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382 results on '"Keller, H.U."'

1. Regional unit definition for the nucleus of comet 67P/Churyumov-Gerasimenko on the SHAP7 model

Author

Thomas, N., El Maarry, M.R., Theologou, P., Preusker, F., Scholten, F., Jorda, L., Hviid, S.F., Marschall, R., Kührt, E., Naletto, G., Sierks, H., Lamy, P.L., Rodrigo, R., Koschny, D., Davidsson, B., Barucci, M.A., Bertaux, J.L., Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutièrrez, P.J., Güttler, C., Ip, W.H., Keller, H.U., Knollenberg, J., Lara, L.M., Lazzarin, M., Lòpez-Moreno, J.J., Marzari, F., Tubiana, C., and Vincent, J.B.

Published
2018
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3. On deviations from free-radial outflow in the inner coma of comet 67P/Churyumov–Gerasimenko

Author

Gerig, S.-B., Marschall, R., Thomas, N., Bertini, I., Bodewits, D., Davidsson, B., Fulle, M., Ip, W.-H., Keller, H.U., Küppers, M., Preusker, F., Scholten, F., Su, C.C., Toth, I., Tubiana, C., Wu, J.-S., Sierks, H., Barbieri, C., Lamy, P.L., Rodrigo, R., Koschny, D., Rickman, H., Agarwal, J., Barucci, M.A., Bertaux, J.-L., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P.J., Güttler, C., Hviid, S.F., Jorda, L., Knollenberg, J., Kramm, J.-R., Kührt, E., Lara, L.M., Lazzarin, M., Lopez Moreno, J.J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., and Vincent, J.-B.

Published
2018
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4. Meter-scale thermal contraction crack polygons on the nucleus of comet 67P/Churyumov-Gerasimenko

Author

Auger, A.-T., Groussin, O., Jorda, L., El-Maarry, M.R., Bouley, S., Séjourné, A., Gaskell, R., Capanna, C., Davidsson, B., Marchi, S., Höfner, S., Lamy, P.L., Sierks, H., Barbieri, C., Rodrigo, R., Koschny, D., Rickman, H., Keller, H.U., Agarwal, J., A’Hearn, M.F., Barucci, M.A., Bertaux, J.-L., Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Gutiérrez, P.J., Güttler, C., Hviid, S., Ip, W.-H., Knollenberg, J., Kramm, J.-R., Kührt, E., Küppers, M., Lara, L.M., Lazzarin, M., Lopez Moreno, J.J., Marzari, F., Massironi, M., Michalik, H., Naletto, G., Oklay, N., Pommerol, A., Sabau, L., Thomas, N., Tubiana, C., Vincent, J.-B., and Wenzel, K.-P.

Published
2018
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5. Distance determination method of dust particles using Rosetta OSIRIS NAC and WAC data

Author

Drolshagen, E., Ott, T., Koschny, D., Güttler, C., Tubiana, C., Agarwal, J., Sierks, H., Barbieri, C., Lamy, P.I., Rodrigo, R., Rickman, H., A'Hearn, M.F., Barucci, M.A., Bertaux, J.-L., Bertini, I., Cremonese, G., Deppo, V. Da, Davidsson, B., Debei, S., Cecco, M. De, Deller, J., Feller, C., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, P.J., Hofmann, M., Hviid, S.F., Ip, W.-H., Jorda, L., Keller, H.U., Knollenberg, J., Kramm, J.R., Kührt, E., Küppers, M., Lara, L.M., Lazzarin, M., Moreno, J.J. Lopez, Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., and Poppe, B.

Published
2017
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8. The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations

Author

Jorda, L., Gaskell, R., Capanna, C., Hviid, S., Lamy, P., Ďurech, J., Faury, G., Groussin, O., Gutiérrez, P., Jackman, C., Keihm, S.J., Keller, H.U., Knollenberg, J., Kührt, E., Marchi, S., Mottola, S., Palmer, E., Schloerb, F.P., Sierks, H., Vincent, J.-B., A’Hearn, M.F., Barbieri, C., Rodrigo, R., Koschny, D., Rickman, H., Barucci, M.A., Bertaux, J.L., Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Güttler, C., Ip, W.-H., Kramm, J.R., Küppers, M., Lara, L.M., Lazzarin, M., Lopez Moreno, J.J., Marzari, F., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., and Wenzel, K.-P.

