a monotonic decrease with increasing phase angle from the back-
to the side-scattering region, reaching a minimum at large phase
angles before a steep increase of the forward peak. This is in stark
contrast to the phase functions of micron-sized particles, which are
rather flat at low and intermediate phase angles. The maximum of the
DLP for millimeter-sized compact particles is shifted toward larger
phase angles (∼130°) compared to that of micron-sized particles
(∼90°). Porosity plays an important role in the measured DLP
curves: the maximum significantly decreases for increasing porosity
as a result of multiple scattering within the particle. Large porous
particles with highly absorbing inclusions can reproduce both the
OSIRIS/Rosetta phase functions and ground-based DLP observations of
comet 67P/Churyumov-Gerasimenko.
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Title: Models of Rosetta/OSIRIS 67P Dust Coma Phase Function
Authors: Moreno, F.; Guirado, D.; Muñoz, O.; Bertini, I.; Tubiana,
C.; Güttler, C.; Fulle, M.; Rotundi, A.; Della Corte, V.; Ivanovski,
S. L.; Rinaldi, G.; Bockelée-Morvan, D.; Zakharov, V. V.; Agarwal,
J.; Mottola, S.; Toth, I.; Frattin, E.; Lara, L. M.; Gutiérrez,
P. J.; Lin, Z. Y.; Kolokolova, L.; Sierks, H.; Naletto, G.; Lamy,
P. L.; Rodrigo, R.; Koschny, D.; Davidsson, B.; Barucci, M. A.;
Bertaux, J. -L.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei,
S.; De Cecco, M.; Deller, J.; Fornasier, S.; Ip, W. -H.; Keller,
H. U.; Lazzarin, M.; López-Moreno, J. J.; Marzari, F.; Shi, X.
2018AJ....156..237M Altcode: 2018arXiv180910424M
The phase function of the dust coma of comet 67P has been determined
from Rosetta/OSIRIS images. This function shows a deep minimum at phase
angles near 100°, and a strong backscattering enhancement. These
two properties cannot be reproduced by regular models of cometary
dust, most of them based on wavelength-sized and randomly oriented
aggregate particles. We show, however, that an ensemble of oriented
elongated particles of a wide variety of aspect ratios, with radii
r ≳ 10 μm, and whose long axes are perpendicular to the direction
of the solar radiation, are capable of reproducing the observed phase
function. These particles must be absorbing, with an imaginary part
of the refractive index of about 0.1 to match the expected geometric
albedo, and with porosity in the 60%-70% range.
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Title: The near-nucleus gas coma of comet 67P/Churyumov-Gerasimenko
prior to the descent of the surface lander PHILAE
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.; Rubin, M.;
Altwegg, K.
2018A&A...618A..71Z Altcode:
Context. The European Space Agency (ESA) Rosetta mission was the
most comprehensive study of a comet ever performed. In particular,
the Rosetta orbiter, which carried many instruments for monitoring the
evolution of the dusty gas emitted by the cometary nucleus, returned
an enormous volume of observational data collected from the close
vicinity of the nucleus of comet 67P/Churyumov-Gerasimenko. <BR />
Aims: Such data are expected to yield unique information on the physical
processes of gas and dust emission, using current physical model fits
to the data. We present such a model (the RZC model) and our procedure
of adjustment of this model to the data. <BR /> Methods: The RZC
model consists of two components: (1) a numerical three-dimensional
time-dependent code solving the Eulerian/Navier-Stokes equations
governing the gas outflow, and a direct simulation Monte Carlo (DSMC)
gaskinetic code with the same objective; and (2) an iterative procedure
to adjust the assumed model parameters to best-fit the observational
data at all times. <BR /> Results: We demonstrate that our model is
able to reproduce the overall features of the local neutral number
density and composition measurements of Rosetta Orbiter Spectrometer
for Ion and Neutral Analysis (ROSINA) Comet Pressure Sensor (COPS)
and Double Focusing Mass Spectrometer (DFMS) instruments in the period
August 1-November 30, 2014. The results of numerical simulations
show that illumination conditions on the nucleus are the main driver
for the gas activity of the comet. We present the distribution of
surface inhomogeneity best-fitted to the ROSINA COPS and DFMS in
situ measurements.
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Title: Asymptotics for spherical particle motion in a spherically
expanding flow
Authors: Zakharov, V. V.; Ivanovski, S. L.; Crifo, J. -F.; Della Corte,
V.; Rotundi, A.; Fulle, M.
