NASA’s InSight lander has detected seismic waves from four space rocks that crashed on Mars in 2020 and 2021. Not only do these represent the first impacts detected by the spacecraft’s seismometer since InSight touched down on the Red Planet in 2018, it also marks 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 85km and 290km 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.
Then, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site to confirm the location. The orbiter used its black-and-white Context Camera to reveal three darkened spots on the surface. After locating these spots, the orbiter’s team used the High-Resolution Imaging Science Experiment camera, or HiRISE, to get a color close-up of the craters (the meteoroid could have left additional craters in the surface, but they would be too small to see in HiRISE’s images).
“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.
This collage shows three other meteoroid impacts that were detected by the seismometer on NASA’s InSight lander and captured by the agency’s Mars Reconnaissance Orbiter using its HiRISE camera.
Credits: NASA/JPL-Caltech/University of Arizona
After combing through earlier data, 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 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.
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. Credit: NASA/JPL-Caltech/CNES/IPGP
Science behind the strikes
Seismic data offer various clues that will help researchers better understand the Red Planet. Most marsquakes are caused by subsurface rocks cracking from heat and pressure. Studying how the resulting seismic waves change as they move through different material provides scientists a way to study Mars’ crust, mantle, and core.
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.
But the impacts will be critical to refining Mars’ timeline. “Impacts are the clocks of the solar system,” says the paper’s lead author, Raphael Garcia of Institut Supérieur de l’Aéronautique et de l’Espace. “We need to know the impact rate today to estimate the age of 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 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.
“We’re learning more about the impact process itself,” Garcia says. “We can match different sizes of craters to specific seismic and acoustic waves now.”
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.
Featured picture: These craters were formed by a Sept. 5, 2021, meteoroid impact on Mars, the first to be detected by NASA’s InSight. Taken by NASA’s Mars Reconnaissance Orbiter, this enhanced-color image highlights the dust and soil disturbed by the impact in blue in order to make details more visible to the human eye.
Credits: NASA/JPL-Caltech/University of Arizona