scholarly journals VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: spectral properties and color temperature variability with phase and elevation

2019 ◽  
Vol 630 ◽  
pp. A22 ◽  
Author(s):  
D. Bockelée-Morvan ◽  
C. Leyrat ◽  
S. Erard ◽  
F. Andrieu ◽  
F. Capaccioni ◽  
...  
Keyword(s):  
Phase Angle ◽  
Thermal Inertia ◽  
Color Temperature ◽  
Dust Particles ◽  
Infrared Thermal Imaging ◽  
Imaging Spectrometer ◽  
Fixed Phase ◽  
Dust Coma ◽  
Solar Phase ◽  
Comet 67P

We analyze 2–5 μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distances rh = 1.24–1.55 AU. The 2–2.5 μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained at α = 90° solar phase angle show an increase in bolometric albedo (0.05–0.14) with increasing altitude (0.5–8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°–120°, phase reddening is significant (0.031%/100 nm deg−1) for a mean color of 2%/100 nm at α = 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg−1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α = 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow a rh−0.6 variation in the rh = 1.24–1.5 AU range, which is close to the expected rh−0.5 value.

scholarly journals Analysis of night-side dust activity on comet 67P observed by VIRTIS-M: a new method to constrain the thermal inertia on the surface

2019 ◽  
Vol 630 ◽  
pp. A21 ◽  
Author(s):  
G. Rinaldi ◽  
M. Formisano ◽  
D. Kappel ◽  
F. Capaccioni ◽  
D. Bockelée-Morvan ◽  
...  
Keyword(s):  
Thermal Inertia ◽  
Numerical Code ◽  
Infrared Thermal Imaging ◽  
Imaging Spectrometer ◽  
Water Ice ◽  
Night Side ◽  
Color Gradient ◽  
3D Finite Element Method ◽  
Comet 67P ◽  
Subsurface Temperatures

On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25–36 W K−1 m−2 s−1/2. These thermal inertia values can be used to verify with a 3D finite-element method (FEM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m−2 K−1 s−0.5; (2) the same structure, but with thermal inertia of 100 J m−2 K−1 s−0.5; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 ± 4.8%/100 nm to 13 ± 2.6%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between −2.5 and −3.

scholarly journals Interpretation through experimental simulations of phase functions revealed by Rosetta in 67P/Churyumov-Gerasimenko dust coma

2019 ◽  
Vol 630 ◽  
pp. A20 ◽  
Author(s):  
A. C. Levasseur-Regourd ◽  
J.-B. Renard ◽  
E. Hadamcik ◽  
J. Lasue ◽  
I. Bertini ◽  
...  
Keyword(s):  
Heliocentric Distance ◽  
Size Range ◽  
Interplanetary Dust ◽  
Dust Particles ◽  
Zodiacal Cloud ◽  
Cometary Dust ◽  
Microgravity Conditions ◽  
Dust Coma ◽  
Phase Functions ◽  
Comet 67P

Context. The dust-brightness phase curves that have been measured by the OSIRIS cameras on board the Rosetta spacecraft within the coma of comet 67P/Churyumov-Gerasimenko (67P) present a remarkable flattened u-shape. Aims. Our goal is to compare these phase curves with those of tentatively analog dust samples to assess the key dust properties that might induce this shape. Methods. Light-scattering measurements have been made with the PROGRA2 instrument in the laboratory and in microgravity conditions on samples of different physical properties and compositions that are likely to be representative of cometary dust particles. Results. We find that the brightness phase curves of a series of interplanetary dust analogs that have been recently developed (to fit the polarimetric properties of the inner zodiacal cloud and their changes with heliocentric distance) are quite comparable to those of 67P. Key dust properties seem to be related to the composition and the porosity. Conclusions. We conclude that the shape of the brightness phase curves of 67P has to be related to the presence of a significant amount of organic compounds (at least 50% in mass) and of fluffy aggregates (of a size range of 10–200 μm). We also confirm similarities between the dust particles of this Jupiter-family comet and the particles within the inner zodiacal cloud.

