Mars meteorite impact rate uncovered by new study using NASA’s InSight

A new study combined orbital imagery with seismological data from NASA’s Mars InSight lander to derive a new impact rate for meteorite strikes on Mars.

In a study published in Nature Astronomy, researchers have provided new insights into the meteoroid impact rate on Mars by utilizing seismic data recorded by the InSight lander.

Since its deployment on Mars, NASA’s InSight lander has been recording marsquakes, among other seismic activities. The data from InSight’s seismometer has enabled scientists to estimate the impact rate on Mars more accurately than ever before. The study, “An estimate of the impact rate on Mars from statistics of very-high-frequency marsquakes,” was led by G. Zenhäusern, N. Wójcicka, and S.C. Stähler.

The traditional method of determining the age of planetary surfaces relies on counting impact craters. For smaller craters, especially those less than 60 m (197 feet) in diameter, previous estimates on Mars derived from orbital imagery or extrapolated from lunar impact data have been inconsistent. This discrepancy prompted researchers to seek an independent and reliable method for calculating the production rate of these craters.

By analyzing seismic events recorded by InSight, the team identified a class of very-high-frequency (VF) marsquakes, which they propose are likely caused by meteorite impacts. “Some previously confirmed seismically detected impacts are part of a larger class of marsquakes (very-high-frequency, VF). Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts,” the researchers stated.

To convert seismic data into impact rates, the scientists applied an empirical scaling relationship. This technique involves converting seismic moment measurements to crater diameters, providing a robust estimate of how many new craters are formed over time. They found that globally, Mars experiences between 280 to 360 new craters over 8 m (26 feet) in diameter each year.

“Applying area and time corrections to derive a global impact rate, we find that 280 – 360 craters which are over 8 m (26 feet) in diameter are formed globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters,” confirmed the study.

These findings complement previous methodologies, confirming the validity of using orbital imagery while also showcasing the effectiveness of seismic data.

“Our work shows that seismology is an effective tool for determining meteoroid impact rates and complements other methods such as orbital imaging,” the researchers said.

InSight’s mission has been a significant contributor to these findings. The lander recorded seismic data for over 3.17 years until June 2022. The researchers took into account the seasonal variability of Martian background noise, which could affect the detection counts of seismic events. They noted, “More VF events were detected in Martian year 2 of the InSight mission than year 1 (as have other event types). However, taking the seasonal variability of the background noise into account, the differences in detection counts between year 1 and year 2 are within one standard deviation of what would be expected for an event rate that is constant during the whole time as a Poisson process.”

This study further categorizes VF events, distinguishing them from high-frequency (HF) events, which exhibit strong seasonal variability. This differentiation is crucial for understanding the underlying causes and accurately counting the corresponding craters.

One of the key aspects of their approach involves the impact momentum scaling. The researchers detailed how seismic moment scales with impact momentum and crater diameter.

“As demonstrated in Garcia et al., the resulting scaling relationship is (numerically substituted equation). Numerical modeling studies have shown that the seismic moment M0 scales linearly with the impact momentum and as a power law with crater diameter M0 = cDn, where n varies between 3.0 and 3.6 depending on target material properties. For this work, we chose n = 3.3 to represent an average between a strongly cohesive material and a cohesionless sand,” the researchers said.

This relationship helps map the distance at which a crater impact would be detectable by InSight, enhancing the precision of their estimates. “The impact detectability curve can, therefore, be defined as the maximum distance at which a crater of diameter D would be detectable by InSight,” the study explains.

The research’s implications extend to determining accurate absolute ages of surfaces across the Solar System. The impact rate on Mars serves as a critical reference point for age calculations, aiding in the comparative studies of surfaces on the Moon, Earth, and other planetary bodies.

The empirical scaling relationships provide a nuanced view of the VF events’ detectability and their cause. The team noted the significance of the vertical offset in the log-log plot for the detectability curve, which is set to match detectable crater diameters defined by detection curves for VF events. Specifically, at a distance of 1 000 km (620 miles), this curve returns a crater diameter of 6.4 m (21 feet), marking a precise calculation tied to the detected seismic amplitudes.

The counting of high-frequency marsquakes aligns with the constant event rates anticipated under Poisson processes. Such consistency over multiple Martian years attests to the reliability of the seismic data-driven approach, contrasting the seasonal variability found in high-frequency seismic events.

¹ An estimate of the impact rate on Mars from statistics of very-high-frequency marsquakes – Géraldine Zenhäusern et al.- Nature Astronomy- – OPEN ACCESS

Featured image credit: These craters were formed by a September 5, 2021, meteoroid impact on Mars, the first to be detected by NASA’s InSight. Taken by NASA’s Mars Reconnaissance Orbiter, this enhanced-color image highlights the dust and soil disturbed by the impact in blue in order to make details more visible to the human eye. Credits: NASA/JPL-Caltech/University of Arizona