2018Icar..312..121Z Altcode:
In the context of an increasing number of complex multiparametric
dust coma models it was found convenient to construct an elementary
model with a minimum number of parameters selected to represent the
key processes acting on the dust. The models outputs can be used
as a reference evaluation of these processes with rough estimates
of the resulting dust properties e.g. velocity. <P />The present
work introduces three, universal, dimensionless parameters which
characterize the dust motion in an expanding flow, and computes as
a function of these parameters the dust terminal velocity, the time
it takes to acquire it, and the distance at which it is acquired. <P
/>The motion of dust grains is presented as a system of dimensionless
ordinary differential equations the solution of which depends upon the
above mentioned three parameters. The numerical integration of this
system was performed over a wide range of parameter space covering the
whole range of physically possible conditions. <P />Precomputed results
of dust terminal velocity, time and distance where it is reached are
presented in dimensionless form. To obtain dimensional values for a
particular case it is sufficient to perform algebraic operations.
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Title: The Near-Nucleus Dusty Gas Coma of Comet 67P Prior to the
Descent of PHILAE
Authors: Zakharov, V. V.; Marzari, F.; Crifo, J. -F.; Bertini, I.;
Rodionov, A. V.; Fulle, M.
2017EPSC...11..683Z Altcode:
We here describe the RZC model developed to predict the gas environment
of the comet 67P (it was used for estimation of the aerodynamic forces
on the Rosetta lander in November 2014) and the results of adjustment
of this model to the observational data obtained by the Rosetta probe
before landing. We outline the physical approach adopted to overcome the
difficulties resulting from (1) the extreme complexity of the nucleus
surface, (2) the absence of direct measurements of the gas flux at
the surface itself, (3) the time-dependence of the gas production
induced by the fast nucleus rotation. Also, we present the results
of our attempts to fit the dust coma images obtained by the Optical,
Spectroscopic, and Infrared Remote Imaging System (OSIRIS).
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Title: Dynamics of aspherical dust grains in a cometary atmosphere:
I. axially symmetric grains in a spherically symmetric atmosphere
Authors: Ivanovski, S. L.; Zakharov, V. V.; Della Corte, V.; Crifo,
J. -F.; Rotundi, A.; Fulle, M.
2017Icar..282..333I Altcode:
In-situ measurements of individual dust grain parameters in the
immediate vicinity of a cometary nucleus are being carried by the
Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. For the
interpretations of these observational data, a model of dust grain
motion as realistic as possible is requested. In particular, the results
of the Stardust mission and analysis of samples of interplanetary dust
have shown that these particles are highly aspherical, which should
be taken into account in any credible model. The aim of the present
work is to study the dynamics of ellipsoidal shape particles with
various aspect ratios introduced in a spherically symmetric expanding
gas flow and to reveal the possible differences in dynamics between
spherical and aspherical particles. Their translational and rotational
motion under influence of the gravity and of the aerodynamic force and
torque is numerically integrated in a wide range of physical parameters
values including those of comet 67P/Churyumov-Gerasimenko. The main
distinctions of the dynamics of spherical and ellipsoidal particles
are discussed. The aerodynamic characteristics of the ellipsoidal
particles, and examples of their translational and rotational motion
in the postulated gas flow are presented.
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Title: The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta
multi-instrument study
Authors: Grün, E.; Agarwal, J.; Altobelli, N.; Altwegg, K.;
Bentley, M. S.; Biver, N.; Della Corte, V.; Edberg, N.; Feldman,
P. D.; Galand, M.; Geiger, B.; Götz, C.; Grieger, B.; Güttler, C.;
Henri, P.; Hofstadter, M.; Horanyi, M.; Jehin, E.; Krüger, H.; Lee,
S.; Mannel, T.; Morales, E.; Mousis, O.; Müller, M.; Opitom, C.;
Rotundi, A.; Schmied, R.; Schmidt, F.; Sierks, H.; Snodgrass, C.;
Soja, R. H.; Sommer, M.; Srama, R.; Tzou, C. -Y.; Vincent, J. -B.;
Yanamandra-Fisher, P.; A'Hearn, M. F.; Erikson, A. I.; Barbieri, C.;
