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8. The concept of a facility for cosmic dust research on the International Space Station

Author

Blum, Juergen, Cabane, Michel, Fonda, Mark, Giovane, Frank, Gustafson, Bo A. S, Keller, Horst U, Markiewicz, Wojciech J, Levasseur-Regourd, Any-Chantal, Worms, Jean-Claude, Nuth, Joseph A, and Rogers, Fred

Subjects
Spacecraft Instrumentation
Abstract

A proposal for the development of a permanently operating facility for the experimental investigation of cosmic dust-related phenomena onboard the International Space Station (ISS) is presented. Potential applications for this facility are the convection-free nucleation of dust grains, studies of coagulation and aggregation phenomena in a microgravity environment, investigations of heat transport through, and dust emissions from, high-porosity cometary analogs, and experiments on the interaction of very fluffy dust grains with electromagnetic radiation and with low pressure gas flows. Possible extensions of such a facility are towards aerosol science and colloidal plasma research.

Published
1996

9. The southern hemisphere of 67P/Churyumov-Gerasimenko : Analysis of the preperihelion size-frequency distribution of boulders >= 7m

Author

Pajola, Maurizio, Lucchetti, Alice, Vincent, Jean-Baptiste, Oklay, Nilda, El-Maarry, Mohamed R., Bertini, Ivano, Naletto, Giampiero, Lazzarin, Monica, Massironi, Matteo, Sierks, Holger, Barbieri, Cesare, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Boudreault, Steve, Cremonese, Gabriele, Da Deppo, Vania, Davidsson, Bjorn, Debei, Stefano, De Cecco, Mariolino, Deller, Jakob, Fornasier, Sonia, Fulle, Marco, Gicquel, Adeline, Groussin, Olivier, Gutierrez, Pedro J., Guetler, Carsten, Hofmann, Marc, Hoefner, Sebastian, Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kuehrt, Ekkehard, Kuppers, Michael, La Forgia, Fiorangela, Lara, Luisa M., Lee, Jui-Chi, Lin, Zhong-Yi, Lopez Moreno, Jose J., Marzari, Francesco, Michalik, Harald, Mottola, Stefano, Preusker, Frank, Scholten, Frank, Thomas, Nicholas, Toth, Imre, Tubiana, Cecilia, Pajola, Maurizio, Lucchetti, Alice, Vincent, Jean-Baptiste, Oklay, Nilda, El-Maarry, Mohamed R., Bertini, Ivano, Naletto, Giampiero, Lazzarin, Monica, Massironi, Matteo, Sierks, Holger, Barbieri, Cesare, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Boudreault, Steve, Cremonese, Gabriele, Da Deppo, Vania, Davidsson, Bjorn, Debei, Stefano, De Cecco, Mariolino, Deller, Jakob, Fornasier, Sonia, Fulle, Marco, Gicquel, Adeline, Groussin, Olivier, Gutierrez, Pedro J., Guetler, Carsten, Hofmann, Marc, Hoefner, Sebastian, Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kuehrt, Ekkehard, Kuppers, Michael, La Forgia, Fiorangela, Lara, Luisa M., Lee, Jui-Chi, Lin, Zhong-Yi, Lopez Moreno, Jose J., Marzari, Francesco, Michalik, Harald, Mottola, Stefano, Preusker, Frank, Scholten, Frank, Thomas, Nicholas, Toth, Imre, and Tubiana, Cecilia

Abstract

Aims. We calculate the size-frequency distribution of the boulders on the southern hemisphere of comet 67P Churyumov-Gerasimenko (67P), which was in shadow before the end of April 2015. We compare the new results with those derived from the northern hemisphere and equatorial regions of 67P, highlighting the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 2 May 2015 at a distance of 125 km from the nucleus. The scale of this dataset is 2.3 m/px; the high resolution of the images, coupled with the favorable observation phase angle of 62 degrees, provided the possibility to unambiguously identify boulders >= 7 m on the surface of 67P and to manually extract them with the software ArcGIS. We derived the size-frequency distribution of the illuminated southern hemisphere. Results. We found a power-law index of -3.6 +/- 0.2 for the boulders on the southern hemisphere with a diameter range of 7-35 m. The power-law index is equal to the one previously found on northern and equatorial regions of 67P, suggesting that similar boulder formation processes occur in both hemispheres. The power-law index is related to gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. In addition, the presence of a larger number of boulders per km(2) in the southern hemisphere, which is a factor of 3 higher with respect to the northern hemisphere, suggests that the southernmost terrains of 67P are affected by a stronger thermal fracturing and sublimating activity, hence possibly causing larger regressive erosion and gravitational events.