Published
2016
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14. Sublimation in bright spots on (1) Ceres

Author

Nathues, A., Hoffmann, M., Schaefer, M., Le Corre, L., Reddy, V., Platz, T., Cloutis, E.A., Christensen, U., Kneissl, T., Li, J.-Y., Mengel, K., Schmedemann, N., Schaefer, T., Russell, C.T., Applin, D.M., Buczkowski, D.L., Izawa, M.R.M., Keller, H.U., O'Brien, D.P., Pieters, C.M., Raymond, C.A., Ripken, J., Schenk, P.M., Schmidt, B.E., Sierks, H., Sykes, M.V., Thangjam, G.S., and Vincent, J.-B.

Subjects
Observations, Ceres (Dwarf planet) -- Observations, Ceres (Asteroid) -- Observations
Abstract

We observed Ceres using the Framing Camera (FC) on board the Dawn spacecraft. The FC is equipped with a panchromatic (clear) filter and seven colour filters, covering the wavelength range [...], The dwarf planet (1) Ceres, the largest object in the main asteroid belt (1) with a mean diameter of about 950 kilometres, is located at a mean distance from the Sun of about 2.8 astronomical units (one astronomical unit is the Earth-Sun distance). Thermal evolution models suggest that it is a differentiated body with potential geological activity (2,3). Unlike on the icy satellites of Jupiter and Saturn, where tidal forces are responsible for spewing briny water into space, no tidal forces are acting on Ceres. In the absence of such forces, most objects in the main asteroid belt are expected to be geologically inert. The recent discovery (4) of water vapour absorption near Ceres and previous detection of bound water and OH near and on Ceres (refs 5-7) have raised interest in the possible presence of surface ice. Here we report the presence of localized bright areas on Ceres from an orbiting imager (8). These unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material, although other compositions are possible. Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles (9,10) may explain this haze. We conclude that Ceres must have accreted material from beyond the 'snow line' (11), which is the distance from the Sun at which water molecules condense.

Published
2015

16. The geomorphology of (21) Lutetia: Results from the OSIRIS imaging system onboard ESA's Rosetta spacecraft

Author

Thomas, N., Barbieri, C., Keller, H.U., Lamy, P., Rickman, H., Rodrigo, R., Sierks, H., Wenzel, K.P., Cremonese, G., Jorda, L., Küppers, M., Marchi, S., Marzari, F., Massironi, M., Preusker, F., Scholten, F., Stephan, K., Barucci, M.A., Besse, S., El-Maarry, M.R., Fornasier, S., Groussin, O., Hviid, S.F., Koschny, D., Kührt, E., Martellato, E., Moissl, R., Snodgrass, C., Tubiana, C., and Vincent, J.-B.

Published
2012
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27. Morphology and dynamics of the upper cloud layer of Venus

Author

Markiewicz, W.J., Titov, D.V., Limaye, S.S., Keller, H.U., Ignatiev, N., Jaumann, R., Thomas, N., Michalik, H., Moissl, R., and Russo, P.

Subjects
Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Venus is completely covered by a thick cloud layer, of which the upper part is composed of sulphuric acid and some unknown aerosols (1). The cloud tops are in fast [...]

Published
2007

28. Properties of the dust cloud caused by the Deep Impact experiment

Author

Jorda, L., Lamy, P., Faury, G., Keller, H.U., Hviid, S., Kuppers, M., Koschny, D., Lecacheux, J., Gutierrez, P., and Lara, L.M.

