Applying the knowledge of terrestrial fireballs to Mars

All bodies in our solar system are affected by impact processes. On bodies with atmosphere, an impactor (i.e., meteoroid, asteroid or comet) experiences aerodynamic resistance, slows down and breaks up if the dynamic atmospheric pressure surrounding the impactor is higher than the impactor's compressive strength (Cevolani, 1994; Stevanović et al., 2017). On Earth, an average height the terrestrial airbursts occur is about 35 km (Bland \& Artemieva, 2006). This is high enough in our atmosphere to prevent frequent formation of crater clusters on Earth. However, the surface density of Mars' atmosphere is comparable to that of the Earth at an altitude of $\sim$35 km. On Mars, about 50% of small impacts form a cluster crater and the other half forms single craters (Daubar et al., 2013, 2015). Crater clusters have likely formed due to fragmentation of an impactor relatively close to the ground. In this study, we use data from the Desert Fireball Network (DFN) and results from the analysis of seismic signals from fireballs, to apply the knowledge of terrestrial fireballs to the physical conditions in the Martian atmosphere. The DFN is the world's largest network of camera observatories aimed to detect fireballs, calculate their orbits and recover meteorites (Devillepoix et al., 2018, 2019). Data from images using triangulation, gives information about the time, duration, velocities, heights of the begin and end of the bright flight and maximum peak brightness of these observed fireballs (Devillepoix et al., 2019; Howie et al., 2017). From these results information about fragmentation processes can be obtained through determination of the maximum peak brightness of these fireballs in combination with the analysis of recorded images and videos. Data from the DFN shows that the beginning of the bright flight takes place at about 90 km and the end of the bright flight is between 50 and 60 km. Fragmentation may occur towards the end of the bright flight, that can be accompanied by an airburst detectable within 200 km distance. It is, however, more common for passing fireballs to move at supersonic speeds, therefore causing the formation of the Mach cone that in itself can produce an atmospheric disturbance detectable by seismic stations positioned on its trajectory. In November 2018, NASA's mission InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) landed on Mars and deployed the instrument SEIS (Seismic Experiment for Interior Structure) onto the surface. SEIS consists of a 3-component very broad band and a 3-component short period seismometer (Lognonné et al., 2018) to detect seismic signals from impacts and marsquakes. One of the aims of the mission is to get more information about the current impact rate on Mars. To contribute to this aim, it is important to understand the fragmentation of meteoroids on Mars.