@article{CiarnielloFulleRaponietal.2022,
  author    = {Ciarniello, Mauro and Fulle, Marco and Raponi, Andrea and Filacchione, Gianrico and Capaccioni, Fabrizio and Rotundi, Alessandra and Rinaldi, Giovanna and Formisano, Michelangelo and Magni, Gianfranco and Tosi, Federico and De Sanctis, Maria Cristina and Capria, Maria Teresa and Longobardo, Andrea and Beck, Pierre and Fornasier, Sonia and Kappel, David and Mennella, Vito and Mottola, Stefano and Rousseau, Batiste and Arnold, Gabriele},
  title     = {Macro and micro structures of pebble-made cometary nuclei reconciled by seasonal evolution},
  series = {Nature astronomy},
  volume    = {6},
  journal   = {Nature astronomy},
  number    = {5},
  publisher = {Nature Research},
  address   = {Berlin},
  issn      = {2397-3366},
  doi       = {10.1038/s41550-022-01625-y},
  pages     = {546 -- 553},
  year      = {2022},
  abstract  = {Comets evolve due to sublimation of ices embedded inside porous dust, triggering dust emission (that is, erosion) followed by mass loss, mass redistribution and surface modifications. Surface changes were revealed by the Deep Impact and Stardust NExT missions for comet 9P/Tempel 1 (ref.(1)), and a full inventory of the processes modifying cometary nuclei was provided by Rosetta while it escorted comet 67P/Churyumov-Gerasimenko for approximately two years(2-4). Such observations also showed puzzling water-ice-rich spots that stood out as patches optically brighter and spectrally bluer than the average cometary surfaces(5-9). These are up to tens of metres large and indicate macroscopic compositional dishomogeneities apparently in contrast with the structural homogeneity above centimetre scales of pebble-made nuclei(10). Here we show that the occurrence of blue patches determines the seasonal variability of the nucleus colour(4,11,12) and gives insight into the internal structure of comets. We define a new model that links the centimetre-sized pebbles composing the nucleus(10) and driving cometary activity(13,14) to metre-sized water-ice-enriched blocks embedded in a drier matrix. The emergence of blue patches is due to the matrix erosion driven by CO2-ice sublimation that exposes the water-ice-enriched blocks, which in turn are eroded by water-ice sublimation when exposed to sunlight. Our model explains the observed seasonal evolution of the nucleus and reconciles the available data at micro (sub-centimetre) and macro (metre) scales.},
  language  = {en}
}