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1. Modeling of the outburst on July 29th, 2015 observed with OSIRIS cameras in the southern hemisphere of comet 67P/Churyumov-Gerasimenko

Author

Gicquel, A., Rose, M., Vincent, J. -B., Davidsson, B., Bodewits, D., Hearn, M. F. A, Agarwal, J., Fougere, N., Sierks, H., Bertini, I., Lin, Z. -Y., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Barucci, M. A., Bertaux, J. -L., Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guttler, C., Hofner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuhrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

Images of the nucleus and the coma (gas and dust) of comet 67P/Churyumov- Gerasimenko have been acquired by the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras since March 2014 using both the Wide Angle Camera (WAC) and the Narrow Angle Camera (NAC). We use images from the NAC camera to study a bright outburst observed in the southern hemisphere on July 29, 2015. The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus. The heliocentric distance is 1.25 au and the spacecraft-comet distance is 186 km. Aiming to better understand the physics that led to the outgassing, we used the Direct Simulation Monte Carlo (DSMC) method to study the gas flow close to the nucleus and the dust trajectories. The goal is to understand the mechanisms producing the outburst. We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region. The outburst is in fact a combination of both gas and dust, in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas. We need a number of dust particles 7.83 $\times$ 10$^{11}$ - 6.90 $\times$ 10$^{15}$ (radius 1.97 - 185 {\mu}m), which corresponds to a mass of dust 220 - 21 $\times$ 10$^{3}$kg., Comment: 8 pages, 9 figures

Published
2017
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2. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Author

Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Sierks, H., Agarwal, J., A'Hearn, M., Bertaux, J. -L., Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Güttler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kührt, E., Küppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Oklay, N., Shi, X., Tubiana, C., and Vincent, J. -B.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the OSIRIS instrument during the closest fly-by over the comet, which took place on 14 th February 2015 at a distance of {\~} 6 km from the surface. Several images covering the 0{\deg}-33{\deg} phase angle range were acquired, and the spatial resolution achieved was 11 cm/pxl. The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40{\%} between bright spots and sombre regions, and spectral slope variations up to 50{\%}. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our dataset using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8{\%}) and it has a high porosity value in the uppermost-layers (86{\%}). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus., Comment: 19 pages, 16 figures, 5 tables, (also presented at DPS48/ESPC11: http://cdsads.u-strasbg.fr/abs/2016DPS....4830004F)

Published
2016
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3. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras onboard Rosetta

Author

Gicquel, A., Vincent, J. -B., Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Lin, Z. -Y., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Barucci, M. A., Bertaux, J. -L., Besse, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

Beginning in March 2014, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analyzed the dust monitoring observations shortly after the southern vernal equinox on May 30 and 31, 2015 with the WAC at the heliocentric distance Rh = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this article was that through the sublimation of the aggregates of dirty grains (radius a between 5 microm and 50 microm) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data we needed to inject a number of aggregates between 8.5 x $10^{13}$ and 8.5 x $10^{10}$ for a = 5 microm and 50 microm respectively, or an initial mass of $H_2O$ ice around 22kg., Comment: 11 pages, 7 figures, 3 tables, special issue "The ESLAB 50 Symposium - spacecraft at comets from 1P/Halley to 67P/Churyumov-Gerasimenko" in the Monthly Notices of the Royal Astronomical Society

Published
2016
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8. Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

Author

Masoumzadeh, N., Kolokolova, L., Tubiana, C., El-Maarry, M. R., Mottola, S., Güttler, C., Snodgrass, C, Sierks, H., Naletto, G., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Davidsson, B., Barucci, M.A., Bertaux, J.L., Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, Vania, Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gutiérrez, Pedro J., Hasselmann, P.H., Ip, W. H., Keller, H.U., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Shi, X., Toth, I., Masoumzadeh, N., Kolokolova, L., Tubiana, C., El-Maarry, M. R., Mottola, S., Güttler, C., Snodgrass, C, Sierks, H., Naletto, G., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Davidsson, B., Barucci, M.A., Bertaux, J.L., Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, Vania, Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gutiérrez, Pedro J., Hasselmann, P.H., Ip, W. H., Keller, H.U., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Shi, X., and Toth, I.

Abstract

The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9-10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences.© N. Masoumzadeh et al. 2019

Published
2019

9. Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

Author

Masoumzadeh, N, primary, Kolokolova, L, additional, Tubiana, C, additional, El-Maarry, M. R., additional, Mottola, S, additional, Güttler, C., additional, Snodgrass, C, additional, Sierks, H., additional, Naletto, G., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D, additional, Davidsson, B, additional, Barucci, M. A., additional, Bertaux, J.-L., additional, Bertini, I, additional, Bodewits, D., additional, Cremonese, G, additional, Da Deppo, V., additional, Debei, S., additional, De Cecco, M., additional, Deller, J., additional, Fornasier, S., additional, Fulle, M, additional, Gutiérrez, P. J., additional, Hasselmann, P. H., additional, Ip, W.-H., additional, Keller, H. U., additional, Lara, L. M., additional, Lazzarin, M, additional, López-Moreno, J. J., additional, Marzari, F, additional, Shi, X, additional, and Toth, I, additional

Published
2019
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10. Exposed bright features on the comet 67P/Churyumov-Gerasimenko : distribution and evolution