Subjects
Image processing -- Analysis, Air pollution -- Analysis, Real estate industry -- Analysis, Astronomy, Earth sciences
Abstract

Byline: L. Jorda (a), P. Lamy (a), G. Faury (a), H.U. Keller (b), S. Hviid (b), M. Kuppers (b), D. Koschny (c), J. Lecacheux (d), P. Gutierrez (e), L.M. Lara (e) Keywords: Comets; Comets; dust; Comet Tempel-1; Comets, composition; Image processing Abstract: We present an analysis of the observations of the Deep Impact event performed by the OSIRIS narrow angle camera aboard the Rosetta spacecraft over two weeks, in an effort to characterize the cometary dust grains ejected from the nucleus of Comet 9P/Tempel 1. We adopt a Monte Carlo approach to generate calibrated synthetic images, and a linear combination of them is fitted to the calibrated images so as to determine the physical parameters of the dust cloud. Our model considers spherical olivine particles with a density of 3780 kgam.sup.-3. It incorporates constraints on the direction of the cone of emission coming from additional images obtained at Pic du Midi observatory, and constraints on the dust terminal velocities coming from the physics of the impact. We find that the slope of the differential dust size distribution of grains with radii Author Affiliation: (a) Laboratoire d'Astrophysique de Marseille, BP 8, 13376 Marseille Cedex 12, France (b) Max-Planck Institut fur Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany (c) Research and Scientific Support Department, ESTEC, 2200 AG Noordwijk, The Netherlands (d) Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon, France (e) Instituto de Astrofisica de Andalucia, CSIC, 18080 Granada, Spain Article History: Received 31 March 2006; Revised 19 September 2006

Published
2007

29. Exploring the asteroid belt with ion propulsion: Dawn mission history, status and plans

Author

Russell, C.T., Barucci, M.A., Binzel, R.P., Capria, M.T., Christensen, U., Coradini, A., De Sanctis, M.C., Feldman, W.C., Jaumann, R., Keller, H.U., Konopliv, A.S., McCord, T.B., McFadden, L.A., McKeegan, K.D., McSween, H.Y., Mottola, S., Nathues, A., Neukum, G., Pieters, C.M., Prettyman, T.H., Raymond, C.A., Sierks, H., Smith, D.E., Spohn, T., Sykes, M.V., Vilas, F., and Zuber, M.T.

Published
2007
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31. Venus Monitoring Camera for Venus Express

Author

Markiewicz, W.J., Titov, D.V., Ignatiev, N., Keller, H.U., Crisp, D., Limaye, S.S., Jaumann, R., Moissl, R., Thomas, N., Esposito, L., Watanabe, S., Fiethe, B., Behnke, T., Szemerey, I., Michalik, H., Perplies, H., Wedemeier, M., Sebastian, I., Boogaerts, W., Hviid, S.F., Dierker, C., Osterloh, B., Böker, W., Koch, M., Michaelis, H., Belyaev, D., Dannenberg, A., Tschimmel, M., Russo, P., Roatsch, T., and Matz, K.D.

Published
2007
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32. Dawn Discovery mission to Vesta and Ceres: Present status

Author

Russell, C.T., Capaccioni, F., Coradini, A., Christensen, U., De Sanctis, M.C., Feldman, W.C., Jaumann, R., Keller, H.U., Konopliv, A., McCord, T.B., McFadden, L.A., McSween, H.Y., Mottola, S., Neukum, G., Pieters, C.M., Prettyman, T.H., Raymond, C.A., Smith, D.E., Sykes, M.V., Williams, B., and Zuber, M.T.

Published
2006
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33. SMART-1 mission to the Moon: Status, first results and goals

Author

Foing, B.H., Racca, G.D., Marini, A., Evrard, E., Stagnaro, L., Almeida, M., Koschny, D., Frew, D., Zender, J., Heather, J., Grande, M., Huovelin, J., Keller, H.U., Nathues, A., Josset, J.L., Malkki, A., Schmidt, W., Noci, G., Birkl, R., Iess, L., Sodnik, Z., and McManamon, P.

Published
2006
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36. Infrared spectroscopy of comets with ISO: what we learned on the composition of cometary dust

Author

Crovisier, J., primary, Brooke, T.Y., additional, Leech, K., additional, Bockelée-Morvan, D., additional, Lellouch, E., additional, Hanner, M.S., additional, Altieri, B., additional, Keller, H.U., additional, Lim, T., additional, Encrenaz, T., additional, Salama, A., additional, Griffin, M., additional, de Graauw, T., additional, Van Dishoeck, E., additional, and Knacke, R.F., additional

Published
2002
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37. Results from the Mars Pathfinder camera

Author

Smith, P.H., Bell, III, J.F., Bridges, N.T., Britt, D.T., Gaddis, L., Greeley, R., Keller, H.U., Herkenhoff, K.E., Jaumann, R., Johnson, J.R., Kirk, R.L., Lemmon, M., Maki, J.N., Malin, M.C., Murchie, S.L., Oberst, J., Parker, T.J., Reid, R.J., Sablotny, R., Soderblom, L.A., Stoker, C., Sullivan, R., Thomas, N., Tomasko, M.G., Ward, W., and Wegryn, E.

