Frontiers in Physics, 24 June 2020, Volume 8, p. 227, https://doi.org/10.3389/fphy.2020.00227

## The dust-to-gas ratio, size distribution, and dust fall-back fraction of comet 67P/Churyumov-Gerasimenko: Inferences from linking the optical and dynamical properties of the inner comae.

#### Raphael Marschall, Johannes Markkanen, Selina-Barbara Gerig, Olga Pinzón-Rodríguez, Nicolas Thomas, and Jong-Shinn Wu

This page contains interactive plots of the above-mentioned paper. Each interactive plot can be customised by changing the axis rages via the leavers at the top and right. By selecting different options in the legend the displayed data can be changed. Via the menu at the top left of each chart, the data can be downloaded and the current view saved as an image.

For all details on the figures please consult the paper. Here you can download the paper . The abstract can be found below.

There are 7 interactive charts on this page comprising the following figures in the paper:

Figure 1: Shows the sub-solar latitude of comet 67P as a function of heliocentric distance.

Figure 2: Shows the scattering phase function for different dust sizes.

Figure 7: Shows the dust-to-gas ration as a function of the power-law index for different minimum dust sizes and different dust bulk densities.

Figure 8: Shows the amount of dust fall back as a function of the gas activity and dust size power-law exponent.

Figure 9: Shows the largest liftable and largest escaping dust sizes as a function of the gas activity.

Figure 10: Shows the total escaping dust mass as a function of the dust size power law.

Figure 11: Shows the global gas and dust production rates as a function of time.

If you use the data or charts presented here please reference the paper: Marschall et al., 2020, Frontiers in Physics, vol. 8, p. 227, https://doi.org/10.3389/fphy.2020.00227.

#### Abstract

In this work, we present results that simultaneously constrain the dust size distribution, dust-to-gas ratio, fraction of dust re-deposition, and total mass production rates for comet 67P/Churyumov-Gerasimenko. We use a 3D Direct Simulation Monte Carlo (DSMC) gas dynamics code to simulate the inner gas coma of the comet for the duration of the Rosetta mission. The gas model is constrained by ROSINA/COPS data. Further, we simulate for different epochs the inner dust coma using a 3D dust dynamics code including gas drag and the nucleus’ gravity. Using advanced dust scattering properties these results are used to produce synthetic images that can be compared to the OSIRIS data set. These simulations allow us to constrain the properties of the dust coma and the total gas and dust production rates.

We determined a total volatile mass loss of $(6.1 \pm 1.5) \cdot 10^9 kg$ during the 2015 apparition. Further, we found that power-laws with $q=3.7^{+0.57}_{-0.078}$ are consistent with the data. This results in a total of $5.1^{+6.0}_{-4.9}\cdot10^9 kg$ of dust being ejected from the nucleus surface, of which $4.4^{+4.9}_{-4.2}\cdot10^9 kg$ escape to space and $6.8^{+11}_{-6.8}\cdot10^8 kg$ (or an equivalent of $14^{+22}_{-14} cm$ over the smooth regions) is re-deposited on the surface. This leads to a dust-to-gas ratio of $0.73^{+1.3}_{-0.70}$ for the escaping material and $0.84^{+1.6}_{-0.81}$ for the ejected material. We have further found that the smallest dust size must be strictly smaller than $\sim30\mu m$ and nominally even smaller than $\sim12\mu m$.

#### Figure 1

Heliocentric distance vs. sub-solar latitude of comet 67P during the escort phase of Rosetta. Time runs along the line from top right to bottom left and then back. Dates are included when downloading the data of this chart.

#### Figure 2

Shows the phase functions, S11 , at 612 nm (OSIRIS WAC18 filter) as a function of phase angle for different dust particle radii. Dust particles are considered to be irregular aggregates composed of sub-micrometer-sized organic grains and micrometer-sized silicate grains. The refractive index for silicate grains is assumed to be m = 1.6048692 + i0.0015341 corresponding to magnesium iron pyroxine [Dorschner et al. 1995] and for organic grains m = 1.55950 + i0.42964 corresponding to amorphous carbon [Jäger et al. 1998].

#### Figure 7

The dust-to-gas ratio is shown as a function of the power-law index. You can switch between comparing different minimum dust sizes, rmin, or the dust bulk density. For the comparison of the minimum dust sizes, the dust bulk density is set to 533 kg m-3. For the comparison of the dust bulk density, the minimum dust size is set to 0.01 μm.

For each of the comparisons, the gas activity can be varied between high [800 kg s−1, epoch 12, southern summer solstice] and low [35 kg s −1; epoch 6, inbound equinox].

#### Figure 8

The ratio of dust mass falling back, QDfb to total dust mass, QD is shown as a function of global gas production rate, Qg, for different power-law exponents.

#### Figure 9

The largest liftable dust size (red curve) and the largest escaping dust size (blue curve) are shown as a function of the gas production rate.

#### Figure 10

The total escaping dust mass, MDesc , is shown as a function of the power-law index for five different minimum dust radii, r_min . The horizontal dashed lines show the nominal ejected dust mass (green) and the maximum ejected dust mass (red). Any models above the dashed red line are incompatible with the total mass loss of comet 67P and can, therefore, be excluded as viable models.

#### Figure 11

Shows the global production rate for the gas (purple) and dust (green) as a function of days to perihelion. The bands indicate the range due to the diurnal variation. The gas production rates have been constrained by ROSINA/COPS measurements while the dust production rates are from combined constraints of OSIRIS and gas fluxes. For the dust a minimum size of r_min = 0.1 μm and power-law exponent of q = 3.75 are assumed.