Author

Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Hasselmann, P. H., Feller, C., Sierks, H., Lucchetti, A., Pajola, M., Oklay, N., Mottola, S., Masoumzadeh, N., Tubiana, C., Guettler, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Groussin, O., Gutierrez, P. J., Hoang, H. V., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kuppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Preusker, F., Shi, X., Thomas, N., Vincent, J. -B, Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Hasselmann, P. H., Feller, C., Sierks, H., Lucchetti, A., Pajola, M., Oklay, N., Mottola, S., Masoumzadeh, N., Tubiana, C., Guettler, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Groussin, O., Gutierrez, P. J., Hoang, H. V., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kuppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Preusker, F., Shi, X., Thomas, N., and Vincent, J. -B

Abstract

Context. Since its arrival at the comet 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta. Aims. We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance. Methods. We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel-Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest. Results. We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of H2O ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category. Conclusions. Although the nucleus of 67P/Churyumov-Gerasimenko appears to be dark in general, there are localised H2O ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated H2O ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet's return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated H2O ice that is prese

Published
2018
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11. Exposed bright features on the comet 67P/Churyumov-Gerasimenko: Distribution and evolution

Author

German Centre for Air and Space Travel, Centre National D'Etudes Spatiales (France), Agenzia Spaziale Italiana, Ministerio de Educación y Ciencia (España), European Space Agency, Swedish National Space Board, Deshapriya, J.D.P., Barucci, M.A., Fornasier, S., Hasselmann, P.H., Feller, C., Sierks, H., Lucchetti, A., Pajola, M., Oklay, N., Mottola, S., Masoumzadeh, N., Tubiana, C., Güttler, C., Barbieri, C., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Rickman, H., Bertaux, J.L., Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, Vania, Davidsson, Björn J. R., Debei, S., Cecco, M.D., Deller, J., Fulle, M., Groussin, O., Gutiérrez, Pedro J., Hoang, H. V., Hviid, S.F., Ip, W. H., Jorda, L., Keller, H.U., Knollenberg, J., Kramm, R., Kührt, E., Küppers, M., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Naletto, G., Preusker, F., Shi, X., Thomas, N., Vincent, J.B., German Centre for Air and Space Travel, Centre National D'Etudes Spatiales (France), Agenzia Spaziale Italiana, Ministerio de Educación y Ciencia (España), European Space Agency, Swedish National Space Board, Deshapriya, J.D.P., Barucci, M.A., Fornasier, S., Hasselmann, P.H., Feller, C., Sierks, H., Lucchetti, A., Pajola, M., Oklay, N., Mottola, S., Masoumzadeh, N., Tubiana, C., Güttler, C., Barbieri, C., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Rickman, H., Bertaux, J.L., Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, Vania, Davidsson, Björn J. R., Debei, S., Cecco, M.D., Deller, J., Fulle, M., Groussin, O., Gutiérrez, Pedro J., Hoang, H. V., Hviid, S.F., Ip, W. H., Jorda, L., Keller, H.U., Knollenberg, J., Kramm, R., Kührt, E., Küppers, M., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Naletto, G., Preusker, F., Shi, X., Thomas, N., and Vincent, J.B.

Abstract

Context. Since its arrival at the comet 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta. Aims. We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance. Methods. We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel-Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest. Results. We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of HO ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category. Conclusions. Although the nucleus of 67P/Churyumov-Gerasimenko appears to be dark in general, there are localised HO ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated HO ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet's return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated HO ice that is preserved

Published
2018

12. The backscattering ratio of comet 67P/Churyumov-Gerasimenko dust coma as seen by OSIRIS onboard Rosetta

Author

Bertini, I, primary, Forgia, F La, additional, Fulle, M, additional, Tubiana, C, additional, Güttler, C, additional, Moreno, F, additional, Agarwal, J, additional, Munoz, O, additional, Mottola, S, additional, Ivanovsky, S, additional, Pajola, M, additional, Lucchetti, A, additional, Petropoulou, V, additional, Lazzarin, M, additional, Rotundi, A, additional, Bodewits, D, additional, Frattin, E, additional, Toth, I, additional, Masoumzadeh, N, additional, Kovacs, G, additional, Rinaldi, G, additional, Guirado, D, additional, Sierks, H, additional, Naletto, G, additional, Lamy, P, additional, Rodrigo, R, additional, Koschny, D, additional, Davidsson, B, additional, Barbieri, C, additional, Barucci, M A, additional, Bertaux, J-L, additional, Cambianica, P, additional, Cremonese, G, additional, Da Deppo, V, additional, Debei, S, additional, De Cecco, M, additional, Deller, J, additional, Ferrari, S, additional, Ferri, F, additional, Fornasier, S, additional, Gutierrez, P J, additional, Hasselmann, P H, additional, Ip, W-H, additional, Keller, H U, additional, Lara, L M, additional, Moreno, J J Lopez, additional, Marzari, F, additional, Massironi, M, additional, Penasa, L, additional, and Shi, X, additional

Published
2018
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13. Exposed bright features on the comet 67P/Churyumov–Gerasimenko: distribution and evolution

Author

Deshapriya, J. D. P., primary, Barucci, M. A., additional, Fornasier, S., additional, Hasselmann, P. H., additional, Feller, C., additional, Sierks, H., additional, Lucchetti, A., additional, Pajola, M., additional, Oklay, N., additional, Mottola, S., additional, Masoumzadeh, N., additional, Tubiana, C., additional, Güttler, C., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, Bertaux, J.-L., additional, Bertini, I., additional, Bodewits, D., additional, Boudreault, S., additional, Cremonese, G., additional, Da Deppo, V., additional, Davidsson, B. J. R., additional, Debei, S., additional, De Cecco, M., additional, Deller, J., additional, Fulle, M., additional, Groussin, O., additional, Gutierrez, P. J., additional, Hoang, H. V., additional, Hviid, S. F., additional, Ip, W., additional, Jorda, L., additional, Keller, H. U., additional, Knollenberg, J., additional, Kramm, R., additional, Kührt, E., additional, Küppers, M., additional, Lara, L., additional, Lazzarin, M., additional, Lopez Moreno, J. J., additional, Marzari, F., additional, Naletto, G., additional, Preusker, F., additional, Shi, X., additional, Thomas, N., additional, and Vincent, J.-B., additional

