Data di Pubblicazione:
2020
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 mpx1 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.
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 mpx1 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.
Tipologia CRIS:
01.01 - Articolo in rivista
Keywords:
comets: general – comets: individual: 67P/Churyumov-Gerasimenko – methods: data analysis – methods: numerical
Elenco autori:
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, P. 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.
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