scholarly journals High polarization degree of the continuum of comet 2P/Encke based on spectropolarimetric signals during its 2017 apparition

2018 ◽  
Vol 620 ◽  
pp. A161
Author(s):  
Y. G. Kwon ◽  
M. Ishiguro ◽  
Y. Shinnaka ◽  
T. Nakaoka ◽  
D. Kuroda ◽  
...  
Keyword(s):  
Phase Angle ◽  
Near Infrared ◽  
Scattered Light ◽  
Infrared Camera ◽  
Polarization Vector ◽  
Dust Particles ◽  
Polarization Degree ◽  
High Polarization ◽  
Solar Phase ◽  
The Continuum

Context. Spectropolarimetry is a powerful technique for investigating the physical properties of gas and solid materials in cometary comae without mutual contamination, but only a few spectropolarimetric studies have been conducted to extract each component. Aims. We attempt to derive the continuum (i.e., scattered light from dust coma) polarization degree of comet 2P/Encke, free of the influence of molecular emissions. The target is unique in that its orbit is dynamically decoupled from Jupiter, like the main-belt asteroids, but it ejects gas and dust like ordinary comets. Methods. We observed the comet using the Hiroshima Optical and Near-Infrared Camera attached to the Cassegrain focus of the 150 cm Kanata telescope on UT 2017 February 21 when the comet was at the solar phase angle of α = 75°.7. Results. We find that the continuum polarization degree with respect to the scattering plane is Pcont, r = 33.8 ± 2.7% at the effective wavelength of 0.82 μm, which is significantly higher than those of cometary dust in a high-Pmax group at similar phase angles. Assuming that an ensemble polarimetric response of the dust of 2P/Encke as a function of phase angle is morphologically similar with those of other comets, its maximum polarization degree is estimated to Pmax ≳ 40% at αmax ≈ 100°. In addition, we obtain the polarization degrees of the C2 swan bands (0.51–0.56 μm), the NH2 α bands (0.62–0.69 μm), and the CN-red system (0.78–0.94 μm) in a range of 3–19%, which depend on the molecular species and rotational quantum numbers of each branch. The polarization vector is aligned nearly perpendicularly to the scattering plane with an average of 0°.4 over a wavelength range of 0.50–0.97 μm. Conclusions. From the observational evidence, we conjecture that the high polarization degree of 2P/Encke might be attributable to a dominance of large dust particles around the nucleus, which have remained after frequent perihelion passages near the Sun.

scholarly journals Modelling observations of the inner gas and dust coma of comet 67P/Churyumov-Gerasimenko using ROSINA/COPS and OSIRIS data: First results

2016 ◽  
Vol 589 ◽  
pp. A90 ◽  
Author(s):  
R. Marschall ◽  
C. C. Su ◽  
Y. Liao ◽  
N. Thomas ◽  
K. Altwegg ◽  
...  
Keyword(s):  
First Results ◽  
Dust Coma ◽  
Comet 67P

scholarly journals CO-driven activity constrains the origin of comets

2020 ◽  
Vol 636 ◽  
pp. L3 ◽  
Author(s):  
M. Fulle ◽  
J. Blum ◽  
A. Rotundi
Keyword(s):  
Loss Rate ◽  
Dust Particles ◽  
Mass Ratio ◽  
Cometary Nuclei ◽  
Nucleus Surface ◽  
Activity Onset ◽  
Gas Loss ◽  
Open Question ◽  
Comet 67P ◽  
Co Gas