Published
2018
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14. Long-term survival of surface water ice on comet 67P

Author

Oklay, N., Mottola, S., Vincent, J. -B, Pajola, M., Fornasier, S., Hviid, S. F., Kappel, D., Kuehrt, E., Keller, H. U., Barucci, M. A., Feller, C., Preusker, F., Scholten, F., Hall, I., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hasselmann, P. H., Hofmann, M., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Masoumzadeh, N., Naletto, G., Pommerol, A., Shi, X., Thomas, N., Tubiana, C., Oklay, N., Mottola, S., Vincent, J. -B, Pajola, M., Fornasier, S., Hviid, S. F., Kappel, D., Kuehrt, E., Keller, H. U., Barucci, M. A., Feller, C., Preusker, F., Scholten, F., Hall, I., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hasselmann, P. H., Hofmann, M., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Masoumzadeh, N., Naletto, G., Pommerol, A., Shi, X., Thomas, N., and Tubiana, C.

Abstract

Numerous water-ice-rich deposits surviving more than several months on comet 67P/Churyumov-Gerasimenko were observed during the Rosetta mission. We announce the first-time detection of water-ice features surviving up to 2 yr since their first observation via OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) NAC (narrow angle camera). Their existence on the nucleus of comet 67P at the arrival of the Rosetta spacecraft suggests that they were exposed to the surface during the comet's previous orbit. We investigated the temporal variation of large water-ice patches to understand the long-term sustainability of water ice on cometary nuclei on time-scales of months and years. Large clusters are stable over typical periods of 0.5 yr and reduce their size significantly around the comet's perihelion passage, while small exposures disappear. We characterized the temporal variation of their multispectral signatures. In large clusters, dust jets were detected, whereas in large isolated ones no associated activity was detected. Our thermal analysis shows that the long-term sustainability of water-ice-rich features can be explained by the scarce energy input available at their locations over the first half year. However, the situation reverses for the period lasting several months around perihelion passage. Our two end-member mixing analysis estimates a pure water-ice equivalent thickness up to 15 cm within one isolated patch, and up to 2 m for the one still observable through the end of the mission. Our spectral modelling estimates up to 48 per cent water-ice content for one of the large isolated feature, and up to 25 per cent water ice on the large boulders located within clusters.

Published
2017
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15. Modelling of the outburst on 2015 July 29 observed with OSIRIS cameras in the Southern hemisphere of comet 67P/Churyumov-Gerasimenko

Author

Gicquel, A., Rose, M., Vincent, J. -B, Davidsson, B., Bodewits, D., A'Hearn, M. F., Agarwal, J., Fougere, N., Sierks, H., Bertini, I., Lin, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Rose, M., Vincent, J. -B, Davidsson, B., Bodewits, D., A'Hearn, M. F., Agarwal, J., Fougere, N., Sierks, H., Bertini, I., Lin, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Abstract

Images of the nucleus and the coma (gas and dust) of comet 67P/Churyumov-Gerasimenko have been acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) cameras since 2014 March using both the wide-angle camera and the narrow-angle camera (NAC). We use images from the NAC camera to study a bright outburst observed in the Southern hemisphere on 2015 July 29. The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus. The heliocentric distance is 1.25 au and the spacecraft-comet distance is 186 km. Aiming to better understand the physics that led to the outgassing, we used the Direct Simulation Monte Carlo method to study the gas flow close to the nucleus and the dust trajectories. The goal is to understand the mechanisms producing the outburst. We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region. The outburst is in fact a combination of both gas and dust, in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas. We need a number of dust particles 7.83 x 10(11) to 6.90 x 10(15) (radius 1.97-185 mu m), which correspond to a mass of dust (220-21) x 10(3) kg.

Published
2017
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16. Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Author

Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M. A., Vincent, J. -B, Tubiana, C., Guettler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P. H., Feller, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M. A., Vincent, J. -B, Tubiana, C., Guettler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P. H., Feller, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., and Thomas, N.

Abstract

Aims. We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.

Published
2017
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17. Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Author

Swedish National Space Board, Ministerio de Economía y Competitividad (España), Agenzia Spaziale Italiana, Centre National de la Recherche Scientifique (France), German Centre for Air and Space Travel, European Space Agency, Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M.A., Vincent, J.B., Tubiana, C., Güttler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P.H., Feller, C., Barbieri, C., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Rickman, H., A'Hearn, M. F., Bertaux, J.L., Bertini, I., Cremonese, G., Da Deppo, Vania, Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, Pedro J., Hall, I., Hofmann, M., Hviid, S.F., Ip, W. H., Jorda, L., Keller, H.U., Knollenberg, J., Kovacs, G., Kramm, J.R., Kührt, E., Küppers, M., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Naletto, G., Shi, X., Thomas, N., Swedish National Space Board, Ministerio de Economía y Competitividad (España), Agenzia Spaziale Italiana, Centre National de la Recherche Scientifique (France), German Centre for Air and Space Travel, European Space Agency, Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M.A., Vincent, J.B., Tubiana, C., Güttler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P.H., Feller, C., Barbieri, C., Lamy, P.L., Rodrigo Montero, Rafael, Koschny, D., Rickman, H., A'Hearn, M. F., Bertaux, J.L., Bertini, I., Cremonese, G., Da Deppo, Vania, Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, Pedro J., Hall, I., Hofmann, M., Hviid, S.F., Ip, W. H., Jorda, L., Keller, H.U., Knollenberg, J., Kovacs, G., Kramm, J.R., Kührt, E., Küppers, M., Lara, Luisa María, Lazzarin, M., López-Moreno, José Juan, Marzari, F., Naletto, G., Shi, X., and Thomas, N.

