What does a meteorite sound like when it falls on Mars?

The seismometer of the module Insight, that landed on Mars in 2018, has detected the vibrations of four collisions of meteoroids against the Martian surface in 2020 and 2021. After the spacecraft Mars Reconnaissance Orbiteralso from NASA, has tracked and managed to locate the associated craters.

The results of the study are published this week in the journal Nature Geoscience and they represent the first detections of seismic and acoustic waves from impacts on another planet that are linked to their 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 the four confirmed meteoroids – a term used to designate space rocks before they hit the ground, after which they are meteorites – made the most spectacular entrance: it entered the Martian atmosphere September 5, 2021, exploding into at least three fragments each leaving a crater.

Then he Mars Reconnaissance Orbiter confirmed the impact site from space. 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 camera (HiRISE) got a color close-up of the craters.

This information encouraged a review of the previous data collected by the instruments, and thus the scientists verified that three other meteorite impacts (fragments that fell to the surface and created craters) had occurred on May 27, 2020, on February 18, 2020. 2021 and August 31, 2021.

Mars

The entry into the atmosphere and the collision on the surface of a meteoroid at high speed generates shock waves. The larger the explosion, the more the sound waves tilt the ground, information that InSight records and allows its direction to be analysed. The authors used these data and arrival times to estimate the locations of the four events and request confirmation from the Mars Reconnaissance Orbiter.

“These waves are created mainly by the impact of the meteoroid on the ground, which generates both vibrations in it, and therefore seismic waves, as well as an explosion in the atmosphere, and therefore acoustic waves”the main author explains to SINC, Rafael Garcia, of the Higher Institute of Aeronautics and Space in 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 ground vibrations (they come to InSight first), but can also measure ground deformations induced by pressure variations of the acoustic waves passing over him -Add-. 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 locationwhich will be used to obtain better images of the crust of mars (first 50 km of the planet below the surface); and also contributes relationships, between a given crater size and the amount of waves seismic and acoustic properties created by the 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. Since Mars’ atmosphere is only 1% thicker than Earth’s, 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 subsurface rocks breaking apart 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 core.

The four confirmed meteoroid impacts so far produced small earthquakes of a magnitude not greater than 2.0. Those smaller tremors provide only a glimpse of the Martian crust, while seismic signals from larger tremors, 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 in fine-tuning the chronology of Mars. “Impacts are the clocks of the solar system”Garcia comments, “we need to know the current impact rate to estimate the age of the different surfaces”.

Approximating the surface age of a planet

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 more shocks occurred at earlier times in the solar system’s history.

InSight’s seismometer has already detected more than 1,300 Martian earthquakes. provided by the Center National d’Etudes 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 data you have collected due to wind noise or seasonal changes in the atmosphere.

The lander still has time to study Mars. Dust buildup on the lander’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 energy readings, engineers believe it could be turned off between October this year and January 2023.

Font: Enrique Sacristán / SINC Agency

Reference article: https://www.agenciasinc.es/Noticias/Asi-se-escucha-un-meteorito-al-caer-en-Marte