Barucci, M. A.; Bertaux, J. -L.; Bertini, I.; Burch, J.; Colangeli,
L.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco,
M.; Deller, J.; Feaga, L. M.; Ferrari, M.; Fornasier, S.; Fulle,
M.; Gicquel, A.; Gillon, M.; Green, S. F.; Groussin, O.; Gutiérrez,
P. J.; Hofmann, M.; Hviid, S. F.; Ip, W. -H.; Ivanovski, S.; Jorda,
L.; Keller, H. U.; Knight, M. M.; Knollenberg, J.; Koschny, D.; Kramm,
J. -R.; Kührt, E.; Küppers, M.; Lamy, P. L.; Lara, L. M.; Lazzarin,
M.; Lòpez-Moreno, J. J.; Manfroid, J.; Epifani, E. Mazzotta; Marzari,
F.; Naletto, G.; Oklay, N.; Palumbo, P.; Parker, J. Wm.; Rickman,
H.; Rodrigo, R.; Rodrìguez, J.; Schindhelm, R.; Shi, X.; Sordini,
R.; Steffl, A. J.; Stern, S. A.; Thomas, N.; Tubiana, C.; Weaver,
H. A.; Weissman, P.; Zakharov, V. V.; Taylor, M. G. G. T.
2016MNRAS.462S.220G Altcode: 2016MNRAS.tmp.1212G
On 2016 Feb 19, nine Rosetta instruments serendipitously
observed an outburst of gas and dust from the nucleus of comet
67P/Churyumov-Gerasimenko. Among these instruments were cameras and
spectrometers ranging from UV over visible to microwave wavelengths,
in situ gas, dust and plasma instruments, and one dust collector. At
09:40 a dust cloud developed at the edge of an image in the shadowed
region of the nucleus. Over the next two hours the instruments
recorded a signature of the outburst that significantly exceeded the
background. The enhancement ranged from 50 per cent of the neutral gas
density at Rosetta to factors >100 of the brightness of the coma
near the nucleus. Dust related phenomena (dust counts or brightness
due to illuminated dust) showed the strongest enhancements (factors
>10). However, even the electron density at Rosetta increased by
a factor 3 and consequently the spacecraft potential changed from
∼-16 V to -20 V during the outburst. A clear sequence of events
was observed at the distance of Rosetta (34 km from the nucleus):
within 15 min the Star Tracker camera detected fast particles (∼25
m s<SUP>-1</SUP>) while 100 μm radius particles were detected by the
GIADA dust instrument ∼1 h later at a speed of 6 m s<SUP>-1</SUP>. The
slowest were individual mm to cm sized grains observed by the OSIRIS
cameras. Although the outburst originated just outside the FOV of the
instruments, the source region and the magnitude of the outburst could
be determined.
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Title: 3D numerical simulations of radiative transfer in the
cometary coma
Authors: Zakharov, V. V.; Crifo, J. -F.; Bockelée-Morvan, D.;
Biver, N.
2013EPSC....8..719Z Altcode:
We report about the resent advances in the development of our 3D model
of water excitation in cometary atmosphere in which radiation transfer
is treated on the base of the accelerated Monte Carlo method.
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Title: 3D+t Mathematical Simulation of the Dusty-Gas Cometary
Atmosphere (Application to the Comet 103P/ Hartley 2)
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.
2012epsc.conf..678Z Altcode: 2012espc.conf..678Z
We report the results of application of our 3D+t dustgas coma model to a
model nucleus which shape and dimensions close to those of 103P/Hartley
2 nucleus and conditions at the moment of closest approach i.e. at
13:59:47.31 UTC on 4 November 2010 (1.064 AU from the Sun). We assume
various cases of gas and dust production of the nucleus taking into
account available observational data.
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Title: Dynamics of aspherical dust for the GIADA experiment in the
coma of 67P/Churyumov- Gerasimenko: I. Comparison with the spherical
approximation
Authors: Ivanovski, S. L.; Zakharov, V. V.; Crifo, J. -F.; Della Corte,
V.; Fulle, M.; Rotundi, A.
2012epsc.conf..592I Altcode: 2012espc.conf..592I
We report the recent advances in developing of the model of aspherical
dust grain dynamics [1] in the cometary atmosphere of 67P/Churyumov-
Gerasimenko. The present model is aimed to support the scientific
objectives of GIADA in-situ experiment [2] on board of the ESA ROSETTA
probe and will provide predictions on the real dust cometary grains. The
currently used 3D+t models [3, 4] assume sphericity of the grains but
the dynamics of aspherical grains can be very different from spherical
[5].At this stage we study grains moving under the influence of two
forces: aerodynamic and gravitational and discuss the distinctions
between the aspherical and the spherical approximations.