Abstract

Aims. We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.© ESO, 2017.

Published
2017

18. Long-term survival of surface water ice on comet 67P

Author

Oklay, N., primary, Mottola, S., additional, Vincent, J.-B., additional, Pajola, M., additional, Fornasier, S., additional, Hviid, S. F., additional, Kappel, D., additional, Kührt, E., additional, Keller, H. U., additional, Barucci, M. A., additional, Feller, C., additional, Preusker, F., additional, Scholten, F., additional, Hall, I., additional, Sierks, H., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, A’Hearn, M. F., additional, Bertaux, J.-L., additional, Bertini, I., additional, Bodewits, D., additional, Cremonese, G., additional, Da Deppo, V., additional, Davidsson, B. J. R., additional, Debei, S., additional, De Cecco, M., additional, Deller, J., additional, Deshapriya, J. D. P., additional, Fulle, M., additional, Gicquel, A., additional, Groussin, O., additional, Gutiérrez, P. J., additional, Güttler, C., additional, Hasselmann, P. H., additional, Hofmann, M., additional, Ip, W.-H., additional, Jorda, L., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Küppers, M., additional, Lara, L. M., additional, Lazzarin, M., additional, Lin, Z.-Y., additional, Moreno, J. J. Lopez, additional, Lucchetti, A., additional, Marzari, F., additional, Masoumzadeh, N., additional, Naletto, G., additional, Pommerol, A., additional, Shi, X., additional, Thomas, N., additional, and Tubiana, C., additional

Published
2017
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19. Modelling of the outburst on 2015 July 29 observed with OSIRIS cameras in the Southern hemisphere of comet 67P/Churyumov–Gerasimenko

Author

Gicquel, A., primary, Rose, M., additional, Vincent, J.-B., additional, Davidsson, B., additional, Bodewits, D., additional, A’Hearn, M. F., additional, Agarwal, J., additional, Fougere, N., additional, Sierks, H., additional, Bertini, I., additional, Lin, Z.-Y., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, Keller, H. U., additional, Barucci, M. A., additional, Bertaux, J.-L., additional, Besse, S., additional, Boudreault, S., additional, Cremonese, G., additional, Da Deppo, V., additional, Debei, S., additional, Deller, J., additional, De Cecco, M., additional, Frattin, E., additional, El-Maarry, M. R., additional, Fornasier, S., additional, Fulle, M., additional, Groussin, O., additional, Gutiérrez, P. J., additional, Gutiérrez-Marquez, P., additional, Güttler, C., additional, Höfner, S., additional, Hofmann, M., additional, Hu, X., additional, Hviid, S. F., additional, Ip, W.-H., additional, Jorda, L., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Kührt, E., additional, Küppers, M., additional, Lara, L. M., additional, Lazzarin, M., additional, Moreno, J. J. Lopez, additional, Lowry, S., additional, Marzari, F., additional, Masoumzadeh, N., additional, Massironi, M., additional, Moreno, F., additional, Mottola, S., additional, Naletto, G., additional, Oklay, N., additional, Pajola, M., additional, Preusker, F., additional, Scholten, F., additional, Shi, X., additional, Thomas, N., additional, Toth, I., additional, and Tubiana, C., additional

Published
2017
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20. Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Author

Masoumzadeh, N., primary, Oklay, N., additional, Kolokolova, L., additional, Sierks, H., additional, Fornasier, S., additional, Barucci, M. A., additional, Vincent, J.-B., additional, Tubiana, C., additional, Güttler, C., additional, Preusker, F., additional, Scholten, F., additional, Mottola, S., additional, Hasselmann, P. H., additional, Feller, C., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, A’Hearn, M. F., additional, Bertaux, J.-L., additional, Bertini, I., additional, Cremonese, G., additional, Da Deppo, V., additional, Davidsson, B. J. R., additional, Debei, S., additional, De Cecco, M., additional, Fulle, M., additional, Gicquel, A., additional, Groussin, O., additional, Gutiérrez, P. J., additional, Hall, I., additional, Hofmann, M., additional, Hviid, S. F., additional, Ip, W.-H., additional, Jorda, L., additional, Keller, H. U., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Kührt, E., additional, Küppers, M., additional, Lara, L. M., additional, Lazzarin, M., additional, Lopez Moreno, J. J., additional, Marzari, F., additional, Naletto, G., additional, Shi, X., additional, and Thomas, N., additional

Published
2017
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21. The backscattering ratio of comet 67P/Churyumov–Gerasimenko dust coma as seen by OSIRIS onboard Rosetta.

