Dayside-to-nightside dust coma brightness asymmetry and its implications for nightside activity at Comet 67P/Churyumov–Gerasimenko
| Autor: | Nicolas Thomas, Jong-Shinn Wu, O. Pinzón-Rodríguez, Selina-Barbara Gerig, Raphael Marschall |
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| Rok vydání: | 2020 |
| Předmět: |
Physics
Brightness 010504 meteorology & atmospheric sciences Particle propagation media_common.quotation_subject Astronomy and Astrophysics Astrophysics Gas dynamics 01 natural sciences Asymmetry 13. Climate action Space and Planetary Science 0103 physical sciences Sublimation (phase transition) Outflow 010303 astronomy & astrophysics 0105 earth and related environmental sciences media_common Dust emission |
| Zdroj: | Icarus. 351:113968 |
| ISSN: | 0019-1035 |
| DOI: | 10.1016/j.icarus.2020.113968 |
| Popis: | We have determined the dust coma brightness ratio between the dayside and the nightside (DS:NS) in OSIRIS images of comet 67P/Churyumov–Gerasimenko and compared them to results from numerical dust coma simulations to learn more about the dynamic processes that are involved in coma formation. The primary focus of this paper lies in the analysis of a subset of OSIRIS images acquired during one comet rotation on 11. April 2015 when the spacecraft was at a phase angle of 90 ∘ and therefore directly above the terminator. The DS:NS ratio was found to be 2.49 ± 0.18 on average - a very low value if insolation-driven sublimation of water dominates dust emission. We investigated two possible hypotheses: First, the influence of direct activity from non-illuminated (nightside) areas of the comet and second, the brightness contribution of large gravity-dominated particles in the innermost coma. For our numerical simulations, we used a combination of DSMC gas dynamics simulation and particle propagation by an equation of motion to simulate the dust coma. Our simulations show that direct activity from the nightside is preferred, contributing ≈ 10% of the total emission. We show that intensity profiles, used to quantify dust outflow behaviour, fit the observations better when nightside activity is present and we suggest that nightside gas emission by CO 2 or CO is responsible for the observed dust flux. With the help of a simplified Keplerian modelling approach we exclude large particles on gravitationally bound or ballistic orbits from being the major contributor to the observed dust coma brightness. Additionally, we show the DS:NS ratio as a function of days to perihelion and observe that it is on a similar level as in the April OSIRIS time series from February to mid-June 2015, but increases towards a maximum of ≥ 4 . 07 ± 0.49 shortly after perihelion passage. We suggest that this is correlated to the increasing importance of H 2 O production when approaching perihelion. |
| Databáze: | OpenAIRE |
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