Published
2016
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10. Aswan site on comet 67P/Churyumov-Gerasimenko : Morphology, boulder evolution, and spectrophotometry

Author

Pajola, Maurizio, Oklay, Nilda, La Forgia, Fiorangela, Giacomini, Lorenza, Massironi, Matteo, Bertini, Ivano, El-Maarry, M. R., Marzari, Francesco, Preusker, Frank, Scholten, Frank, Hoefner, Sebastian, Lee, Jui-Chi, Vincent, Jean-Baptiste, Groussin, Olivier, Naletto, Giampiero, Lazzarin, Monica, Barbieri, Cesare, Sierks, Holger, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Cremonese, Gabriele, Da Deppoll, Vania, Davidsson, Bjoern, De Cecco, Mariolino, Debei, Stefano, Ferri, Francesca, Fornasier, Sonia, Fulle, Marco, Guettler, Carsten, Gutierrez, Pedro J., Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kueppers, Michael, Kuert, Ekkehard, Lara, Luisa M., Lin, Zhong-Yi, Moreno, Jose J. Lopez, Magrin, Sara, Michalik, Harald, Mottola, Stefano, Thomas, Nicholas, Tubiana, Cecilia, Pajola, Maurizio, Oklay, Nilda, La Forgia, Fiorangela, Giacomini, Lorenza, Massironi, Matteo, Bertini, Ivano, El-Maarry, M. R., Marzari, Francesco, Preusker, Frank, Scholten, Frank, Hoefner, Sebastian, Lee, Jui-Chi, Vincent, Jean-Baptiste, Groussin, Olivier, Naletto, Giampiero, Lazzarin, Monica, Barbieri, Cesare, Sierks, Holger, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Cremonese, Gabriele, Da Deppoll, Vania, Davidsson, Bjoern, De Cecco, Mariolino, Debei, Stefano, Ferri, Francesca, Fornasier, Sonia, Fulle, Marco, Guettler, Carsten, Gutierrez, Pedro J., Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kueppers, Michael, Kuert, Ekkehard, Lara, Luisa M., Lin, Zhong-Yi, Moreno, Jose J. Lopez, Magrin, Sara, Michalik, Harald, Mottola, Stefano, Thomas, Nicholas, and Tubiana, Cecilia

Abstract

Aims. We provide a detailed morphological analysis of the Aswan site on comet 67P/Churyumov-Gerasimenko (67P). We derive the size-frequency distribution of boulders >= 2 m and correlate this distribution with the gravitational slopes for the first time on a comet. We perform the spectral analysis of this region to understand if possible surface variegation is related to the different surface textures observable on the different units. Methods. We used two OSIRIS Narrow Angle Camera (NAC) image data sets acquired on September 19 and 22, 2014, with a scale of 0.5 m/px. Gravitational slopes derived from the 3D shape model of 67P were used to identify and interpret the different units of the site. By means of the high-resolution NAC data sets, boulders >= 2.0 m can be unambiguously identified and extracted using the software ArcGIS. Coregistered and photometrically corrected color cubes were used to perform the spectral analyses, and we retrieved the spectral properties of the Aswan units. Results. The high-resolution morphological map of the Aswan site (0.68 km(2)) shows that this site is characterized by four different units: fine-particle deposits located on layered terrains, gravitational accumulation deposits, taluses, and the outcropping layered terrain. Multiple lineaments are identified on the Aswan cliff, such as fractures, exposed layered outcrops, niches, and terraces. Close to the terrace margin, several arched features observed in plan view suggest that the margin progressively retreats as a result of erosion. The size-frequency of boulders >= 2 m in the entire study area has a power-law index of -3.9 +0.2/-0.3 (1499 boulders >= 2 m/km(2)), suggesting that the Aswan site is mainly dominated by gravitational events triggered by sublimation and/or thermal insolation weathering causing regressive erosion. The boulder size-frequency distribution versus gravitational slopes indicates that when higher gravitational slope terrains are considered, only