Context. An open question in the study of comets is the so-called cohesion bottleneck, that is, how dust particles detach from the nucleus. Aims. We test whether the CO pressure buildup inside the pebbles of which cometary nuclei consist can overcome this cohesion bottleneck. Methods. A recently developed pebble-diffusion model was applied here to comet C/2017K2 PANSTARRS, assuming a CO-driven activity. Results. (i) The CO-gas pressure inside the pebbles erodes the nucleus into the observed dust, which is composed of refractories, H2O ice and CO2 ice. (ii) The CO-driven activity onset occurs up to heliocentric distances of 85 au, depending on the spin orientation of the comet nucleus. (iii) The activity onset observed at ≈26 au suggests a low obliquity of the nucleus spin axis with activity in a polar summer. (iv) At 14 au, the smallest size of the ejected dust is ≈0.1 mm, consistent with observations. (v) The observed dust-loss rate of ≈200 kg s−1 implies a fallout ≥30%, a nucleus surface active area ≥10 km2, a CO-gas loss rate ≥10 kg s−1, and a dust-to-gas ratio ≤20. (vi) The CO-driven activity never stops if the average refractory-to-all-ices mass ratio in the nucleus is ≤4.5 for a nucleus all-ices-to-CO mass ratio ≈4, as observed in comets Hale–Bopp and Hyakutake. These results make comet C/2017K2 similar to the Rosetta target comet 67P/Churyumov–Gerasimenko. (vii) The erosion lifetime of cometary planetesimals is a factor 103 shorter than the timescale of catastrophic collisions. This means that the comets we observe today cannot be products of catastrophic collisions.

Dayside-to-nightside dust coma brightness asymmetry and its implications for nightside activity at Comet 67P/Churyumov–Gerasimenko

Icarus ◽  
2020 ◽  
Vol 351 ◽  
pp. 113968 ◽  
Author(s):  
S.-B. Gerig ◽  
O. Pinzón-Rodríguez ◽  
R. Marschall ◽  
J.-S. Wu ◽  
N. Thomas
Keyword(s):  
Dust Coma ◽  
Comet 67P

scholarly journals Dust of comet 67P/Churyumov-Gerasimenko collected by Rosetta/MIDAS: classification and extension to the nanometer scale

2019 ◽  
Vol 630 ◽  
pp. A26 ◽  
Author(s):  
T. Mannel ◽  
M. S. Bentley ◽  
P. D. Boakes ◽  
H. Jeszenszky ◽  
P. Ehrenfreund ◽  
...  
Keyword(s):  
Interplanetary Dust ◽  
Dust Particles ◽  
Nanometer Scale ◽  
Early Solar System ◽  
Interplanetary Dust Particles ◽  
Surface Features ◽  
Cometary Dust ◽  
Log Normal ◽  
Resolution Of Imaging ◽  
Comet 67P

Context. The properties of the smallest subunits of cometary dust contain information on their origin and clues to the formation of planetesimals and planets. Compared to interplanetary dust particles or particles collected during the Stardust mission, dust collected in the coma of comet 67P/Churyumov-Gerasimenko (67P) during the Rosetta mission provides a resource of minimally altered material with known origin whose structural properties can be used to further the investigation of the early solar system. Aims. The cometary dust particle morphologies found at comet 67P on the micrometer scale are classified, and their structural analysis is extended to the nanometer scale. Methods. We present a novel method for achieving the highest spatial resolution of imaging obtained with the MIDAS Atomic Force Microscope on board Rosetta. 3D topographic images with resolutions down to 8 nm were analyzed to determine the subunit sizes of particles on the nanometer scale. Results. Three morphological classes can be determined: (i) fragile agglomerate particles of sizes larger than about 10 μm comprised of micrometer-sized subunits that may themselves be aggregates and show a moderate packing density on the surface of the particles. (ii) A fragile agglomerate with a size of about a few tens of micrometers comprised of micrometer-sized subunits that are suggested to be aggregates themselves and are arranged in a structure with a fractal dimension lower than two. (iii) Small micrometer-sized particles comprised of subunits in the size range of hundreds of nanometers that show surface features that are again suggested to represent subunits. Their differential size distributions follow a log-normal distribution with means of about 100 nm and standard deviations between 20 and 35 nm. Conclusions. The properties of the dust particles found by MIDAS represent an extension of the dust results of Rosetta to the micro- and nanometer scale. All micrometer-sized particles are hierarchical dust agglomerates of smaller subunits. The arrangement, appearance, and size distribution of the smallest determined surface features are reminiscent of those found in chondritic porous interplanetary dust particles. They represent the smallest directly detected subunits of comet 67P.