Author

Bertini, I, La Forgia, F, Fulle, M, Tubiana, C, Güttler, C, Moreno, F, Agarwal, J, Munoz, O, Mottola, S, Ivanovsky, S, Pajola, M, Lucchetti, A, Petropoulou, V, Lazzarin, M, Rotundi, A, Bodewits, D, Frattin, E, Toth, I, Masoumzadeh, N, and Kovacs, G

Subjects
BACKSCATTERING, COSMIC dust, REMOTE sensing, STELLAR evolution, ASTRONOMICAL observations
Abstract

Remote sensing observations of dust particles ejected from comets provide important hints on the intimate nature of the materials composing these primitive objects. The measurement of dust coma backscattering ratio, BSR, defined as the ratio of the reflectance at phase angle 0° and 30°, helps tuning theoretical models aimed at solving the inverse scattering problem deriving information on the nature of the ejected particles. The Rosetta /OSIRIS camera sampled the coma phase function of comet 67P, with four series acquired at low phase angles from 2015 January to 2016 May. We also added previously published data to our analysis to increase the temporal resolution of our findings. We measured a BSR in the range ∼ [1.7–3.6], broader than the range found in literature from ground-based observations of other comets. We found that during the post-perihelion phase, the BSR is systematically larger than the classical cometary dust values only for nucleocentric distances smaller than ∼100 km. We explain this trend in terms of a cloud of chunks orbiting the nucleus at distances <100 km ejected during perihelion and slowly collapsing on the nucleus over a few months because of the coma gas drag. This also implies that the threshold particle size for the dust phase function to become similar to the nucleus phase function is between 2.5 mm and 0.1 m, taking into account previous Rosetta findings. [ABSTRACT FROM AUTHOR]

Published
2019
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22. Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Author

Oklay, N., Vincent, J. -B, Fornasier, S., Pajola, M., Besse, S., Davidsson, Björn J. R., Lara, L. M., Mottola, S., Naletto, G., Sierks, H., Barucci, A. M., Scholten, F., Preusker, F., Pommerol, A., Masoumzadeh, N., Lazzarin, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H., Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuehrt, E., Kueppers, M., Lin, Z. -Y., Lopez Moreno, J. J., Marzari, F., Moreno, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Oklay, N., Vincent, J. -B, Fornasier, S., Pajola, M., Besse, S., Davidsson, Björn J. R., Lara, L. M., Mottola, S., Naletto, G., Sierks, H., Barucci, A. M., Scholten, F., Preusker, F., Pommerol, A., Masoumzadeh, N., Lazzarin, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H., Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuehrt, E., Kueppers, M., Lin, Z. -Y., Lopez Moreno, J. J., Marzari, F., Moreno, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Abstract

Aims. We carried out an investigation of the surface variegation of comet 67P/Churyumov-Gerasimenko, the detection of regions showing activity, the determination of active and inactive surface regions of the comet with spectral methods, and the detection of fallback material. Methods. We analyzed multispectral data generated with Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) observations via spectral techniques, reflectance ratios, and spectral slopes in order to study active regions. We applied clustering analysis to the results of the reflectance ratios, and introduced the new technique of activity thresholds to detect areas potentially enriched in volatiles. Results. Local color inhomogeneities are detected over the investigated surface regions. Active regions, such as Hapi, the active pits of Seth and Ma'at, the clustered and isolated bright features in Imhotep, the alcoves in Seth and Ma'at, and the large alcove in Anuket, have bluer spectra than the overall surface. The spectra generated with OSIRIS NAC observations are dominated by cometary emissions of around 700 nm to 750 nm as a result of the coma between the comet's surface and the camera. One of the two isolated bright features in the Imhotep region displays an absorption band of around 700 nm, which probably indicates the existence of hydrated silicates. An absorption band with a center between 800-900 nm is tentatively observed in some regions of the nucleus surface. This absorption band can be explained by the crystal field absorption of Fe2+, which is a common spectral feature seen in silicates.

Published
2016
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23. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

Author

Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.

Abstract

Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance R-h = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 mu m) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 x 10(13) and 8.5 x 10(10) for a = 5 and 50 mu m, respectively, or an initial mass of H2O ice around 22 kg.

Published
2016
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24. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations

Author

Feller, C., primary, Fornasier, S., additional, Hasselmann, P. H., additional, Barucci, A., additional, Preusker, F., additional, Scholten, F., additional, Jorda, L., additional, Pommerol, A., additional, Jost, B., additional, Poch, O., additional, ElMaary, M. R., additional, Thomas, N., additional, Belskaya, I., additional, Pajola, M., additional, Sierks, H., additional, Barbieri, C., additional, Lamy, P. L., additional, Koschny, D., additional, Rickman, H., additional, Rodrigo, R., additional, Agarwal, J., additional, A’Hearn, M., additional, Bertaux, J.-L., additional, Bertini, I., additional, Boudreault, S., additional, Cremonese, G., additional, Da Deppo, V., additional, Davidsson, B. J. R., additional, Debei, S., additional, De Cecco, M., additional, Deller, J., additional, Fulle, M., additional, Giquel, A., additional, Groussin, O., additional, Gutierrez, P. J., additional, Güttler, C., additional, Hofmann, M., additional, Hviid, S. F., additional, Keller, H., additional, Ip, W.-H., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Kührt, E., additional, Küppers, M., additional, Lara, M. L., additional, Lazzarin, M., additional, Leyrat, C., additional, Lopez Moreno, J. J., additional, Marzari, F., additional, Masoumzadeh, N., additional, Mottola, S., additional, Naletto, G., additional, Perna, D., additional, Oklay, N., additional, Shi, X., additional, Tubiana, C., additional, and Vincent, J.-B., additional

Published
2016
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25. Sublimation of icy aggregates in the coma of comet 67P/Churyumov–Gerasimenko detected with the OSIRIS cameras on boardRosetta