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Title: Investigation of dust and water ice in comet 9P/Tempel 1 from
Spitzer observations of the Deep Impact event
Authors: Gicquel, A.; Bockelée-Morvan, D.; Zakharov, V. V.; Kelley,
M. S.; Woodward, C. E.; Wooden, D. H.
2012A&A...542A.119G Altcode:
Context. The Spitzer spacecraft monitored the Deep Impact event on
2005 July 4 providing unique infrared spectrophotometric data that
enabled exploration of comet 9P/Tempel 1's activity and coma properties
prior to and after the collision of the impactor. <BR /> Aims: The
time series of spectra take with the Spitzer Infrared Spectrograph
(IRS) show fluorescence emission of the H<SUB>2</SUB>O ν<SUB>2</SUB>
band at 6.4 μm superimposed on the dust thermal continuum. These
data provide constraints on the properties of the dust ejecta cloud
(dust size distribution, velocity, and mass), as well as on the water
component (origin and mass). Our goal is to determine the dust-to-ice
ratio of the material ejected from the impact site. <BR /> Methods: The
temporal evolution of the continuum was analyzed using a dust thermal
model which considers amorphous carbon and intimate silicate-carbon
mixtures. The water emission was extracted from the spectra and the
water columns within the Spitzer extraction aperture were inferred
using a fluorescence excitation model. Time-dependent models simulating
the development of the ejecta cloud and the sublimation of icy grains
were developed to interpret the temporal evolution of both dust and
water emissions within the field of view. <BR /> Results: Both the
color temperature of the grains in the ejecta cloud (375 ± 5 K)
and their size distribution show that a large quantity of submicron
grains were ejected by the impact. The velocity of the smallest grains
is 230 m s<SUP>-1</SUP>, with a power index for the size dependence
of 0.3-0.5, in agreement with gas loading. The total mass of dust is
(0.7-1.2) × 10<SUP>5</SUP> kg for grain sizes 0.1-1 μm and (0.5-2.1)
× 10<SUP>6</SUP> kg for sizes 0.1-100 μm. A sustained production
of water is observed, which can be explained by the sublimation of
pure ice grains with sizes less than 1 μm and comprising a mass
of ice of (0.8-1.8) × 10<SUP>7</SUP> kg. The contribution of dirty
ice grains to the ice budget is negligible. Assuming that water was
essentially produced by icy grains present in the ejecta cloud, our
measurements suggest a very high ice-to-dust ratio of about 10 in the
excavated material, which greatly exceeds the gas-to-dust production
rate ratio of ~0.5 measured for the background coma. Alternately, if
a large amount of material felt back to the surface and sublimated,
ice-to-dust ratios of 1-3 are not excluded. A better understanding of
the cratering event on 9P/Tempel 1 is required to disentangle between
the two hypotheses. Evidence for grain fragmentation in the ejecta
cloud is found in the data. The pre-impact water production rate is
measured to be (4.7 ± 0.7) × 10<SUP>27</SUP> mol s<SUP>-1</SUP>.
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Title: Model of Aspherical Dust Dynamics for GIADA Experiment in the
Coma of 67P/Churyumov-Gerasimenko: I. Comparison with the Spherical
Approximation
Authors: Ivanovski, S. L.; Zakharov, V. V.; Crifo, J. F.; Della Corte,
V.; Rotundi, A.; Fulle, M.
2012LPICo1667.6444I Altcode:
We report the recent advances in developing of the model of aspherical
dust grain dynamics in the cometary atmosphere for GIADA experiment
on a board of ROSETTA orbiter. We discuss its distinctions from the
spherical grain model.
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Title: Mathematical Simulation of the 3D+t Dusty-Gas Cometary
Atmosphere of Comet 103P/ Hartley 2
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.
2012LPICo1667.6401Z Altcode:
We report the results of application of our 3D+t dust-gas coma
model to a model nucleus which shape and dimensions close to those of
103P/Hartley 2 nucleus and conditions at the moment of closest approach
in EPOXI mission.
