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An orbital water-ice cycle on comet 67P from colour changes
Gianrico Filacchione1, Fabrizio Capaccioni2, Mauro Ciarniello2
1INAF-IAPS, Institute for Space Astrophysics and Planetology, Rome, Italy. gianrico.filacchione@inaf.it.
Nature
|February 7, 2020
Summary
Comet 67P/Churyumov-Gerasimenko exhibits opposite seasonal color changes on its surface and in its coma. Organic-rich dust reddens the coma, while exposed ice blues the nucleus surface during perihelion passage.
Area of Science:
- Planetary Science
- Cometary Science
- Astrochemistry
Background:
- Cometary activity is driven by solar heating, leading to gaseous release and dust ejection.
- Cometary coma and nucleus properties evolve dynamically throughout an orbit.
- Dust particle color varies with composition (organic, silicate, water ice) and grain size.
Purpose of the Study:
- To observe and analyze seasonal color cycles on comet 67P/Churyumov-Gerasimenko's surface and coma.
- To investigate the relationship between solar heating, dust composition, and observed color changes.
Main Methods:
- Spectral analysis of observations of comet 67P/Churyumov-Gerasimenko.
- Monitoring color variations in the coma and on the nucleus surface through perihelion passage.
Main Results:
- Observed two opposite seasonal color cycles in the coma and on the nucleus.
- Coma reddening attributed to enrichment of sub-micrometre organic material and amorphous carbon grains.
- Nucleus surface showed bluer hues due to exposure of pristine icy layers as dust was removed.
Conclusions:
- Cometary dust composition and grain size significantly influence coma color.
- Seasonal changes reveal a dynamic interplay between dust removal, ice sublimation, and surface evolution.
- Far from the Sun, surface dehydration and dust redeposition reduce water ice abundance and coma redness.
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