Published
2016
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11. Aswan site on comet 67P/Churyumov-Gerasimenko: Morphology, boulder evolution, and spectrophotometry

Author

Pajola, Maurizio, primary, Oklay, Nilda, additional, La Forgia, Fiorangela, additional, Giacomini, Lorenza, additional, Massironi, Matteo, additional, Bertini, Ivano, additional, El-Maarry, M. R., additional, Marzari, Francesco, additional, Preusker, Frank, additional, Scholten, Frank, additional, Höfner, Sebastian, additional, Lee, Jui-Chi, additional, Vincent, Jean-Baptiste, additional, Groussin, Olivier, additional, Naletto, Giampiero, additional, Lazzarin, Monica, additional, Barbieri, Cesare, additional, Sierks, Holger, additional, Lamy, Philippe, additional, Rodrigo, Rafael, additional, Koschny, Detlef, additional, Rickman, Hans, additional, Keller, Horst U., additional, Agarwal, Jessica, additional, A’Hearn, Michael F., additional, Barucci, Maria A., additional, Bertaux, Jean-Loup, additional, Cremonese, Gabriele, additional, Deppo, Vania Da, additional, Davidsson, Björn, additional, De Cecco, Mariolino, additional, Debei, Stefano, additional, Ferri, Francesca, additional, Fornasier, Sonia, additional, Fulle, Marco, additional, Güttler, Carsten, additional, Gutierrez, Pedro J., additional, Hviid, Stubbe F., additional, Ip, Wing-Huen, additional, Jorda, Laurent, additional, Knollenberg, Jörg, additional, Kramm, J.-Rainer, additional, Küppers, Michael, additional, Kürt, Ekkehard, additional, Lara, Luisa M., additional, Lin, Zhong-Yi, additional, Lopez Moreno, Jose J., additional, Magrin, Sara, additional, Michalik, Harald, additional, Mottola, Stefano, additional, Thomas, Nicholas, additional, and Tubiana, Cecilia, additional

Published
2016
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12. The southern hemisphere of 67P/Churyumov-Gerasimenko: Analysis of the preperihelion size-frequency distribution of boulders ≥7 m

Author

Pajola, Maurizio, primary, Lucchetti, Alice, additional, Vincent, Jean-Baptiste, additional, Oklay, Nilda, additional, El-Maarry, Mohamed R., additional, Bertini, Ivano, additional, Naletto, Giampiero, additional, Lazzarin, Monica, additional, Massironi, Matteo, additional, Sierks, Holger, additional, Barbieri, Cesare, additional, Lamy, Philippe, additional, Rodrigo, Rafael, additional, Koschny, Detlef, additional, Rickman, Hans, additional, Keller, Horst U., additional, Agarwal, Jessica, additional, A’Hearn, Michael F., additional, Barucci, Maria A., additional, Bertaux, Jean-Loup, additional, Boudreault, Steve, additional, Cremonese, Gabriele, additional, Deppo, Vania Da, additional, Davidsson, Björn, additional, Debei, Stefano, additional, De Cecco, Mariolino, additional, Deller, Jakob, additional, Fornasier, Sonia, additional, Fulle, Marco, additional, Gicquel, Adeline, additional, Groussin, Olivier, additional, Gutierrez, Pedro J., additional, Güttler, Carsten, additional, Hofmann, Marc, additional, Höfner, Sebastian, additional, Hviid, Stubbe F., additional, Ip, Wing-Huen, additional, Jorda, Laurent, additional, Knollenberg, Jörg, additional, Kramm, J.-Rainer, additional, Kührt, Ekkehard, additional, Küppers, Michael, additional, La Forgia, Fiorangela, additional, Lara, Luisa M., additional, Lee, Jui-Chi, additional, Lin, Zhong-Yi, additional, Lopez Moreno, Jose J., additional, Marzari, Francesco, additional, Michalik, Harald, additional, Mottola, Stefano, additional, Preusker, Frank, additional, Scholten, Frank, additional, Thomas, Nicholas, additional, Toth, Imre, additional, and Tubiana, Cecilia, additional