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Title: Pure ice grains in the coma of 9P/Tempel 1 after Deep Impact
Authors: Gicquel, A.; Bockelée-Morvan, D.; Zakharov, V. V.; Kelley,
M. S.; Woodward, C. E.; Wooden, D. H.
2011epsc.conf..233G Altcode: 2011DPS....43..233G
The Deep Impact (DI) spacecraft encountered comet 9P/Tempel 1 on July
4th, 2005. The spacecraft released an impactor that collided with the
comet nucleus and excavated (possibly unprocessed) cometary material
in a prominent ejecta plume. We report on the temporal evolution
of water molecules observed with the IRS instrument on the Spitzer
Space telescope after impact. We show that it can only be explained
by the presence of subliming pure ice grains. The mass of water ice
in subliming 0.1 - 1 μm grains is close to 2 x 106 kg.
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Title: A numerical study of the dusty-gas atmosphere of comet
67P/Churyumov-Gerasimenko
Authors: Zakharov, V. V.; Rodionov, A. V.; Crifo, J. -F.; Fulle, M.
2011epsc.conf..126Z Altcode: 2011DPS....43..126Z
We apply out 3D+t model to study the influence of H2O and CO production
and its nonuniformity on the gas and dust dynamics in the vicinity of
a rotating three-dimensional nucleus. The parameters of simulations
correspond to the conditions of the rendezvous of the Rosetta probe
with the comet 67P/Churyumov-Gerasimenko. We assume various models of
gas and dust production of the nucleus taking into account available
VLT observations. We present also the estimations of aerodynamic forces
and dust contamination of the Rosetta orbiter and the lander.
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Title: Monte-Carlo and multifluid modelling of the circumnuclear dust
coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei
Authors: Zakharov, V. V.; Rodionov, A. V.; Lukianov, G. A.; Crifo,
J. F.
2009Icar..201..358Z Altcode:
We use our newly developed Dust Monte-Carlo (DMC) simulation technique
[Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V.,
2005. Icarus 176, 192-219] to study the dynamics of dust grains in
the vicinity of some of the benchmark aspherical, homogeneous cometary
nuclei and of the benchmark spherical, inhomogeneous nuclei studied by
us precedingly. We use the interim unrealistic simplifying assumptions
of grain sphericity, negligible nucleus rotation rate, and negligible
tidal force, but take accurately into account the nucleus gravitational
force, gas coma aerodynamic force, and solar radiation pressure force,
and consider the full mass range of ejectable spherical grains. The
resulting complicated grain motions are described in detail, as well
as the resulting complicated and often counter-intuitive dust coma
structure. The results are used to answer several important questions:
(1) When computing coma dust distributions, (a) is it acceptable to
take into consideration only one or two of the above mentioned forces
(as currently done)? (b) to which accuracy must these forces be known,
in particular is it acceptable to represent the gravity of an aspherical
nucleus by a spherically symmetric gravity? (c) how do the more
efficient but less general Dust Multi-Fluid (DMF) computations compare
with the DMC results? (2) Are there simple structural relationships
between the dust coma of a nucleus at small heliocentric distance r, and
that of the same nucleus at large r? (3) Are there similarities between
the gas coma structures and the associated dust coma structures? (4)
Are there dust coma signatures revealing non-ambiguously a spherical
nucleus inhomogeneity or an homogeneous nucleus asphericity? (5)
What are the implications of the apparently quite general process of
grain fall-backs for the evolution of the nucleus surface, and for
the survival of a landed probe?
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Title: Navier Stokes and direct Monte-Carlo simulations of the
circumnuclear gas coma. III. Spherical, inhomogeneous sources
Authors: Zakharov, V. V.; Rodionov, A. V.; Lukyanov, G. A.; Crifo,
J. F.
2008Icar..194..327Z Altcode:
We pursue our program of comparative simulations of the cometary
gas coma by the two most advanced techniques available: (1) numerical
solution of Navier-Stokes equations coupled to the Boltzman equation in
the surface boundary layer, and (2) direct Monte-Carlo simulation. Here,
we consider two different spherical but compositionally inhomogeneous
nuclei, at three very different levels of gas production. The results
show the same excellent agreement between the two methods in a domain
adjacent to the surface as found precedingly, practically down to
free-molecular conditions. A wealth of coma density patterns with
non-intuitive structure is obtained. Some of these structures appear
even under free-molecular effusion from the surface. The physical origin
of all structures is discussed, and their evolution with changing
gas production is studied. The computed comae are compared to those
computed by various authors precedingly. Intercomparison of the present
results demonstrates that differing inhomogeneity patterns may lead to
similar structures in the gas coma. Comparison between these structures
and those created by homogeneous, aspherical surfaces shows that it
is not possible to guess from empirical rules which one of the two
processes is responsible for the creation of a given structure. The
implications for the interpretation of future high resolution images,
or of future in situ mass spectrometric samplings of the near-nucleus
gas coma are discussed.