Subjects
Mars Pathfinder (Space probe) -- Observations, Planets -- Portrayals, Mars probes -- Observations, Mars (Planet) -- Portrayals, Science and technology
Abstract

Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified [...]

Published
1997

38. Time evolution of dust deposits in the Hapi region of comet 67P/Churyumov-Gerasimenko

Author

German Centre for Air and Space Travel, Centre National de la Recherche Scientifique (France), Agenzia Spaziale Italiana, Ministerio de Ciencia, Innovación y Universidades (España), Government of Sweden, Cambianica, P., Fulle, M., Cremonese, G., Simioni, E., Naletto, G., Massironi, M., Penasa, L., Lucchetti, A., Pajola, M., Bertini, I., Bodewits, D., Ceccarelli, C., Ferri, F., Fornasier, S., Frattin, E., Güttler, C., Gutiérrez, Pedro J., Keller, H.U., Kührt, E., Küppers, M., La Forgia, F., Lazzarin, M., Marzari, F., Mottola, S., Sierks, H., Toth, I., Tubiana, C., Vincent, J.B., German Centre for Air and Space Travel, Centre National de la Recherche Scientifique (France), Agenzia Spaziale Italiana, Ministerio de Ciencia, Innovación y Universidades (España), Government of Sweden, Cambianica, P., Fulle, M., Cremonese, G., Simioni, E., Naletto, G., Massironi, M., Penasa, L., Lucchetti, A., Pajola, M., Bertini, I., Bodewits, D., Ceccarelli, C., Ferri, F., Fornasier, S., Frattin, E., Güttler, C., Gutiérrez, Pedro J., Keller, H.U., Kührt, E., Küppers, M., La Forgia, F., Lazzarin, M., Marzari, F., Mottola, S., Sierks, H., Toth, I., Tubiana, C., and Vincent, J.B.

Abstract

Aims. We provide a measurement of the seasonal evolution of the dust deposit erosion and accretion in the Hapi region of comet 67P/Churyumov-Gerasimenko with a vertical accuracy of 0.2-0.9 m. Methods. We used OSIRIS Narrow Angle Camera images with a spatial scale of lower than 1.30 m px-1 and developed a tool to monitor the time evolution of 22 boulder heights with respect to the surrounding dust deposit. The tool is based on the measurement of the shadow length projected by the boulder on the surrounding pebble deposit. Assuming the position of the boulders does not change during the observational period, boulder height variations provide an indication of how the thickness of the surrounding dust layer varies over time through erosion and accretion phenomena. Results. We measured an erosion of the dust deposit of 1.7 ± 0.2 m during the inbound orbit until 12 December, 2014. This value nearly balances the fallout from the southern hemisphere during perihelion cometary activity. During the perihelion phase, the dust deposit then increased by 1.4 ± 0.8 m. This is interpreted as a direct measurement of the fallout thickness. By comparing the erosion rate and dust volume loss rate at the Hapi region measured in the coma, the fallout represents ~96% in volume of the ejecta. The amount of the eroded pristine material from the southern hemisphere, together with its subsequent transport and fallout on the nucleus, led us to discuss the pristine water ice abundance in comet 67P. We determine that the refractory-to-ice mass ratio ranges from 6 to 110 in the perihelion-eroded pristine nucleus, providing a pristine ice mass fraction of (8 ± 7)% in mass. © 2020 ESO.

Published
2020

39. Dawn: A journey in space and time

Author

Russell, C.T., Coradini, A., Christensen, U., De Sanctis, M.C., Feldman, W.C., Jaumann, R., Keller, H.U., Konopliv, A.S., McCord, T.B., McFadden, L.A., McSween, H.Y., Mottola, S., Neukum, G., Pieters, C.M., Prettyman, T.H., Raymond, C.A., Smith, D.E., Sykes, M.V., Williams, B.G., Wise, J., and Zuber, M.T.