Published
2016
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13. Size-frequency distribution of boulders >= 7 m on comet 67P/Churyumov-Gerasimenko

Author

Pajola, Maurizio, Vincent, Jean-Baptiste, Guettler, Carsten, Lee, Jui-Chi, Bertini, Ivano, Massironi, Matteo, Simioni, Emanuele, Marzari, Francesco, Giacomini, Lorenza, Lucchetti, Alice, Barbieri, Cesare, Cremonese, Gabriele, Naletto, Giampiero, Pommerol, Antoine, El-Maarry, Mohamed R., Besse, Sebastien, Kueppers, Michael, La Forgia, Fiorangela, Lazzarin, Monica, Thomas, Nicholas, Auger, Anne-Therese, Sierks, Holger, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Da Deppo, Vania, Davidsson, Björn, De Cecco, Mariolino, Debei, Stefano, Ferri, Francesca, Fornasier, Sonia, Fulle, Marco, Groussin, Olivier, Gutierrez, Pedro J., Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kuert, Ekkehard, Lara, Luisa M., Lin, Zhong-Yi, Lopez Moreno, Jose J., Magrin, Sara, Marchi, Simone, Michalik, Harald, Moissl, Richard, Mottola, Stefano, Oklay, Nilda, Preusker, Frank, Scholten, Frank, Tubiana, Cecilia, Pajola, Maurizio, Vincent, Jean-Baptiste, Guettler, Carsten, Lee, Jui-Chi, Bertini, Ivano, Massironi, Matteo, Simioni, Emanuele, Marzari, Francesco, Giacomini, Lorenza, Lucchetti, Alice, Barbieri, Cesare, Cremonese, Gabriele, Naletto, Giampiero, Pommerol, Antoine, El-Maarry, Mohamed R., Besse, Sebastien, Kueppers, Michael, La Forgia, Fiorangela, Lazzarin, Monica, Thomas, Nicholas, Auger, Anne-Therese, Sierks, Holger, Lamy, Philippe, Rodrigo, Rafael, Koschny, Detlef, Rickman, Hans, Keller, Horst U., Agarwal, Jessica, A'Hearn, Michael F., Barucci, Maria A., Bertaux, Jean-Loup, Da Deppo, Vania, Davidsson, Björn, De Cecco, Mariolino, Debei, Stefano, Ferri, Francesca, Fornasier, Sonia, Fulle, Marco, Groussin, Olivier, Gutierrez, Pedro J., Hviid, Stubbe F., Ip, Wing-Huen, Jorda, Laurent, Knollenberg, Joerg, Kramm, J. -Rainer, Kuert, Ekkehard, Lara, Luisa M., Lin, Zhong-Yi, Lopez Moreno, Jose J., Magrin, Sara, Marchi, Simone, Michalik, Harald, Moissl, Richard, Mottola, Stefano, Oklay, Nilda, Preusker, Frank, Scholten, Frank, and Tubiana, Cecilia

Abstract

Aims. We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera, NAC. on 5 and 6 August 2014. The scale of these images (2.44-2.03 m/px) is such that boulders >= 7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowine of the surface (observation phase angle ranging from 48 to 53), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. Results. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km(2)), with a global number density of nearly 100/km(2) and a cumulative size-frequency distribution represented by a power-law with index of -3.6 +0.2/-0.3. The two lobes of 67P appear to have slightly different distributions, with an index of -3.5 +0.2/-0.3 for the main lobe (body) and -4.0 +0.31-0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of -2.2 +0.2/-0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km(2) of loca

Published
2015
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14. Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko

