The near nucleus gas and dust environment around comet 67P/Churyumov-Gerasimenko

The Rosetta mission to comet 67P/C-G provided a detailed view of the near nucleus environment of an active Jupiter family comet. The continuous monitoring of the gas pressure with the ROSINA experiment at the location of the Rosetta spacecraft in combination with the images of the dust environment acquired by the OSIRIS cameras allows one to test different hypotheses about the origin of the dust and gas emissions. In addition the orbital elements and the rotation axis and spin rate of the nucleus are affected by the gas release.

The dust and gas emission around the nucleus of comet 67P/C-G displays a very repetitive pattern in time and space [1,2], with additional short-lived (< 30 min) localized outbursts of activity, in particular around perihelion [3].

We present an overall assessment of the gas emission of comet 67P/C-G based on (i) connecting the ROSINA gas measurements to surface activity and (ii) based on the observed changes in the orbital and rotational state vector [4,5], including the 2021/22 MPEC data set for the astrometry.

One important tool is our use of a detailed shape-based model to constrain the gas and dust emission. We describe two limiting cases for which analytic solutions of the gas field are obtainable: (1) a rarefied gas emission with non-interacting gas flows and (2) an incompressible flow field. We discuss their implications for the dust lift-off from the surface of the nucleus. We estimate the velocity of the dust propelled by the gas from the Coriolis deflection. The deflection and dust velocity is accessible from the OSIRIS data by looking at the curvature of the observed dust streams.

We systematically discuss uncertainties in the data analysis and point out open questions regarding the choice of boundary and initial conditions for the modeling of the coma around the nucleus. The surface composition of the nucleus in terms of 14 volatiles for 67P/C-G is shown as surface distribution maps [6,7], which provides a baseline for the comparison with other comets and active gas and dust emitting objects.

References:

1. Kramer, T. & Noack, M. On the Origin of Inner Coma Structures Observed by Rosetta during a Diurnal Rotation of Comet 67P/Churyumov–Gerasimenko. ApJL 823, L11 (2016).

2. Kramer, T., Noack, M., Baum, D., Hege, H.-C. & Heller, E. J. Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov–Gerasimenko. Advances in Physics: X 3, 1404436 (2018).

3. Vincent, J.-B. et al. Summer fireworks on comet 67P. Monthly Notices of the Royal Astronomical Society 462, S184–S194 (2016).1. Kramer, T. & Noack, M. On the Origin of Inner Coma Structures Observed by Rosetta during a Diurnal Rotation of Comet 67P/Churyumov–Gerasimenko. ApJL 823, L11 (2016).

4. Kramer, T. et al. Comet 67P/Churyumov-Gerasimenko rotation changes derived from sublimation-induced torques. Astronomy & Astrophysics 630, A3 (2019).

5. Kramer, T. & Läuter, M. Outgassing-induced acceleration of comet 67P/Churyumov-Gerasimenko. Astronomy & Astrophysics 630, A4 (2019).

6. Kramer, T., Läuter, M., Rubin, M. & Altwegg, K. Seasonal changes of the volatile density in the coma and on the surface of comet 67P/Churyumov–Gerasimenko. Monthly Notices of the Royal Astronomical Society 469, S20–S28 (2017).

7. Läuter, M., Kramer, T., Rubin, M. & Altwegg, K. The Ice Composition Close to the Surface of Comet 67P/Churyumov-Gerasimenko. ACS Earth Space Chem. acsearthspacechem.1c00378 (2022) doi:10.1021/acsearthspacechem.1c00378.