The Seismic Experiment for Internal Structure (SEIS) seismometer on NASA’s InSight lander picked up vibrations and sounds from four space rocks that crashed on Mars in 2020 and 2021; orbital imaging from NASA’s Mars Reconnaissance Orbiter provided ground truth for these seismic sources.
These craters were formed by a meteoroid impact on Mars on September 5, 2021, the first to be detected by NASA’s InSight lander; 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. Image credit: NASA / JPL-Caltech / University of Arizona.
The atmospheric entry and surface collision of a meteoroid at high speeds generates shock waves.
These decay into seismic and acoustic waves that can be detected by seismometers.
Such waves have been recorded for airburst events — where the impactor breaks up before reaching the surface — in Earth’s atmosphere, and for the formation of a single small impact crater on Earth.
However, geophysical observations of new crater formation on other planets have been limited.
“Impacts are the clocks of the Solar System. We need to know the impact rate today to estimate the age of different surfaces,” said Dr. Raphael Garcia, a researcher at the Institut Supérieur de l’Aéronautique et de l’Espace.
Dr. Garcia and his colleagues analyzed the data from InSight’s SEIS instrument and identified seismic and acoustic waves from four meteoroid impacts.
Designated S0533a, S0793a, S0981c and S0986c, these impacts produced small quakes with a magnitude of no more than 2.0 and ranged between 85 and 290 km (53-180 miles) from InSight’s location in the Elysium Planitia region.
The first of the four confirmed meteoroids, S0986c, made the most dramatic entrance: it entered the Martian atmosphere on September 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 researchers used the HiRISE camera on the orbiter to get a color close-up of the craters.
“After three years of InSight waiting to detect an impact, those craters looked beautiful,” said Dr. Ingrid Daubar, a researcher at Brown University.
After combing through earlier SEIS data, the scientists confirmed three other impacts had occurred on May 27, 2020; February 18, 2021; and August 31, 2021.
“With identified seismic sources, the seismic waves can be used to constrain the structure of the Martian interior, corroborating previous crustal structure models, and constrain scaling relationships between the distance and amplitude of impact-generated seismic waves on Mars, supporting a link between the seismic moment of impacts and the vertical impactor momentum,” they said.
“Our findings demonstrate the capability of planetary seismology to identify impact-generated seismic sources and constrain both impact processes and planetary interiors.”
The findings were published in the journal Nature Geoscience.
R.F. Garcia et al. Newly formed craters on Mars located using seismic and acoustic wave data from InSight. Nat. Geosci, published online September 19, 2022; doi: 10.1038/s41561-022-01014-0
Source : Breaking Science News