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Davidsson, Björn
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Publications (10 of 72) Show all publications
Lai, I.-L., Ip, W.-H., Lee, J.-C., Lin, Z. Y., Vincent, J.-B., Oklay, N., . . . Thomas, N. (2019). Seasonal variations in source regions of the dust jets on comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 630, Article ID A17.
Open this publication in new window or tab >>Seasonal variations in source regions of the dust jets on comet 67P/Churyumov-Gerasimenko
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A17Article in journal (Refereed) Published
Abstract [en]

Aims: We investigate the surface distribution of the source regions of dust jets on comet 67P/Churyumov-Gerasimenko as a function of time.

Methods: The dust jet source regions were traced by the comprehensive imaging data set provided by the OSIRIS scientific camera.

Results: We show in detail how the projected footpoints of the dust jets and hence the outgassing zone would move in consonance with the sunlit belt. Furthermore, a number of source regions characterized by repeated jet activity might be the result of local topographical variations or compositional heterogeneities.

Conclusions: The spatial and temporal variations in source regions of the dust jets are influenced significantly by the seasonal effect. The strong dependence on the solar zenith angle and local time could be related to the gas sublimation process driven by solar insolation on a surface layer of low thermal inertia.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2019
Keywords
comets: individual: 67P/Churyumov-Gerasimenko
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-395682 (URN)10.1051/0004-6361/201732094 (DOI)000486989400017 ()
Funder
Swedish National Space Board
Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Lin, Z.-Y., Knollenberg, J., Vincent, J.-B. -., A'Hearn, M. F., Ip, W.-H., Sierks, H., . . . Tubiana, C. (2017). Investigating the physical properties of outbursts on comet 67P/Churyumov-Gerasimenko. Paper presented at International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE. Monthly notices of the Royal Astronomical Society, 469, S731-S740
Open this publication in new window or tab >>Investigating the physical properties of outbursts on comet 67P/Churyumov-Gerasimenko
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S731-S740Article in journal (Refereed) Published
Abstract [en]

Cometary outbursts on several comets have been observed both by ground-based telescopes and by in situ instruments on spacecraft. However, the mechanism behind these phenomena and their physical properties are still unclear. The optical, spectrocopic and infrared remote imaging system (OSIRIS) onboard the Rosetta spacecraft provided first-hand information on the outbursts from comet 67P/Churyumov-Gerasimenko during its perihelion passage in 2015. The physical properties of the outbursts can be investigated by examining the time series of these high-resolution images. An analysis is made of the wide- and narrow-angle images obtained during the monitoring of the outburst sequences, which occurred between July and September in 2015. A ring-masking technique is used to calculate the excess brightness of the outbursts. The ejected mass and expansion velocity of the outbursts is estimated from differences in images made with the same filter (orange filter). The calculated excess brightness from these outburst plumes ranges from a few per cent to 28 per cent. In some major outbursts, the brightness contribution from the outburst plume can be one or two times higher than that of the typical coma jet activities. The strongest event was the perihelion outburst detected just a few hours before perihelion. The mass ejection rate during a generic outburst could reach a few per cent of the steady-state value of the dust coma. Transient events are detected by studying the brightness slope of the outburst plume with continuous streams of outflowing gas and dust triggered by driving mechanisms, as yet not understood, which remain active for several minutes to less than a few hours.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
comets: individual: 67P/Churyumov-Gerasimenko
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-376697 (URN)10.1093/mnras/stx2768 (DOI)000443940500065 ()
Conference
International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE
Available from: 2019-02-13 Created: 2019-02-13 Last updated: 2019-02-13Bibliographically approved
Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M. A., . . . Thomas, N. (2017). Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images. Astronomy and Astrophysics, 599, Article ID A11.
Open this publication in new window or tab >>Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, article id A11Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2017
Keywords
planets and satellites: surfaces, techniques: photometric, comets: individual: 67P/Churyumov, Gerasimenko
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-320264 (URN)10.1051/0004-6361/201629734 (DOI)000395821900094 ()
Funder
Swedish National Space Board
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2017-04-18Bibliographically approved
Frattin, E., Cremonese, G., Simioni, E., Bertini, I., Lazzarin, M., Ott, T., . . . Vincent, J.-B. -. (2017). Post-perihelion photometry of dust grains in the coma of 67P Churyumov-Gerasimenko. Paper presented at International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE. Monthly notices of the Royal Astronomical Society, 469, S195-S203
Open this publication in new window or tab >>Post-perihelion photometry of dust grains in the coma of 67P Churyumov-Gerasimenko
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S195-S203Article in journal (Refereed) Published
Abstract [en]

