Context. Since its rendezvous with comet 67P/Churyumov-Gerasimenko (67P), the Rosetta spacecraft has provided invaluable information
contributing to our understanding of the cometary environment. On board, the VIRTIS and ROSINA instruments can both
measure gas parameters in the rarefied cometary atmosphere, the so-called coma, and provide complementary results with remote
sensing and in situ measurement techniques, respectively. The data from both ROSINA and VIRTIS instruments suggest that the
source regions of H2O and CO2 are not uniformly distributed over the surface of the nucleus even after accounting for the changing
solar illumination of the irregularly shaped rotating nucleus. The source regions of H2O and CO2 are also relatively different from one
another.
Aims. The use of a combination of a formal numerical data inversion method with a fully kinetic coma model is a way to correlate and
interpret the information provided by these two instruments to fully understand the volatile environment and activity of comet 67P.
Methods. In this work, the nonuniformity of the outgassing activity at the surface of the nucleus is described by spherical harmonics
and constrained by ROSINA-DFMS data. This activity distribution is coupled with the local illumination to describe the inner boundary
conditions of a 3D direct simulation Monte-Carlo (DSMC) approach using the Adaptive Mesh Particle Simulator (AMPS) code
applied to the H2O and CO2 coma of comet 67P.
Results. We obtain activity distribution of H2O and CO2 showing a dominant source of H2O in the Hapi region, while more CO2
is produced in the southern hemisphere. The resulting model outputs are analyzed and compared with VIRTIS-M/-H and ROSINADFMS
measurements, showing much better agreement between model and data than a simpler model assuming a uniform surface
activity. The evolution of the H2O and CO2 production rates with heliocentric distance are derived accurately from the coma model
showing agreement between the observations from the different instruments and ground-based observations.
Conclusions. We derive the activity distributions for H2O and CO2 at the surface of the nucleus described in spherical harmonics,
which we couple to the local solar illumination to constitute the boundary conditions of our coma model. The model presented
reproduces the coma observations made by the ROSINA and VIRTIS instruments on board the Rosetta spacecraft showing our understanding
of the physics of 67P’s coma. This model can be used for further data analyses, such as dust modeling, in a future work.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/614711 |
| Date | 30 March 2016 |
| Creators | Fougere, N., Altwegg, K., Berthelier, J.-J., Bieler, A., Bockelée-Morvan, D., Calmonte, U., Capaccioni, F., Combi, M. R., De Keyser, J., Debout, V., Erard, S., Fiethe, B., Filacchione, G., Fink, U., Fuselier, S. A., Gombosi, T. I., Hansen, K. C., Hässig, M., Huang, Z., Le Roy, L., Leyrat, C., Migliorini, A., Piccioni, G., Rinaldi, G., Rubin, M., Shou, Y., Tenishev, V., Toth, G., Tzou, C.-Y. |
| Contributors | Univ Arizona, Lunar & Planetary Lab |
| Publisher | EDP SCIENCES S A |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | © ESO 2016 |
| Relation | http://www.aanda.org/10.1051/0004-6361/201527889 |
Page generated in 0.0023 seconds