InSight finds high meteoroid impact rate on Mars

Scientists have long sought to determine the rate of meteoroid impacts on Mars, employing two primary methods before the availability of seismic data. One approach involved calculating the impact rate from lunar crater chronology models, which are based on studies of craters on the Moon and adjusted to account for Mars’ atmosphere and proximity to the asteroid belt.

The other method involved analyzing images captured by orbiting satellites, either by comparing before-and-after images to identify new craters or by detecting the dark areas characteristic of recent impact zones, as the disturbed dust appears darker than the surroundings before fading over time. However, this method has limitations, as the resolution of the cameras prevents detection of craters below a certain size, and craters can be obscured by dust storms or the surrounding landscape.

These two methods have yielded different results, with the Moon-based estimates being substantially higher than those based on orbital images. The limitations of orbital imaging have made it challenging to accurately measure the meteoroid impact rate on Mars.

The seismic data from NASA’s InSight lander has provided a new opportunity to calculate the impact rate more precisely. Two companion studies published in June 2022 utilized InSight’s seismic measurements to independently estimate the meteoroid impact rate on Mars:

• A team led by Ingrid Daubar of Brown University extrapolated the impact rate from meteoroid impacts detected by InSight’s Seismic Experiment for Interior Structure (SEIS). Using this method, they found an impact rate two to ten times higher than previously determined using other methods.

• A team led by Géraldine Zenhäusern of ETH Zurich, Switzerland, and Natalia Wójcicka of Imperial College London, United Kingdom, considered the possibility that all very-high-frequency (VF) seismic events observed by InSight were caused by meteoroid impacts. Using two different strategies, they estimated an impact rate of 280 to 362 impacts per year, forming craters greater than 8 meters in diameter.

Both studies independently found substantially higher impact rates than those calculated from orbital imaging, aligning more closely with the Moon-based estimates. These results suggest that seismic measurements offer a more effective method for studying meteoroid impacts on Mars than relying solely on orbital imagery.

To estimate the meteoroid impact rate on Mars using seismic data from InSight, the two teams employed different but complementary methodologies.

The team led by Ingrid Daubar focused on the eight specific meteoroid impacts detected by InSight’s Seismic Experiment for Interior Structure (SEIS). Six of these impacts were located near the lander, while the other two were much farther away but among the largest ever detected in the Solar System.

By analyzing the seismic signatures of these eight craters, Daubar’s team could extrapolate the overall impact rate on Mars. Their approach considered the size and frequency of the impacts, as well as the limited detection range of InSight’s seismometer.

On the other hand, the team led by Géraldine Zenhäusern and Natalia Wójcicka took a broader approach. They observed that all six impacts near InSight were categorized as very-high-frequency (VF) seismic events, which are Marsquakes occurring much faster than tectonic events.

Zenhäusern and Wójcicka hypothesized that all VF events detected by InSight could be attributed to meteoroid impacts. They first estimated the crater diameters based on the magnitudes and distances of the VF events. Then, they calculated the number of impacts around InSight over the course of a year and extrapolated this data to estimate the annual impact rate for the entire surface of Mars.

Both teams employed different strategies to interpret the seismic data, but their independent estimates aligned closely, lending credibility to their findings. The seismic data provided a more comprehensive picture of the meteoroid impact rate, overcoming the limitations of orbital imaging and offering a new tool for studying these events on Mars.