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Mars’ Crater Impact Rate Gets an Update with the Help of Seismic Data

Tags: earthquakes , seismic , seismology

Counting the number of craters on rocky (or icy) Solar System bodies is one way planetary scientists try to estimate the age of the surface and build out a history of our small pocket of the galaxy. Generally, the greater the number of craters, the older the surface. Crater counting is one way we’ve studied the best-explored member of the planetary family: Mars. 

In 2021, the NASA InSight lander made planetfall with the goal of detecting Martian seismic signals, called marsquakes. InSight has advanced our understanding of the Martian interior by using seismic techniques typically applied on Earth. (In fact, InSight’s data can be accessed in the NSF SAGE archive operated by EarthScope.) One instrument, the Seismic Experiment for Interior Structure (SEIS) returned data that shows marsquakes from recent impacts of space debris on the surface. Compared to the orbitally-imaged catalog of craters, the seismically-detected events don’t seem to entirely match. 

Multi-paneled images of craters from an aerial perspective. The craters are false-colored so that some debris ejecta appear blue or purple. Scale bars denote the diameter of craters, which appear between 20 meters and 200 meters.
High Resolution Imaging Science Experiment images of new impact craters on Mars taken with the Mars Reconnaissance Orbiter. Color modified to highlight craters. (Credit: Daubar et al. 2024; Science Advances; NASA/JPL/University of Arizona.)

Crater-counting of the martian surface is typically done with cameras and detectors on orbiters such as the Mars Reconnaissance Orbiter (MRO), but can be limited due to resolution of images. New craters are identified by taking multiple images of the same part of the surface over time and checking to see if any new craters have appeared. Low resolution means that not all craters are detected. This process is also typically done manually, so some impact events might risk being missed. 

In a new study published in Science Advances, six new craters on Mars are examined. These new additions are examined in two datasets: the first consists of craters identified by using both the InSight seismic instrument and the imaging camera on MRO, while the second dataset relies only on MRO orbital imaging. Comparing these datasets helped the researchers understand if seismic data performed any better at identifying impact events and locating them. 

Using the InSight Lander seismic data allowed researchers to estimate how far away the cratering events were from the lander, and in what directions, so researchers knew approximately where they needed to look in the MRO images to find evidence of an impact. 

Using these new detections, the team was able to convert the craters into an annual cratering rate based on their different diameters. This provides an understanding of how often objects of different sizes hit the Martian surface. But when the team compared their snapshot cratering rate to the previously established number, they found a discrepancy. The dataset incorporating detections from InSight seemed to suggest a higher rate for objects with a diameter of 10 meters or more, meaning that objects were falling to the Martian surface more often than had been previously detected with just MRO images. Encouragingly, this higher impact rate agrees with models that factor in the effect of Mars’ thin atmosphere on an object’s entry trajectory.

A finding like this would indicate our crater-based age estimates could be off by as much as a factor of 2 to 10. If accurate, the use of seismic data alongside the traditional orbital images may allow for better crater counting, thus improving estimates of the age of the Solar System.

Two-paneled figure showing impact rate from different instruments on Mars. Green circles show the recent impacts factored into the calculation, while brown squares both filled and unfilled show prior data. A red triangle and a purple triangle show impacts that are far away from InSight Lander.
Estimated impact rates on Mars using the InSight seismic data and camera on Mars Reconnaissance Orbiter. The green circles indicate the new cratering data from InSight, while the red and purple triangles showcase two distance impacts that were detected with InSight. The open brown squares are an updated orbital imaging dataset, while the closed brown squares refer to the prior dataset. The dotted lines refer to two prior estimates of cratering rates. Left: The annualized cumulative impact rate, representing the historical impact rate. Right: The annualized differential impact rate representing a snapshot of impact rate.

But researchers utilizing this joint approach have to be careful. The higher rate of cratering could be a temporary uptick from an object in space deteriorating in orbit or crashing into one of Mars’ two moons (Deimos & Phobos), ejecting space litter. Moreover, using the seismic data to search for a crater visually is also imperfect—evidence of a crater could be too small to spot, or it could be hidden by a nearby topographic feature. This would mean that even though a clear signal could be detected, it would be difficult or impossible to verify visually. Lastly, it is still possible that some of the seismic signals detected come from some unidentified process rather than an impact, opening the door for further exploration into what InSight seismic data has to offer. 

This new work using InSight’s seismic data highlights the need to more comprehensively detect impact craters. Creative approaches to analyzing craters in MRO images (like automated machine learning algorithms) have been put forth, which could complement a seismic dataset from InSight and a visual cache from MRO.

A combined geophysical and orbital approach to investigating the planetary surface processes of Solar System bodies provides a unique way to probe their history. Implementing this joint process on other planetary environments, like Venus or faraway Saturnian moon Titan, could be on the horizon.