Author

Pajola, Maurizio, primary, Vincent, Jean-Baptiste, additional, Güttler, Carsten, additional, Lee, Jui-Chi, additional, Bertini, Ivano, additional, Massironi, Matteo, additional, Simioni, Emanuele, additional, Marzari, Francesco, additional, Giacomini, Lorenza, additional, Lucchetti, Alice, additional, Barbieri, Cesare, additional, Cremonese, Gabriele, additional, Naletto, Giampiero, additional, Pommerol, Antoine, additional, El-Maarry, Mohamed R., additional, Besse, Sébastien, additional, Küppers, Michael, additional, La Forgia, Fiorangela, additional, Lazzarin, Monica, additional, Thomas, Nicholas, additional, Auger, Anne-Thérèse, additional, Sierks, Holger, additional, Lamy, Philippe, additional, Rodrigo, Rafael, additional, Koschny, Detlef, additional, Rickman, Hans, additional, Keller, Horst U., additional, Agarwal, Jessica, additional, A’Hearn, Michael F., additional, Barucci, Maria A., additional, Bertaux, Jean-Loup, additional, Deppo, Vania Da, additional, Davidsson, Björn, additional, De Cecco, Mariolino, additional, Debei, Stefano, additional, Ferri, Francesca, additional, Fornasier, Sonia, additional, Fulle, Marco, additional, Groussin, Olivier, additional, Gutierrez, Pedro J., additional, Hviid, Stubbe F., additional, Ip, Wing-Huen, additional, Jorda, Laurent, additional, Knollenberg, Jörg, additional, Kramm, J.-Rainer, additional, Kürt, Ekkehard, additional, Lara, Luisa M., additional, Lin, Zhong-Yi, additional, Moreno, Jose J. Lopez, additional, Magrin, Sara, additional, Marchi, Simone, additional, Michalik, Harald, additional, Moissl, Richard, additional, Mottola, Stefano, additional, Oklay, Nilda, additional, Preusker, Frank, additional, Scholten, Frank, additional, and Tubiana, Cecilia, additional

Published
2015
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15. Beagle 2: a proposed exobiology lander for ESA's 2003 Mars Express mission

Author

Sims, Mark R., primary, Pillinger, C. T., additional, Wright, I. P., additional, Cole, Richard E., additional, Whitehead, S., additional, Wells, Alan A., additional, Wittmann, K., additional, Richter, L., additional, Kochan, H., additional, Hamacher, Hans, additional, Johnstone, Alan, additional, Rees, K., additional, Turner, R. F., additional, Peskett, S. C., additional, Brack, A., additional, Hobbs, J., additional, Berthoud, L., additional, Durrant, R., additional, Higgins, J., additional, Windsor, J., additional, Keller, Horst U., additional, Rosenbauer, H., additional, Thomas, Nicolas, additional, Lingard, J. S., additional, Underwood, J. C., additional, Neukum, Gerhard, additional, and Turner, R., additional

Published
1998
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16. Size-frequency distribution of boulders ≥7 m on comet 67P/Churyumov-Gerasimenko

Author

Da Deppo, Vania, Ip, Wing-Huen, Marzari, Francesco, Scholten, Frank, Preusker, Frank, Besse, Sebastien, Guettler, Carsten, Mottola, Stefano, Barucci, Maria A., Davidsson, Bjoern, De Cecco, Mariolino, Kuert, Ekkehard, La Forgia, Fiorangela, Lopez Moreno, Jose J., Fornasier, Sonia, Hviid, Stubbe F., Cremonese, Gabriele, Lee, Jui-Chi, Bertini, Ivano, Kueppers, Michael, Lazzarin, Monica, Gutierrez, Pedro J., Ferri, Francesca, Lamy, Philippe, Thomas, Nicholas, Lara, Luisa M., Massironi, Matteo, Koschny, Detlef, Auger, Anne-Therese, Vincent, Jean-Baptiste, Knollenberg, Joerg, Debei, Stefano, Groussin, Olivier, Fulle, Marco, Jorda, Laurent, Magrin, Sara, Oklay, Nilda, Bertaux, Jean-Loup, Sierks, Holger, Elmaarry, Mohamed Ramy, Kramm, J. Rainer, Barbieri, Cesare, Keller, Horst U., A'Hearn, Michael F., Pajola, Maurizio, Marchi, Simone, Simioni, Emanuele, Giacomini, Lorenza, Pommerol, Antoine, Tubiana, Cecilia, Lucchetti, Alice, Rickman, Hans, Naletto, Giampiero, Lin, Zhong-Yi, Agarwal, Jessica, Moissl, Richard, Rodrigo, Rafael, and Michalik, Harald