We present a photometric analysis of individual dust grains in the coma of comet 67P/Churyumov-Gerasimenko using OSIRIS images taken from 2015 July to 2016 January. We analysed a sample of 555 taken during 18 d at heliocentric distances ranging between 1.25 and 2.04 au and at nucleocentric distances between 80 and 437 km. An automated method to detect the tracks was specifically developed. The images were taken by OSIRIS NAC in four different filters: Near-IR (882 nm), Orange (649 nm), FarOrange (649 nm) and Blue (480 nm). It was not always possible to recognize all the grains in the four filters, hence we measured the spectral slope in two wavelengths ranges: in the interval [480-649] nm, for 1179 grains, and in the interval [649-882] nm, for 746 grains. We studied the evolution of the two populations' average spectral slopes. The data result scattered around the average value in the range [480-649] nm, while in the [649-882] nm we observe a slight decreasing moving away from the Sun as well as a slight increasing with the nucleocentric distance. A spectrophotometric analysis was performed on a subsample of 339 grains. Three major groups were defined, based on the spectral slope between [535-882] nm: (i) the steep spectra that may be related with organic material, (ii) the spectra with an intermediate slope, likely a mixture of silicates and organics and (iii) flat spectra that may be associated with a high abundance of water ice.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
methods: data analysis, techniques: photometric, comets: general, zodiacal dust
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-376685 (URN)10.1093/mnras/stx1395 (DOI)000443940500018 ()
Conference
International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE
Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-02-15Bibliographically approved
Keller, H. U., Mottola, S., Hviid, S. F., Agarwal, J., Kuehrt, E., Skorov, Y., . . . Thomas, N. (2017). Seasonal mass transfer on the nucleus of comet 67P/Chuyumov-Gerasimenko. Paper presented at International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE. Monthly notices of the Royal Astronomical Society, 469, S357-S371
Open this publication in new window or tab >>Seasonal mass transfer on the nucleus of comet 67P/Chuyumov-Gerasimenko
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S357-S371Article in journal (Refereed) Published
Abstract [en]

We collect observational evidence that supports the scheme of mass transfer on the nucleus of comet 67P/Churyumov-Gerasimenko. The obliquity of the rotation axis of 67P causes strong seasonal variations. During perihelion the southern hemisphere is four times more active than the north. Northern territories are widely covered by granular material that indicates back fall originating from the active south. Decimetre sized chunks contain water ice and their trajectories are influenced by an antisolar force instigated by sublimation. OSIRIS observations suggest that up to 20 per cent of the particles directly return to the nucleus surface taking several hours of traveltime. The back fall covered northern areas are active if illuminated but produce mainly water vapour. The decimetre chunks from the nucleus surface are too small to contain more volatile compounds such as CO2 or CO. This causes a north-south dichotomy of the composition measurements in the coma. Active particles are trapped in the gravitational minimum of Hapi during northern winter. They are 'shock frozen' and only re-activated when the comet approaches the sun after its aphelion passage. The insolation of the big cavity is enhanced by self-heating, i.e. reflection and IR radiation from the walls. This, together with the pristinity of the active back fall, explains the early observed activity of the Hapi region. Sobek may be a role model for the consolidated bottom of Hapi. Mass transfer in the case of 67P strongly influences the evolution of the nucleus and the interpretation of coma measurements.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
methods: data analysis, comets: individual (67P/Churyumov-Gerasimenko)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-376696 (URN)10.1093/mnras/stx1726 (DOI)000443940500035 ()
Conference
International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE
Funder
EU, Horizon 2020, 686709Swedish National Space Board
Available from: 2019-02-08 Created: 2019-02-08 Last updated: 2019-02-08Bibliographically approved
Preusker, F., Scholten, F., Matz, K.-D. -., Roatsch, T., Hviid, S. F., Mottola, S., . . . Tubiana, C. (2017). The global meter-level shape model of comet 67P/Churyumov-Gerasimenko [Letter to the editor]. Astronomy and Astrophysics, 607, Article ID L1.
Open this publication in new window or tab >>The global meter-level shape model of comet 67P/Churyumov-Gerasimenko
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 607, article id L1Article in journal, Letter (Refereed) Published
Abstract [en]

