New craters are created on planetary surfaces by meteorite impacts, which also change the atmosphere’s makeup. Meteoroids cause brief seismic and acoustic waves to be generated during atmospheric entry and ground impact. However, new crater formation and related impact-induced mechanical waves have not yet been observed jointly beyond Earth.
In a new study, NASA reported observations of seismic and acoustic waves from the NASA InSight lander’s seismometer. The observations are linked to the four meteoroid impact events on Mars observed in spacecraft imagery. The impacts ranged between 53 and 180 miles (85 and 290 kilometers) from InSight’s location, a region of Mars called Elysium Planitia.
The first of the four confirmed meteoroids, the term for space rocks before they impact the ground, made the most dramatic entrance: It impacted Mars’ atmosphere on September 5, 2021, bursting into at least three shards that each left a crater in its behind.
Then, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site to confirm the location. Its black-and-white Context Camera revealed three darkened spots on the surface. The orbiter’s team utilized the HiRISE camera to obtain a color close-up of the craters after they had located these places.
Ingrid Daubar of Brown University, a paper’s co-author and a specialist in Mars impacts, said, “After three years of InSight waiting to detect an impact, those craters looked beautiful.”
After analyzing earlier data, scientists confirmed three other impacts had occurred on May 27, 2020; Feb. 18, 2021; and Aug. 31, 2021.
Why there haven’t been more meteoroid collisions on Mars has baffled researchers. The primary asteroid belt of the solar system is just next to the Red Planet, which means there are enough space rocks nearby to scour the planet’s surface. Because Mars’s atmosphere is just 1% thicker than Earth’s, more meteoroids pass through it without disintegrating.
InSight’s seismometer has detected over 1,300 marsquakes. The instrument is so sensitive that it can detect seismic waves from thousands of miles away. But the Sept. 5, 2021, event marks the first time an impact was confirmed as the cause of such waves.
InSight’s team suspects that “other impacts may have been obscured by wind noise or seasonal changes in the atmosphere. But now that the distinctive seismic signature of an impact on Mars has been discovered, scientists expect to find more hiding within InSight’s nearly four years of data.”
Seismic data provide numerous hints that will improve scientists’ understanding of the Red Planet. Most marsquakes are triggered by pressure and heat-induced breaking of underlying rocks. Scientists can analyze Mars’ crust, mantle, and core by observing how seismic waves alter as they pass through various materials.
The four meteoroid impacts confirmed so far produced small quakes with a magnitude of no more than 2.0. Those more minor quakes provide scientists with only a glimpse into the Martian crust, while seismic signals from larger quakes, like the magnitude 5 event that occurred in May 2022, can also reveal details about the planet’s mantle and core.
Paper’s lead author, Raphael Garcia of Institut Supérieur de l’Aéronautique et de l’Espace in Toulouse, France, said, “But the impacts will be critical to refining Mars’ timeline. Impacts are the clocks of the solar system. We need to know the impact rate today to estimate the age of different surfaces.”
By counting the number of impact craters present on a planet’s surface, scientists can determine the age of the planet’s surface. Scientists can then determine how many more impacts occurred earlier in the solar system’s history by calibrating their statistical models depending on how frequently they observe impacts happening.
A meteoroid’s trajectory and shock wave size may be recreated using information from InSight and orbital pictures. Every meteoroid produces an explosion when it strikes the Earth and a shock wave when it strikes the atmosphere. Sound waves from these incidents travel across the atmosphere. When this sound wave reaches InSight, the ground is tilted more dramatically the larger the explosion. The seismometer on the lander is sensitive enough to measure how much and in what direction the ground tilts as a result of such an event.
Garcia said, “We’re learning more about the impact process itself. We can now match different craters sizes to specific seismic and acoustic waves.”