Author

Gicquel, A., primary, Vincent, J.-B., additional, Agarwal, J., additional, A'Hearn, M. F., additional, Bertini, I., additional, Bodewits, D., additional, Sierks, H., additional, Lin, Z.-Y., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, Keller, H. U., additional, Barucci, M. A., additional, Bertaux, J.-L., additional, Besse, S., additional, Cremonese, G., additional, Da Deppo, V., additional, Davidsson, B., additional, Debei, S., additional, Deller, J., additional, De Cecco, M., additional, Frattin, E., additional, El-Maarry, M. R., additional, Fornasier, S., additional, Fulle, M., additional, Groussin, O., additional, Gutiérrez, P. J., additional, Gutiérrez-Marquez, P., additional, Güttler, C., additional, Höfner, S., additional, Hofmann, M., additional, Hu, X., additional, Hviid, S. F., additional, Ip, W.-H., additional, Jorda, L., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Kührt, E., additional, Küppers, M., additional, Lara, L. M., additional, Lazzarin, M., additional, Moreno, J. J. Lopez, additional, Lowry, S., additional, Marzari, F., additional, Masoumzadeh, N., additional, Massironi, M., additional, Moreno, F., additional, Mottola, S., additional, Naletto, G., additional, Oklay, N., additional, Pajola, M., additional, Pommerol, A., additional, Preusker, F., additional, Scholten, F., additional, Shi, X., additional, Thomas, N., additional, Toth, I., additional, and Tubiana, C., additional

Published
2016
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26. Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Author

Oklay, N., primary, Vincent, J.-B., additional, Fornasier, S., additional, Pajola, M., additional, Besse, S., additional, Davidsson, B. J. R., additional, Lara, L. M., additional, Mottola, S., additional, Naletto, G., additional, Sierks, H., additional, Barucci, A. M., additional, Scholten, F., additional, Preusker, F., additional, Pommerol, A., additional, Masoumzadeh, N., additional, Lazzarin, M., additional, Barbieri, C., additional, Lamy, P. L., additional, Rodrigo, R., additional, Koschny, D., additional, Rickman, H., additional, A’Hearn, M. F., additional, Bertaux, J.-L., additional, Bertini, I., additional, Bodewits, D., additional, Cremonese, G., additional, Da Deppo, V., additional, Debei, S., additional, De Cecco, M., additional, Fulle, M., additional, Groussin, O., additional, Gutiérrez, P. J., additional, Güttler, C., additional, Hall, I., additional, Hofmann, M., additional, Hviid, S. F., additional, Ip, W.-H., additional, Jorda, L., additional, Keller, H. U., additional, Knollenberg, J., additional, Kovacs, G., additional, Kramm, J.-R., additional, Kührt, E., additional, Küppers, M., additional, Lin, Z.-Y., additional, Lopez Moreno, J. J., additional, Marzari, F., additional, Moreno, F., additional, Shi, X., additional, Thomas, N., additional, Toth, I., additional, and Tubiana, C., additional

Published
2016
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27. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations

Author

Fornasier, S., Debei, S., Jorda, L., Lazzarin, M., Mottola, S., Hofmann, M., Ip, W.-H., Tubiana, C., Rodrigo, R., Leyrat, C., Thomas, Nicolas, Belskaya, I., Agarwal, J., Küppers, M., Poch, Olivier, Hviid, S. F., Masoumzadeh, N., Sierks, H., Giquel, A., Preusker, F., De Cecco, M., Kramm, J.-R., Bertini, I., Barbieri, C., Vincent, J.-B., Da Deppo, V., Naletto, G., Oklay, N., Rickman, H., Bertaux, J.-L., Pajola, M., Keller, H., Güttler, C., Lopez Moreno, J. J., Barucci, A., Kovacs, G., Koschny, D., Pommerol, Antoine, Gutierrez, P. J., ElMaary, M. R., Scholten, F., Cremonese, G., Perna, D., Marzari, F., A’Hearn, M., Lamy, P. L., Groussin, O., Shi, X., Kührt, E., Feller, C., Jost, Bernhard, Davidsson, B. J. R., Lara, M. L., Boudreault, S., Deller, J., Fulle, M., Knollenberg, J., and Hasselmann, P. H.

Subjects
13. Climate action, 530 Physics, 520 Astronomy, 620 Engineering
Abstract

We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the OSIRIS instrument during the closest fly-by over the comet, which took place on 14 th February 2015 at a distance of ~ 6 km from the surface. Several images covering the 033° phase angle range were acquired, and the spatial resolution achieved was 11 cm/pxl. The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40% between bright spots and sombre regions, and spectral slope variations up to 50%. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our dataset using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8%) and it has a high porosity value in the uppermost-layers (86%). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.

28. Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Author

Besse, S., Bertaux, J. L., Debei, S., Cremonese, G., Marzari, F., Hall, I., Preusker, F., Groussin, O., Pommerol, Antoine, Kovacs, G., Sierks, H., Thomas, Nicolas, Da Deppo, V., Davidsson, B. J. R., Lara, L. M., Scholten, F., Lazzarin, M., Gutierrez, P. J., Hofmann, M., Keller, H. U., Jorda, L., Moreno, F., Kueppers, M., Bertini, I., Toth, I., Vincent, J. B., Rickman, H., Oklay, N., Lamy, P. L., Barucci, A. M., Hviid, S. F., Tubiana, C., Barbieri, C., Fulle, M., De Cecco, M., Ip, W. H., A'Hearn, M. F., Kuehrt, E., Knollenberg, J., Naletto, G., Shi, X., Fornasier, S., Kramm, J. R., Bodewits, D., Rodrigo, R., Lopez Moreno, J. J., Koschny, D., Lin, Z. Y., Guettler, C., Pajola, M., Mottola, S., and Masoumzadeh, N.