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Title: Monte-Carlo Modelling of the Circumnuclear Dust Coma: Benchmark
Aspherical-Homogeneous and Spherical-Inhomogeneous Nuclei
Authors: Zakharov, V. V.; Crifo, J. F.; Lukianov, G. A.; Rodionov,
A. V.
2008LPICo1405.8148Z Altcode:
No abstract at ADS
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Title: Numerical Simulations of Water Spectra Obtained with the
Microwave Instrument for the Rosetta Orbiter (MIRO) from Comet
67P/Churyumov-Gerasimenko
Authors: Zakharov, V. V.; Bockelée-Morvan, D.; Biver, N.; Crovisier,
J.; Crifo, J. F.; Gulkis, S.; Rodionov, A. V.
2008LPICo1405.8144Z Altcode:
No abstract at ADS
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Title: High-resolution CN spectroscopy of small-scale solar magnetic
features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2007msfa.conf..161Z Altcode:
High-resolution spectroscopic observations of small-scale magnetic
elements in the solar photosphere were carried out in the spectral
region 387.5388.4 nm with the 1-m Swedish Solar Telescope (SST). This
part of the spectrum covers not only the violet CN band-head, but also
contains some lines of the CH molecule. The analysis of the line-core
intensity contrasts of the CN and CH lines in bright points (BPs)
yielded that on average the BPs appear brighter, thus providing a higher
rms contrast, in the CN than in the CH lines in the same spectral band.
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Title: High-Resolution CN Spectroscopy of Small-Scale Solar Magnetic
Features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2006IAUJD...3E..87Z Altcode:
High-resolution spectroscopic observations of the Sun have been
carried out with the TRIPPEL spectrograph installed at the new 1-m
Swedish Solar Telescope (SST) using realtime AO correction. A detailed
spectroscopic analysis of individual photospheric bright points (BP)
and faculae-like structures simultaneously in two spectral domains,
i.e 387.588<λ<388.473 nm (violet CN band) and in a blue spectral
band at 436.1<λ<436.9 nm, containing absorption lines of CH,
obtained at the disc center and near the limb is presented. The
estimated spatial resolution of the obtained spectra is around
0.25 arcsec while the spectral resolving power is around 130.000
in the first domain, and 76.000 in the second spectral region,
respectivlely. The first spectral band covers absorption lines of
both, CH and CN molecules, as well as many atomic lines. This enabled
us to make a quantitative comparison of their absorption and Doppler
shifts in the different photospheric features. The absorption lines
of the CN molecule and many atoms are depressed in a BP's interior
with respect to those in the quiet Sun. Our quantitative comparison
of the relative line depression of CH lines with respect to CN lines
showed that the latter have weaker absorption by a factor of 1.28 at
the disc centre and 1.32 near the limb. The CN line-core intensity,
at the disc centre, has higher BP contrast than the contrast in the
CH line-core by a factor of 1.9, and the ratio of these contrasts
is decreasing with increasing continuum intensity of the BPs. This
trend is similar to that obtained from previous simultaneous G-band
and violet CN-band imaging observations. Measurements of contrasts and
rms contrasts of line-core, integrated and local continuum intensities
are provided. Analysis of Doppler shifts and line broadening of an
Fe I line at 387.777 nm revealed an increase of the FWHM in the BP's
interior and in dark intergranular lanes and a decrease with increasing
intensity of the granules. The first results of a direct comparison
of observed CN spectra with those simulated in MHD models in different
photospheric features is presented.
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Title: A new approach for modeling the dust dynamics in the