Published
2004
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40. Observations of Comet P/Faye 1991 XXI with the planetary camera of the Hubble Space Telescope

Author

Lamy, P.L., Toth, I., Grun, E., Keller, H.U., Sekanina, Z., and West, R.M.

Subjects
Hubble Space Telescope (Artificial satellite) -- Research, Comets -- Observations, Astronomy, Earth sciences
Abstract

Comet P/Faye 1991 XXI (1991 n) was observed with the planetary camera (PC) of the Hubble Space Telescope (HST) between October 29 and November 21, 1991, when its geocentric distance was in the range 0.62-0.67 AU. The resulting high resolution - a single PC pixel projected to a distance of [appoximately]20 km at the comet - made it possible to clearly discriminate the nucleus and to study the dust coma within [approximately]100 km from the nucleus. The spherical aberration which affected the early operation of the HST has severely complicated the analysis and image restoration using the Richardson-Lucy method has failed to give satisfactory results. The coma is dominated by the point spread function (PSF) of the nucleus up to a radial distance of [approximately]100 km and cannot be recovered. Beyond, it is affected by the spherical aberration up to approximately 750 km and was analyzed by comparison with a grid of models convolved with appropriate PSFs. Beyond 750 km, it remains unaffected and can be studied directly. From the outer to the innermost regions, the coma presents an elongated shape which may be explained either by an active source on the nucleus or, more likely, by a projection effect of the dust tail. If this second interpretation is correct, then the temporal evolution of the comet is very slow and smooth, suggesting an extended source of dust on the nucleus. The dust production rate, corrected for the projection effect of the tail, amounts to 125 kg [sec.sup.-1].

Published
1996

44. The microscope for Beagle 2

Author

Thomas, N., Lüthi, B.S., Hviid, S.F., Keller, H.U., Markiewicz, W.J., Blümchen, T., Basilevsky, A.T., Smith, P.H., Tanner, R., Oquest, C., Reynolds, R., Josset, J.-L., Beauvivre, S., Hofmann, B., Rüffer, P., and Pillinger, C.T.

Published
2004
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45. On the stability of dust particle orbits around cometary nuclei

Author

Richter, K. and Keller, H.U.

Subjects
Comets -- Research, Geometrical models -- Usage, Astronomy, Earth sciences
Abstract

Solar radiation pressure force affects the orbital evolution of the dust particles, extending to distances of up to 10 m from cometary nucleus. Tidal force dominates the decreasing radiation pressure in the case of very large particles. Additional perturbations, very common in comets, are caused by rotation of nonspherical nucleus and gas dynamical acceleration processes. A geometrical model is used to explain the dust particle orbit evolution.

Published
1995

46. The formation of cometary surface crusts

Author

Kuhrt, E. and Keller, H.U.

Subjects
Comets -- Observations, Astronomy, Earth sciences
Abstract

A model that includes cohesive forces within the refractory material of cometary nuclei describes the inactivity of nuclear surfaces. Numerical calculation explains cometary surface crusts, their activity and vapor pressure under the crusts. Cohesion of matrix material reveals a higher strength than vapor pressure under the crust. Different dust-to-ice ratios in cometary nuclei structures and physical parameters explain restricted and persistent activities of comets.

Published
1994

47. Interpretation of the KRFM-infrared measurements of Phobos

Author

Kuhrt, E., Giese, B., Keller, H.U., and Ksanfomality, L.V.

Subjects
Infrared radiation -- Research, Phobos (Satellite) -- Research, Radio astronomy -- Research, Extraterrestrial radiation -- Research, Astronomy, Earth sciences
Abstract

Data from the radiometric measurements of Phobos was used to form a thermal model which would analyze the outermost layer of regolith. Data took into consideration the roughness of the surface and the ellipsoidal shape of the satellite. It was found that the measured thermal flux was determined by heat conductivity and roughness of the surface and the coarser regolith of Phobos may be explained by the impact velocity and fractionation process of the radio waves.

Published
1992

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