scholarly journals Study of a Far Infrared Cavity Around a Post-Asymptotic Giant Branch Star at Galactic Latitude -0.1º

2020 ◽  
Vol 6 (1) ◽  
pp. 97-104
Author(s):  
A. K. Gautam
Keyword(s):  
Galactic Plane ◽  
Far Infrared ◽  
Asymptotic Giant Branch ◽  
Color Temperature ◽  
Dust Particles ◽  
Galactic Latitude ◽  
Continuous Increase ◽  
Asymptotic Giant Branch Star ◽  
Planck Function ◽  
Visual Extinction

We present dust color temperature, Planck function and visual extinction distributions of a far infrared cavity FIC19+30 found to be located around post-AGB star namely AGB20+29 at the galactic plane. Minimum and maximum dust color temperature of the core region of the cavity was found to be (22.17±0.23) K and (22.41±0.29) K respectively with offset value 0.24 K which suggests that the cavity is isolated and stable. The product of dust color temperature and visual extinction was found to be in the order of 10-4 K mag. The distribution of Planck function along the extension (major diameter) and compression (minor diameter) was found to be non-uniform distribution. Specifically dust particles are oscillating in order to get dynamical equilibrium which may be the cause of grain temperature. It further suggests that the dust particles in the cavities might not be in the thermal equilibrium possibly due to pressure driven events of nearby AGB stars. There is continuous increase in flux density with increase in wavelength as in case of nebula which suggests that number density of dust particles increase according to the increase in wavelength and vice-versa.

scholarly journals Study of Dust Properties of two Far Infrared Cavities near by Asymptotic Giant Branch stars under Infrared Astronomical Satellite Maps

2020 ◽  
pp. 60-71
Author(s):  
M. Tiwari ◽  
S.P. Gautam ◽  
A. Silwal ◽  
S. Subedi ◽  
A. Paudel ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Far Infrared ◽  
Asymptotic Giant Branch ◽  
Color Temperature ◽  
Dust Particles ◽  
Planck Function ◽  
Visual Extinction ◽  
Contour Plots ◽  
Infrared Astronomical Satellite ◽  
Astronomical Satellite

The physical properties such as dust color temperature, dust mass, visual extinction, and Planck function with their distribution in the core region of two far-infrared cavities, namely FIC16-37 (size ~ 4.79 pc x 3.06 pc) located at R.A. (J2000): 16h 33m 57.25s & Dec. (J2000): -37d 47m 04.3s, and FIC12-58 (size ~ 22.54 pc x 14.84 pc) located at R.A. (J2000): 12h 52m 50.08s & Dec. (J2000): -58d 08m 55.02s, found within a galactic plane -10o  to +10o  nearby Asymptotic Giant Branch (AGB) stars namely AGB15-38 (R.A. (J2000): 15h 37m 40.74s & Dec. (J2000): -38d 20m 24.6s), and AGB12-57 (R.A (J2000): 12h 56m 38.50s & Dec. (J2000): -57d 54m 34.70s), respectively were studied using Infrared Astronomical Satellite (IRAS) survey. The dust color temperature was found to lie in the range of 23.95 ± 0.25 K to 23.44 ± 0.27 K with an offset about 0.5 K for FIC16-37, and 24.88 ± 0.27 K to 23.63 ± 0.98 K with an offset about 1 K for FIC12-58. The low offset in the dust color temperature indicated the symmetric distribution of density and temperature. The total mass of the cavities FIC16-37 and FIC12-58 were found to be 0.053 M☉ and 0.78 M☉, respectively. The contour plots of mass distribution of both of the cavities was found to follow the cosmological principle, suggesting the homogeneous and isotropic distribution of dust masses. The plot between temperature and visual extinction showed a negative correlation, suggesting that higher temperature has lower visual extinction and vice-versa. The distribution of Planck function along major and minor diameters of both of the cavities was found to be non-uniform, indicating oscillation of dust particles to get dynamical equilibrium. It further suggested the role of pressure-driven events nearby both cavities and suggested that dust particles are not in thermal equilibrium along the diameters.

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