Browsing by Author "Pinzon-Rodriguez, O."

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A comparison of multiple Rosetta data sets and 3D model calculations of 67P/Churyumov-Gerasimenko coma around equinox (May 2015)
(2019-08-01)
Marschall, R.
;
Rezac, L.
;
Kappel, D.
;
Su, C. C.
;
Gerig, S. -B.
We have used the latest available shape model for gas and dust simulations of the inner coma of comet 67P/Churyumov-Gerasimenko for the period around May 2015 (equinox). We compare results from a purely insolation-driven model with a complementary set of observations made by ROSINA, VIRTIS, MIRO, and OSIRIS within the same period. The observations include - for the first time - inverted MIRO measurements of gas density, temperature and bulk velocity to constrain the model. The comparisons show that, as in November 2014 (Marschall et al., 2016), insolation-driven activity does not provide an adequate fit to the data. Both VIRTIS and MIRO observations indicate that emissions from the Hatmehit and Imhotep regions of the nucleus are strongly depleted in total gas, H2O, and dust emissions in this case. The MIRO inversion provides a challenging constraint to the models as a consequence of the terminator orbit and nucleus pointing of the spacecraft. Nonetheless a consistent picture with a dominance of outgassing from the Hapi region, even at equinox, is clearly evident. An inhomogeneous model consistent with models proposed for the November 2014 time-frame was constructed and provides a better fit to the data. As far as we are aware this is the first time comae data from four Rosetta instruments have been used to constrain within one self-contained model the emission distribution at the nucleus surface and study the dynamics of the gas and dust outflow.
Dayside-to-nightside dust coma brightness asymmetry and its implications for nightside activity at Comet 67P/Churyumov-Gerasimenko
(2020-11-15)
Gerig, S-B
;
Pinzon-Rodriguez, O.
;
Marschall, R.
;
Wu, J-S
;
Thomas, N.
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 degrees 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 approximate to 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 CO2 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 H2O production when approaching perihelion.