The Mars lander’s seismometer has picked up vibrations from four separate impacts in the past two years, which is the first of its kind to have recorded seismic and acoustic waves from an impact on the Red Planet.
NASA’s InSight lander has detected seismic waves from four space rocks that crashed on Mars in 2020 and 2021, detected by the spacecraft’s seismometer since its landing in 2018.
A new paper published Monday in Nature Geoscience details the impacts, which 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 used for space rocks before they hit the ground – made the most dramatic entrance: It entered Mars’ atmosphere on Sept. 5, 2021, exploding into at least three shards that each left a crater behind.
Credit: NASA/JPL-Caltech
Then, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site and confirmed the location using its black-and-white Context Camera to find three darkened spots on the surface. After locating these spots, the orbiter used the High-Resolution Imaging Science Experiment camera, or HiRISE, to get a color close-up of the craters.
“After three years of InSight waiting to detect an impact, those craters looked beautiful,” said Ingrid Daubar of Brown University, a co-author of the paper and a specialist in Mars impacts. Finally, scientists confirmed three other impacts had occurred on May 27, 2020; Feb. 18, 2021; and Aug. 31, 2021.
Researchers have puzzled over why they haven’t detected more meteoroid impacts on Mars. The Red Planet is next to the solar system’s main asteroid belt, which provides an ample supply of space rocks to scar the planet’s surface. Because Mars’ atmosphere is just 1% as thick as Earth’s, more meteoroids pass through it without disintegrating.
InSight’s seismometer has also detected over 1,300 marsquakes. Provided by France’s space agency, the Centre National d’Études Spatiales, 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 noise from wind or by 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.
Listen to a Meteoroid Hitting the Red Planet
The sound of a meteoroid striking Mars – created from data recorded by NASA’s InSight lander – is like a “bloop” due to a peculiar 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.
The four meteoroid impacts confirmed so far produced small quakes with a magnitude of no more than 2.0. Those smaller 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.
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 more impacts happened earlier in the solar system’s history.
InSight’s data, in combination with orbital images, can be used to rebuild a meteoroid’s trajectory and the size of its shock wave. Every meteoroid creates a shock wave as it hits the atmosphere and an explosion as it hits the ground. These events send sound waves through the atmosphere. The bigger the explosion, the more this sound wave tilts the ground when it reaches InSight. The lander’s seismometer is sensitive enough to measure how much the ground tilts from such an event and in what direction.
The lander still has time to study Mars. Dust buildup on the lander’s solar panels is reducing its power and will eventually lead to the spacecraft shutting down. Predicting precisely when is difficult, but based on the latest power readings, engineers now believe the lander could shut down between October of this year and January 2023.
