O seismometer of the module understandingwhich landed on Mars in 2018, detected the vibrations of four meteoroid collisions against the Martian surface in 2020 and 2021. Then, NASA’s Mars Reconnaissance Orbiter spacecraft tracked and was able to locate the associated craters.
The study results are published this week in the journal Geoscience of Nature and represent the first seismic and acoustic wave detections of impacts on another planet that are linked to its original craters. The distance at which Insight recorded the collisions ranged from 85 to 290 kilometers, in a region of Mars called Elysium Planitia, and the diameter of the craters ranged from 4 to 12 meters.
The first of four confirmed meteoroids – a term used to designate space rocks before they hit the ground, after which they are meteorites – made the most spectacular entry: it entered the Martian atmosphere in September 5, 2021exploding into at least three fragments, each leaving a crater.
So he Mars Reconnaissance Orbital confirmed the location of the space impact. He first used his black-and-white contextual camera to discover three dark spots on the surface, and then the High Resolution Imaging Science Experiment (HiRISE) camera took a color close-up of the craters.
These craters were formed by the impact of a meteorite on Mars on September 5, 2021, whose waves were detected by the InSight module. The image was taken by the Mars Reconnaissance Orbiter and has been color enhanced to highlight dust and ground disturbed by the impact (shown in blue). / NASA/JPL-Caltech/University of Arizona
This information prompted a review of previous data collected by the instruments, and so the scientists verified that another three meteorite impacts occurred (they fell to the surface and created craters) on May 27, 2020, February 18, 2021, and August 31, 2020. 2021.
Entry into the atmosphere and collision with the surface of a high-speed meteoroid generate shock waves. The bigger the explosion, the more the sound waves tilt the ground, information that InSight records and allows its direction to be analyzed. The authors used this data and arrival times to calculate the locations of the four events and request confirmation from the Mars Reconnaissance Orbiter.
“These waves are mainly created by the meteoroid impact on the ground, which generates both ground vibrations and therefore seismic waves, as an explosion in the atmosphere and therefore acoustic waves”, explains the lead author to SINC. Rafael Garciafrom the Higher Institute of Aeronautics and Space of Toulouse (France) and that this week participates in the Europlanet Science Congress (EPSC 2022), which is celebrated in Granada.
“We feel the seismic waves with the seismometer, which monitors the vibrations of the ground (they arrive first at InSight), but it can also measure the deformations of the ground induced by the pressure variations of the acoustic waves that pass over it”, he adds. We use the ground as the membrane of a microphone that moves under variations in acoustic pressure.”
According to Garcia, this study is important “because it provides seismic sources with known exact location, which will be used to obtain better images of the crust of Mars (first 50 km of the planet below the surface); and it will also offer scale relationships, between a given crater size and the amount of seismic and acoustic waves created by impacts, which can also be used on other planets.”
The science behind the impacts
Researchers wonder why they haven’t detected more meteorite impacts on Mars. The red planet lies adjacent to the solar system’s main asteroid belt, which provides an ample supply of space rocks to mark the planet’s surface. As the atmosphere of Mars is only 1% thicker than that of Earth, there is more meteoroids that pass through it without disintegrating.
The seismic data offers several clues that will help researchers better understand the Red Planet. Most earthquakes on Mars are caused by underground rocks separating from heat and pressure. Studying how the resulting seismic waves change as they travel through different materials gives scientists a way to study the planet’s crust, mantle, and even the core.
The four meteoroid impacts confirmed so far have produced small earthquakes of magnitude not greater than 2.0. These smaller quakes only provide a glimpse of the Martian crust, while seismic signals from larger quakes such as the magnitude 5 event that occurred in May 2022 can also reveal details about the mantle and core.
These collisions will be critical to adjusting the timing of Mars. “Impacts are the clocks of the solar system”, comments García, “we need to know the current impact rate to estimate the age of the different surfaces”.
Researchers can approximate the age of a planet’s surface by counting its impact craters: the more they see, the older the surface. By calibrating their statistical models based on the frequency of current impacts, they can estimate how many shocks have occurred at earlier times in the solar system’s history.
The InSight seismometer has detected more than 1,300 Martian earthquakes. Provided by the Center National d’Études Spatiales (CNES, the French space agency), this instrument is so sensitive that it can record seismic waves thousands of kilometers away. It is suspected that there may be hidden collisions between the collected data due to wind noise or seasonal changes in the atmosphere.
The probe still has time to study Mars. Dust buildup on the probe’s solar panels is reducing its power and will eventually cause the spacecraft to shut down. It’s hard to predict exactly when, but based on the latest power readings, engineers believe it could shut down between October this year and January 2023.
Reference:
Rafael Garcia et al. “Newly formed craters on Mars located using InSight seismic and acoustic wave data”. Geoscience of Nature2022