Subjects
13. Climate action, 530 Physics, 520 Astronomy
Abstract

Aims. We carried out an investigation of the surface variegation of comet 67P/Churyumov-Gerasimenko, the detection of regions showing activity, the determination of active and inactive surface regions of the comet with spectral methods, and the detection of fallback material. Methods. We analyzed multispectral data generated with Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) observations via spectral techniques, reflectance ratios, and spectral slopes in order to study active regions. We applied clustering analysis to the results of the reflectance ratios, and introduced the new technique of activity thresholds to detect areas potentially enriched in volatiles. Results. Local color inhomogeneities are detected over the investigated surface regions. Active regions, such as Hapi, the active pits of Seth and Ma'at, the clustered and isolated bright features in Imhotep, the alcoves in Seth and Ma'at, and the large alcove in Anuket, have bluer spectra than the overall surface. The spectra generated with OSIRIS NAC observations are dominated by cometary emissions of around 700 nm to 750 nm as a result of the coma between the comet's surface and the camera. One of the two isolated bright features in the Imhotep region displays an absorption band of around 700 nm, which probably indicates the existence of hydrated silicates. An absorption band with a center between 800-900 nm is tentatively observed in some regions of the nucleus surface. This absorption band can be explained by the crystal field absorption of Fe2+, which is a common spectral feature seen in silicates.

29. Modelling of the outburst on 2015 July 29 observed with OSIRIS cameras in the Southern hemisphere of comet 67P/Churyumov–Gerasimenko

Author

De Cecco, M., Debei, S., Gutiérrez, P. J., Rodrigo, Rafael, Moreno, F., Groussin, O., Sierks, H., Keller, H. U., Barbieri, C., Da Deppo, V., Bertaux, J.-L., Lamy, P. L., Mottola, S., Hu, X., Kührt, E., Kramm, J.-R., Rickman, H., Agarwal, J., Lin, Z.-Y., Davidsson, B., Lazzarin, M., Gutiérrez-Marquez, P., Höfner, S., Oklay, N., Gicquel, A., Shi, X., Massironi, M., Jorda, L., Deller, J., Güttler, C., Ip, W.-H., Cremonese, G., Rose, M., Toth, I., Hofmann, M., Küppers, M., Lara, L. M., Kovacs, G., Fulle, M., Masoumzadeh, N., Knollenberg, J., El-Maarry, M. R., Vincent, J.-B., Fornasier, S., Fougere, N., Thomas, Nicolas, Scholten, F., Boudreault, S., Hviid, S. F., Lowry, S., Tubiana, C., Frattin, E., Pajola, M., A’Hearn, M. F., Koschny, D., Bertini, I., Marzari, F., Bodewits, D., Preusker, F., Barucci, M. A., Naletto, G., Moreno, J. J. Lopez, and Besse, S.

Subjects
13. Climate action, 520 Astronomy, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, 620 Engineering, Astrophysics::Galaxy Astrophysics
Abstract

Images of the nucleus and the coma (gas and dust) of comet 67P/Churyumov– Gerasimenko have been acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) cameras since 2014 March using both the wide-angle camera and the narrow-angle camera (NAC). We use images from the NAC camera to study a bright outburst observed in the Southern hemisphere on 2015 July 29. The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus. The heliocentric distance is 1.25 au and the spacecraft–comet distance is 186 km. Aiming to better understand the physics that led to the outgassing, we used the Direct Simulation Monte Carlo method to study the gas flow close to the nucleus and the dust trajectories. The goal is to understand the mechanisms producing the outburst. We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region. The outburst is in fact a combination of both gas and dust, in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas. We need a number of dust particles 7.83 × 1011 to 6.90 × 1015 (radius 1.97–185 μm), which correspond to a mass of dust (220–21) × 103 kg.

30. Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Author

Davidsson, B. J. R., Feller, C., Tubiana, C., Preusker, F., Keller, H. U., Bertini, I., Barucci, M. A., Lopez Moreno, J. J., Sierks, H., Kolokolova, L., Rickman, H., Knollenberg, J., Barbieri, C., Thomas, Nicolas, Shi, X., Marzari, F., Fornasier, S., Debei, S., Hviid, S. F., Scholten, F., Lazzarin, M., De Cecco, M., Cremonese, G., Fulle, M., Kramm, J.-R., Masoumzadeh, N., Bertaux, J.-L., Jorda, L., Mottola, S., Rodrigo, Rafael, Gicquel, A., Da Deppo, V., Küppers, M., Kührt, E., A’Hearn, M. F., Hall, I., Hofmann, M., Vincent, J.-B., Lamy, P. L., Lara, L. M., Naletto, G., Oklay, N., Groussin, O., Koschny, D., Gutiérrez, P. J., Kovacs, G., Ip, W.-H., Güttler, C., and Hasselmann, P. H.

Subjects
13. Climate action, 520 Astronomy, 620 Engineering
Abstract

We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.

31. Exposed bright features on the comet 67P/Churyumov–Gerasimenko: distribution and evolution

Author

Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Hasselmann, P. H., Feller, C., Sierks, H., Lucchetti, A., Pajola, M., Oklay, N., Mottola, S., Masoumzadeh, N., Tubiana, C., Güttler, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Bertaux, J.-L., Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Cecco, M. De, Deller, J., Fulle, M., Groussin, O., Gutierrez, P. J., Hoang, H. V., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kührt, E., Küppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Preusker, F., Shi, X., Thomas, Nicolas, and Vincent, J.-B.