We performed a stereo-photogrammetric (SPG) analysis of more than 1500 Rosetta/OSIRIS NAC images of comet 67P/ChuryumovGerasimenko (67P). The images with pixel scales in the range 0.2-3.0 m/pixel were acquired between August 2014 and February 2016. We finally derived a global high-resolution 3D description of 67P's surface, the SPG SHAP7 shape model. It consists of about 44 million facets (1-1.5 m horizontal sampling) and a typical vertical accuracy at the decimeter scale. Although some images were taken after perihelion, the SPG SHAP7 shape model can be considered a pre-perihelion description and replaces the previous SPG SHAP4S shape model. From the new shape model, some measures for 67P with very low 3 sigma uncertainties can be retrieved: 18.56 km(3) +/- 0 : 02 km(3) for the volume and 537.8 kg/m(3) +/- 0.7 kg/m(3) for the mean density assuming a mass value of 9 : 982 +/- 10(12) kg.

Keywords
methods: data analysis, techniques: image processing, comets: individual: 67P/Churyumov Gerasimenko, planets and satellites: surfaces
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-341359 (URN)10.1051/0004-6361/201731798 (DOI)000414181900001 ()
Funder
EU, Horizon 2020, 686709
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-02-12Bibliographically approved
Höfner, S., Vincent, J.-B. -., Blum, J., Davidsson, B. J. R., Sierks, H., El-Maarry, M. R., . . . Zitzmann, S. (2017). Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 608, Article ID A121.
Open this publication in new window or tab >>Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 608, article id A121Article in journal (Refereed) Published
Abstract [en]

Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain.

Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods.

Methods. We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain.

Results. Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P.

Conclusions. At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m2 and trigger dust activity that can be related mainly to H2O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue.

Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, radiation mechanisms: thermal
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-339793 (URN)10.1051/0004-6361/201628726 (DOI)000418458600015 ()
Funder
Swedish National Space Board
Available from: 2018-02-23 Created: 2018-02-23 Last updated: 2018-02-23Bibliographically approved
Knollenberg, J., Lin, Z. Y., Hviid, S. F., Oklay, N., Vincent, J.-B. -., Bodewits, D., . . . Tubiana, C. (2016). A mini outburst from the nightside of comet 67P/Churyumov-Gerasimenko observed by the OSIRIS camera on Rosetta. Astronomy and Astrophysics, 596, Article ID A89.
Open this publication in new window or tab >>A mini outburst from the nightside of comet 67P/Churyumov-Gerasimenko observed by the OSIRIS camera on Rosetta
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A89Article in journal (Refereed) Published
Abstract [en]

Context. On 12 March 2015 the OSIRIS WAC camera onboard the ESA Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko observed a small outburst originating from the Imhotep region at the foot of the big lobe of the comet. These measurements are unique since it was the first time that the initial phase of a transient outburst event could be directly observed. Aims. We investigate the evolution of the dust jet in order to derive clues about the outburst source mechanism and the ejected dust particles, in particular the dust mass, dust-to-gas ratio and the particle size distribution. Methods. Analysis of the images and of the observation geometry using comet shape models in combination with gasdynamic modeling of the transient dust jet were the main tools used in this study. Synthetic images were computed for comparison with the observations. Results. Analysis of the geometry revealed that the source region was not illuminated until 1.5 h after the event implying true nightside activity was observed. The outburst lasted for less than one hour and the average dust production rate during the initial four minutes was of the order of 1 kg/s. During this time the outburst dust production rate was approximately constant, no sign for an initial explosion could be detected. For dust grains between 0.01-1 mm a power law size distribution characterized by an index of about 2.6 provides the best fit to the observed radiance profiles. The dust-to-gas ratio of the outburst jet is in the range 0.6-1.8.

Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, methods: numerical
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-315081 (URN)10.1051/0004-6361/201527744 (DOI)000390797900010 ()
Available from: 2017-02-09 Created: 2017-02-09 Last updated: 2017-11-29Bibliographically approved
Vincent, J.-B. -., Oklay, N., Pajola, M., Hoefner, S., Sierks, H., Hu, X., . . . Tubiana, C. (2016). Are fractured cliffs the source of cometary dust jets?: Insights from OSIRIS/Rosetta at 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 587, Article ID A14.
Open this publication in new window or tab >>Are fractured cliffs the source of cometary dust jets?: Insights from OSIRIS/Rosetta at 67P/Churyumov-Gerasimenko
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A14Article in journal (Refereed) Published
Abstract [en]

Context: Dust jets (i.e., fuzzy collimated streams of cometary material arising from the nucleus) have been observed in situ on all comets since the Giotto mission flew by comet 1P/Halley in 1986, and yet their formation mechanism remains unknown. Several solutions have been proposed involving either specific properties of the active areas or the local topography to create and focus the gas and dust flows. While the nucleus morphology seems to be responsible for the larger features, high resolution imagery has shown that broad streams are composed of many smaller jets (a few meters wide) that connect directly to the nucleus surface.

Aims: We monitored these jets at high resolution and over several months to understand what the physical processes are that drive their formation and how this affects the surface.

Methods: Using many images of the same areas with different viewing angles, we performed a 3-dimensional reconstruction of collimated jets and linked them precisely to their sources on the nucleus.

Results: We show here observational evidence that the northern hemisphere jets of comet 67P/Churyumov-Gerasimenko arise from areas with sharp topographic changes and describe the physical processes involved. We propose a model in which active cliffs are the main source of jet-like features and therefore of the regions eroding the fastest on comets. We suggest that this is a common mechanism taking place on all comets.

Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-295586 (URN)10.1051/0004-6361/201527159 (DOI)000371589800025 ()
Funder
Swedish National Space Board
Available from: 2016-06-08 Created: 2016-06-08 Last updated: 2017-11-30Bibliographically approved
Bodewits, D., Lara, L. M., A'Hearn, M. F., La Forgia, F., Gicquel, A., Kovacs, G., . . . Vincent, J.-B. -. (2016). Changes in the physical environment of the inner coma of 67p/churyumov-gerasimenko with decreasing heliocentric distance. Astronomical Journal, 152(5), Article ID 130.
Open this publication in new window or tab >>Changes in the physical environment of the inner coma of 67p/churyumov-gerasimenko with decreasing heliocentric distance
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2016 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 152, no 5, article id 130Article in journal (Refereed) Published
Abstract [en]

The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrow-band filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and heliocentric distance, here between 2.6 and 1.3 au pre-perihelion. Our observations indicate that the emission observed in the OH, OI, CN, NH, and NH2 filters is mostly produced by dissociative electron impact excitation of different parent species. We conclude that CO2 rather than H2O is a significant source of the [OI] 630 nm emission. A strong plume-like feature observed in the CN and OI filters is present throughout our observations. This plume is not present in OH emission and indicates a local enhancement of the CO2/H2O ratio by as much as a factor of 3. We observed a sudden decrease in intensity levels after 2015 March, which we attribute to decreased electron temperatures in the first few kilometers above the surface of the nucleus.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
Keywords
atomic processes, comets: individual (67P/Churyumov-Gerasimenko), molecular processes, plasmas, radiation mechanisms: non-thermal, techniques: image processing
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-319897 (URN)10.3847/0004-6256/152/5/130 (DOI)000395998800001 ()
Funder
Swedish National Space Board
Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-20Bibliographically approved
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