NASA’s InSight lander detected seismic waves from four space rocks that crashed into Mars in 2020 and 2021. Not only do these represent the first impacts detected by the spacecraft’s seismometer since landing from InSight on the red planet in 2018, but it is also the first time seismic and acoustic waves from an impact have been detected on Mars.
A new paper published Monday in Nature Geoscience details the impacts, which ranged between 85 km and 290 km from InSight’s location, a region of Mars called Elysium Planitia.
The first of four confirmed meteoroids – the term used to refer to space rocks before they hit the ground – made the most spectacular entry: it entered Mars’ atmosphere on September 5, 2021, exploding in au minus three shards that each left a crater behind. .
Then, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site to confirm the location. The orbiter used its black-and-white pop-up camera to reveal three dark dots on the surface. After locating these points, the orbiter team used the High-Resolution Imaging Science Experiment, or HiRISE, camera to get a color close-up of the craters (the meteoroid could have left additional craters on the surface, but they would be too small to see in the HiRISE images).
“After three years of waiting for InSight to detect an impact, these craters were magnificent,” said Ingrid Daubar of Brown University, co-author of the paper and Mars impact expert.
After combing through past data, scientists confirmed that three more impacts occurred on May 27, 2020; February 18, 2021; and August 31, 2021.
Researchers wonder why they haven’t detected more meteorite impacts on Mars. The red planet sits next to the solar system’s main asteroid belt, which provides enough space rock to scar the planet’s surface. Because Mars’ atmosphere is only 1% thicker than Earth’s, more meteoroids pass through it without disintegrating.
InSight’s seismometer has detected more than 1,300 Marchquakes. Provided by the French space agency, the Center National d’Etudes Spatiales, the instrument is so sensitive that it can detect seismic waves thousands of kilometers away. But the September 5, 2021 event marks the first time an impact has been confirmed as the cause of such waves.
The InSight team suspects other impacts may have been masked by wind noise or seasonal changes in the atmosphere. But now that the distinctive seismic signature of an impact on Mars has been uncovered, scientists expect to find more hiding places in InSight’s nearly four years of data.
The sound of a meteoroid hitting Mars – created from data recorded by NASA’s InSight lander – sounds like a “bloop” due to a particular atmospheric effect. In this audio clip, the sound can be heard three times: when the meteoroid enters the Martian atmosphere, explodes into pieces and impacts the surface. Credit: NASA/JPL-Caltech/CNES/IPGP
The Science Behind Strikes
The seismic data offers various clues that will help researchers better understand the Red Planet. Most earthquakes are caused by underground rocks cracking due to heat and pressure. Studying how the resulting seismic waves change as they travel through different materials provides scientists with a way to study the crust, mantle, and core of Mars.
The four meteoroid impacts confirmed so far have produced small earthquakes of magnitude no greater than 2.0. These smaller earthquakes only provide scientists with a glimpse of the Martian crust, while seismic signals from larger earthquakes, such as the magnitude 5 event in May 2022, can also reveal details about the mantle and core of the planet.
But the impacts will be key to refining the Mars timeline. “Impacts are the clocks of the solar system,” says the paper’s lead author, Raphael Garcia of the Institut Supérieur de l’Aéronautique et de l’Espace. “We need to know the impact rate today to estimate the age of the different surfaces.”
Scientists 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 how often they see impacts occurring now, scientists can then estimate how many additional impacts occurred earlier in the solar system’s history.
Data from InSight, combined with orbital images, can be used to reconstruct a meteoroid’s path and the size of its shock wave. Each meteoroid creates a shock wave when it hits the atmosphere and an explosion when it hits the ground. These events send sound waves into the atmosphere. The larger the explosion, the more that sound wave tilts the ground when it hits InSight. The lander’s seismometer is sensitive enough to measure the tilt of the ground from such an event and in which direction.
“We’re learning more about the impact process itself,” says Garcia. “We can now match different sizes of craters to specific seismic and acoustic waves.”
The lander still has time to study Mars. The buildup of dust on the lander’s solar panels reduces its power and will eventually cause the spacecraft to shut down. Predicting precisely when is difficult, but based on the latest power readings, engineers now believe the lander could shut down between October this year and January 2023.
Featured Image: 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 color-enhanced image highlights dust and ground disturbed by the impact in blue to make details more visible to the human eye.
Credits: NASA/JPL-Caltech/University of Arizona