Subjects
13. Climate action, 520 Astronomy, 620 Engineering
Abstract

Context. Since its arrival at the comet 67P/Churyumov–Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta. Aims. We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance. Methods. We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel–Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest. Results. We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of H2O ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category. Conclusions. Although the nucleus of 67P/Churyumov–Gerasimenko appears to be dark in general, there are localised H2O ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated H2O ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet’s return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated H2O ice that is preserved with consolidated cometary material, as observed on exposed patches resting on boulders. This is corroborated by our albedo calculations that attribute higher albedos for bright features with formations related to outbursts.

32. Long-term survival of surface water ice on comet 67P

Author

Oklay, N., Mottola, S., Vincent, J.-B., Pajola, M., Fornasier, S., Hviid, S. F., Kappel, D., Kührt, E., Keller, H. U., Barucci, M. A., Feller, C., Preusker, F., Scholten, F., Hall, I., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., A’Hearn, M. F., Bertaux, J.-L., Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, P. J., Güttler, C., Hasselmann, P. H., Hofmann, M., Ip, W.-H., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J.-R., Küppers, M., Lara, L. M., Lazzarin, M., Lin, Z.-Y., Moreno, J. J. Lopez, Lucchetti, A., Marzari, F., Masoumzadeh, N., Naletto, G., Pommerol, Antoine, Shi, X., Thomas, Nicolas, and Tubiana, C.

Subjects
13. Climate action, 520 Astronomy, 620 Engineering
Abstract

Numerous water-ice-rich deposits surviving more than several months on comet 67P/Churyumov-Gerasimenko were observed during the Rosetta mission. We announce the first-time detection of water-ice features surviving up to 2 yr since their first observation via OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) NAC (narrow angle camera). Their existence on the nucleus of comet 67P at the arrival of the Rosetta spacecraft suggests that they were exposed to the surface during the comet’s previous orbit. We investigated the temporal variation of large water-ice patches to understand the long-term sustainability of water ice on cometary nuclei on time-scales of months and years. Large clusters are stable over typical periods of 0.5 yr and reduce their size significantly around the comet’s perihelion passage, while small exposures disappear. We characterized the temporal variation of their multispectral signatures. In large clusters, dust jets were detected, whereas in large isolated ones no associated activity was detected. Our thermal analysis shows that the long-term sustainability of water-ice-rich features can be explained by the scarce energy input available at their locations over the first half year. However, the situation reverses for the period lasting several months around perihelion passage. Our two end-member mixing analysis estimates a pure water-ice equivalent thickness up to 15 cm within one isolated patch, and up to 2 m for the one still observable through the end of the mission. Our spectral modelling estimates up to 48 per cent water-ice content for one of the large isolated feature, and up to 25 per cent water ice on the large boulders located within clusters.

33. Rapid spread and high mortality due to community-acquired pneumonia caused by Acinetobacter baumannii (CAP-AB) in a Covid-19 intensive care unit.

Author

Shafigh N, Roodneshin F, Shafigh E, Kermany MPZN, Ziaie S, Miller J, Gharehbeglou M, Masoumzadeh N, Hasheminik M, and Avval JO

Abstract

Acinetobacter baumannii is a rare but dangerous gram-negative bacteria causing nosocomial infections, especially in intensive care units. The increased use of antibiotics in the treatment of bacterial infections leads to drug resistance, delays, or failures in treatment. The patient is a 48-year-old man with coronavirus disease (COVID-19) being treated in the intensive care unit. After contracting Acinetobacter baumannii , the patient's condition deteriorated, and he developed severe pulmonary problems. Due to the unknown presence of Acinetobacter baumannii in the patient, this bacterium transmitted to six other patients in the ward, which resulted in their deaths. In this report, we describe the causes and risk factors of the disease, and the results of laboratory tests and therapeutic processes., Competing Interests: There are no conflicts of interest., (Copyright: © 2023 Journal of Family Medicine and Primary Care.)

Published
2022
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34. Magnesium supplementation and insulin resistance in patients with rheumatoid arthritis.

Author

Norouzi M, Rezvankhah B, Haeri MR, Heydari H, Tafaroji J, Shafigh N, Avval JO, Dahmardeh AR, Masoumzadeh N, and Gharehbeglou M

Abstract

Rheumatoid arthritis (RA) is a multifactorial disease affecting the immune system and many tissues in the body. This study aimed to evaluate the effect of magnesium supplementation on insulin resistance and fasting blood sugar (FBS) of patients with RA. In this prospective uncontrolled before-after study, RA patients referring to Rheumatology clinics of Qom City from January 2020 to January 2021 were evaluated. First, the patients received the routine rheumatoid arthritis treatment including 5 mg Prednisolone and 200mg Hydroxychloroquine daily for 6 months and FBS and insulin levels were measured after. Then, they received the routine arthritis rheumatoid treatment in addition to 300 mg/day oral Magnesium sulfate for 6 months and then, FBS and insulin levels were measured. The Homeostasis Model Assessment of insulin resistance (HOMA-IR) was used for determining insulin resistance. Thirty five patients with RA and the mean age of 49.83±2.58 years were enrolled. Twenty eight cases (80%) were female and 7 cases (20%) were male. The mean HOMA-IR before and after consumption of oral magnesium were 3.04±0.29 and 2.43±0.19, respectively. Statistically significant differences were found between FBS, insulin and HOMA-IR before and after consumption of oral magnesium (p<0.05). Our data suggested that magnesium supplementation reduces FBS, insulin and HOMA-IR in patients with rheumatoid arthritis. Thus, magnesium supplements may be an alternative method for prevention of type 2 diabetes in RA patients.

Published
2022
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