Images of the nucleus and the coma ( gas and dust ) of comet 67P/Churyumov- Gerasimenko have been acquired by the OSIRIS ( Optical , Spectroscopic , and Infrared Remote Imaging System ) cameras since March 2014 using both the Wide Angle Camera ( WAC ) and the Narrow Angle Camera ( NAC ) .
We use images from the NAC camera to study a bright outburst observed in the southern hemisphere on July 29 , 2015 .
The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus .
The heliocentric distance is 1.25 au and the spacecraft-comet distance is 186 km .
Aiming to better understand the physics that led to the outgassing , we used the Direct Simulation Monte Carlo ( DSMC ) method to study the gas flow close to the nucleus and the dust trajectories .
The goal is to understand the mechanisms producing the outburst .
We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region .
The outburst is in fact a combination of both gas and dust , in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas .
We need a number of dust particles 7.83 \times 10 ^ { 11 } - 6.90 \times 10 ^ { 15 } ( radius 1.97 - 185 \mu m ) , which corresponds to a mass of dust 220 - 21 \times 10 ^ { 3 } kg .