| Popis: |
The crater density on planetary surfaces is used to determine their ages throughout the solar system, which requires a model for the rate of meteorite impacts of different sizes. For craters smaller than 30 meters, this rate has been observed from the generation of new craters in repeated orbital images. For larger craters, the rate was extrapolated from the lunar surface ages, taking into account the atmospheric removal of small craters. It has been observed that both estimates do not match for crater diameters smaller than 30 meters. The NASA InSight seismometer SEIS provided a new independent constraint, when it recorded seismic signals of several impacts during its mission. These confirmed impacts are part of a larger class of marsquakes (Very High Frequency, VF), all of which have characteristics consistent with an impact origin. We show that these VFs are plausibly caused by meteorite impacts and derive the impact rate required to explain their numbers. An empirical scaling relationship is used to convert between seismic moment and crater diameter. We apply area and time corrections to derive a global impact rate and find that the derived rate is 210--290 craters >8m globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters. |