near-nucleus coma
Authors: Lukyanov, G. A.; Crifo, J. F.; Zakharov, V. V.; Rodionov,
A. V.
2006AdSpR..38.1976L Altcode:
We describe the first step of development of a most general code for
the investigation of the dust dynamics inside the gas-dust interaction
region surrounding an active cometary nucleus. The code is based on a
Monte Carlo approach, which allows (a) consideration of realistic, i.e.,
extremely complicated assumptions with respect to the dust and nucleus
size, shape and composition, (b) the derivation of the dust velocity
distribution at each point, an information needed for the analysis of
future in situ dust samplings, and (c) allowance for all the forces
acting on the grains, i.e., aerodynamical, gravitational, radiative
and inertial. In the present first step, the trivial (unrealistic)
assumptions of nucleus and dust grain homogeneity and sphericity are
still made, and only the nucleus gravity, the aerodynamic force and
the radiation pressure force are considered. The code was tested
assuming a Halley-like grain mass distribution extending from 10
<SUP>-18</SUP> to 10 <SUP>-2</SUP> g, and nucleus H <SUB>2</SUB>O
sublimation rates from 3 × 10 <SUP>26</SUP> to 3 × 10 <SUP>28</SUP>
molecule/s. The results demonstrate that (1) even in this simple case,
none of the preceding forces can be a priori neglected; (2) due to
the combined action of these forces, a wealth of currently overlooked
complex grain trajectories exist. These results are compared to the
previously developed dust multi-fluid (DMF) method, thus evidencing
the relative capabilities of the two methods.
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Title: Direct Monte Carlo and multifluid modeling of the circumnuclear
dust coma. Spherical grain dynamics revisited
Authors: Crifo, J. -F.; Loukianov, G. A.; Rodionov, A. V.; Zakharov,
V. V.
2005Icar..176..192C Altcode:
This paper describes the first computations of dust distributions in
the vicinity of an active cometary nucleus, using a multidimensional
Direct Simulation Monte Carlo Method (DSMC). The physical model is
simplistic: spherical grains of a broad range of sizes are liberated
by H <SUB>2</SUB>O sublimation from a selection of nonrotating sunlit
spherical nuclei, and submitted to the nucleus gravity, the gas drag,
and the solar radiation pressure. The results are compared to those
obtained by the previously described Dust Multi-Fluid Method (DMF)
and demonstrate an excellent agreement in the regions where the DMF
is usable. Most importantly, the DSMC allows the discovery of hitherto
unsuspected dust coma properties in those cases which cannot be treated
by the DMF. This leads to a thorough reconsideration of the properties
of the near-nucleus dust dynamics. In particular, the results show that
(1) none of the three forces considered here can be neglected a priori,
in particular not the radiation pressure; (2) hitherto unsuspected
new families of grain trajectories exist, for instance trajectories
leading from the nightside surface to the dayside coma; (3) a wealth
of balistic-like trajectories leading from one point of the surface
to another point exist; on the dayside, such trajectories lead to
the formation of "mini-volcanoes." The present model and results
are discussed carefully. It is shown that (1) the neglected forces
(inertia associated with a nucleus rotation, solar tidal force) are,
in general, not negligible everywhere, and (2) when allowing for these
additional forces, a time-dependent model will, in general, have to
be used. The future steps of development of the model are outlined.
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Title: Comparison between Navier-Stokes and DSMC Simulations of the
Rarefied Gas Flow from Model Cometary Nuclei
Authors: Lukyanov, G. A.; Zakharov, V. V.; Rodionov, A. V.; Crifo,
J. F.
2005AIPC..762..331L Altcode:
We compare two fundamental ways of modeling the steady gas flows in
the near-nuclear atmosphere (coma) of comets. Several heliocentric
distances and several homogeneous non-rotating model nuclei - spherical
and aspherical - were considered, in order to cover a wide range of
boundary conditions at the surface of the nucleus and of gas flow
rarefaction in the coma. Two methods were used for simulations: (1)
the Direct Monte-Carlo Simulation (DSMC), (2) the so-called “BE-NSE”
method, which self-consistently solves the Boltzmann equation (BE)
in the immediate nonequilibrium vicinity of the nucleus surface,
and the Navier-Stokes equations (NSE) in the downstream region. For
the BE solution, a locally plane-parallel approximation is made,
using Cercignani's (1981) algorithms. The two methods were found to
agree over an unexpectedly large parameter range. To maximize the
modeling efficiency, a hybrid approach combining the BE-NSE approach
in the denser regions, with DSMC in the more rarefied regions is
also described.
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Title: Physical Model of the coma of Comet 67P/Churyumov-Gerasimenko
Authors: Crifo, J. F.; Lukyanov, G. A.; Zakharov, V. V.; Rodionov,
A. V.
2004ASSL..311..119C Altcode: 2004nrt..conf..119C
No abstract at ADS
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Title: Physical Model of the Coma of Comet 67P/Churyumov-Gerasimenko
Authors: Crifo, J. -F.; Rodionov, A. V.; Bockelée-Morvan, D.;
Lukyanov, G. A.; Zakharov, V. V.