Subjects
13. Climate action, 530 Physics, 500 Science
Abstract

Aims. We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera, NAC, on 5 and 6 August 2014. The scale of these images (2.44−2.03 m/px) is such that boulders ≥7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowing of the surface (observation phase angle ranging from 48° to 53°), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. Results. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km2), with a global number density of nearly 100/km2 and a cumulative size-frequency distribution represented by a power-law with index of −3.6 +0.2/−0.3. The two lobes of 67P appear to have slightly different distributions, with an index of −3.5 +0.2/−0.3 for the main lobe (body) and −4.0 +0.3/−0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of −2.2 +0.2/−0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km2 of localized areas on 67P. By comparing the cumulative size-frequency distributions of similar geomorphological settings, we derived similar power-law index values. This suggests that despite the selected locations on different and often opposite sides of the comet, similar sublimation or activity processes, pit formation or collapses, as well as thermal stresses or fracturing events occurred on multiple areas of the comet, shaping its surface into the appearance we see today.

17. The southern hemisphere of 67P/Churyumov-Gerasimenko: Analysis of the preperihelion size-frequency distribution of boulders ≥7 m

Author

La Forgia, Fiorangela, Hofmann, Marc, Fulle, Marco, Keller, Horst U., Toth, Imre, Agarwal, Jessica, Groussin, Olivier, Lopez Moreno, Jose J., De Cecco, Mariolino, Michalik, Harald, Gutierrez, Pedro J., Höfner, Sebastian, Vincent, Jean-Baptiste, Gicquel, Adeline, Naletto, Giampiero, Fornasier, Sonia, Deppo, Vania Da, Rickman, Hans, Elmaarry, Mohamed Ramy, Koschny, Detlef, Massironi, Matteo, Barucci, Maria A., Thomas, Nicolas, Kramm, J.-Rainer, Scholten, Frank, Bertaux, Jean-Loup, Lara, Luisa M., Lin, Zhong-Yi, Kührt, Ekkehard, Bertini, Ivano, Lamy, Philippe, Mottola, Stefano, Sierks, Holger, Lazzarin, Monica, Lee, Jui-Chi, Oklay, Nilda, Jorda, Laurent, Hviid, Stubbe F., Cremonese, Gabriele, Marzari, Francesco, Debei, Stefano, Pajola, Maurizio, Lucchetti, Alice, Davidsson, Björn, Tubiana, Cecilia, Küppers, Michael, Preusker, Frank, Ip, Wing-Huen, Güttler, Carsten, Boudreault, Steve, Rodrigo, Rafael, Barbieri, Cesare, Knollenberg, Jörg, A’Hearn, Michael F., and Deller, Jakob

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

Aims. We calculate the size-frequency distribution of the boulders on the southern hemisphere of comet 67P Churyumov-Gerasimenko (67P), which was in shadow before the end of April 2015. We compare the new results with those derived from the northern hemisphere and equatorial regions of 67P, highlighting the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 2 May 2015 at a distance of 125 km from the nucleus. The scale of this dataset is 2.3 m/px; the high resolution of the images, coupled with the favorable observation phase angle of 62 degrees, provided the possibility to unambiguously identify boulders ≥ 7 m on the surface of 67P and to manually extract them with the software ArcGIS. We derived the size-frequency distribution of the illuminated southern hemisphere. Results. We found a power-law index of -3.6 + 0.2 for the boulders on the southern hemisphere with a diameter range of 7-35 m. The power-law index is equal to the one previously found on northern and equatorial regions of 67P, suggesting that similar boulder formation processes occur in both hemispheres. The power-law index is related to gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. In addition, the presence of a larger number of boulders per km² in the southern hemisphere, which is a factor of 3 higher with respect to the northern hemisphere, suggests that the southernmost terrains of 67P are affected by a stronger thermal fracturing and sublimating activity, hence possibly causing larger regressive erosion and gravitational events.

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