2004cosp...35.1046C Altcode: 2004cosp.meet.1046C
Several Rosetta mission instruments will perform totally new
observations which require an extremely realistic physical modelling
of the coma -- not just approximate orders of magnitude: for instance,
the high resolution mm wave sounder MIRO, and the in-situ dust velocity
analyzer GIADA. In addition, the deposition of the lander will require
an accurate and predictive model of the gas distribution. We describe
the design specifications and the present state of an ongoing program
of three-dimensional, time-dependent, physically realistic simulation
of the gas and dust coma of the comet. The model excludes unphysical
simplifications: the nucleus can have any external shape, and assume any
realistic rotation state. The gas is assumed to be produced either by
surface sublimation, or by diffusion from the interior, or by both
processes, and the dust is assumed to be detached from it by the
aerodynamic force. Realistic dust shapes can be handled. To compute
the gas and dust distribution, the model uses Fluid Equations and/or
Direct Monte-Carlo Simulations. For want of space, we cannot show here
time-dependent simulations (see paper by A.V. Rodionov et al. in session
B1.2), but only present a few recent steady-state results illustrating
the present capabilities of the model: (1) an example of DSMC simulation
of the gas coma near 3 AU, revealing the extent of the fluid region;
(2) the computed structure of the near-nucleus gas and dust coma if the
nucleus has a shape similar to that considered possible by Lamy et al
(2003); (3) an example of DSMC simulation of the dynamics of heavy
grains (near to the lift-off limit), showing complex trajectories as
well as fall-backs onto the surface.
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Title: Navier-Stokes and direct Monte Carlo simulations of the
circumnuclear coma II. Homogeneous, aspherical sources
Authors: Crifo, J. F.; Loukianov, G. A.; Rodionov, A. V.; Zakharov,
V. V.
2003Icar..163..479C Altcode:
The dayside near-nucleus comae formed by solar-driven sublimation
from two different aspherical nuclei made of an homogeneous mixture
of ice and dust are computed by (1) solving Navier-Stokes equations
and (2) direct Monte Carlo simulations, for different nucleus sizes,
heliocentric distances, and dust-to-ice mixing ratios. Excellent
agreement between the two methods is found down to surprisingly
low production rates; it is found that the limit of validity of
the first method is not simply related to the coma rarefaction: a
new dimensionless number is tentatively offered to characterize this
limit. The present solutions show that the weak shocks always present
in the fluid coma persist practically down to truly free-molecular
conditions, excluding the observational discovery of a structureless
coma. They also show that rarefied flow in the near-nucleus coma can
have a quite complicated structure, in particular inside topographic
depressions. As an example, coma recondensation on the sunlit
flanks of a cavity was found to be possible. We compute, for the
first time, a true collisionless coma and show that structures are
still present in it but are confined to the immediate vicinity of the
surface. Finally, we describe in detail the kinetic conditions in a
rarefied water coma, i.e., the velocity distribution asymmetry and
the rotational-translational nonequilibrium. The significance of the
results for future missions to comets is outlined.
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Title: Comparison between Navier-Stokes and Direct Monte-Carlo
Simulations of the Circumnuclear Coma. I. Homogeneous, Spherical
Source
Authors: Crifo, J. F.; Lukianov, G. A.; Rodionov, A. V.; Khanlarov,
G. O.; Zakharov, V. V.
2002Icar..156..249C Altcode:
The structure of the near-nucleus H <SUB>2</SUB>O atmosphere formed by
sublimation under solar heating of a hypothetical large dusty ice sphere
is computed (1) by the direct simulation Monte-Carlo method (DSMC) and
(2) by solving Navier-Stokes equations (NSE) combined with a locally
plane-parallel solution of the collisional Boltzmann equation for the
nonequilibrium near-surface Knudsen layer. For Hale-Bopp-like comets,
perfect agreement is obtained between the two methods on the day and
night sides. This excellent agreement is maintained on the near-nucleus
dayside for less productive comets, even down to production rates as
low as those expected for Comet P/Wirtanen near 3 AU. It provides a
direct validation of the gasdynamic simulations performed in support
of the ESA Rosetta mission lander descent optimization studies (Crifo
et al. 2001) and also confirms the similarity between the dayside coma
and underexpanded axially symmetric free jets pointed out in Crifo
(1986). On the nightside, moderate to high discrepancies appear between
the two solutions as the production rate decreases, revealing the limits
of the NSE method. The limits of the present study are delineated,
and directions for future investigations are indicated.