By Stephen Beech via SWNS
Mars is bombarded by around 300 basketball-sized meteorites every year, according to a study of seismic signals.
The information may provide a new “cosmic clock” tool for dating planetary surfaces, say scientists.
The study sheds new light on how often ‘marsquakes’ caused by meteorite impacts occur on the red planet.
An international research team found that Mars experiences around 280 to 360 meteorite impacts every year that produce craters larger than eight meters (26ft) in diameter and shake the surface.
The study, published in the journal Nature Astronomy, was led by scientists at Imperial College London and ETH Zurich in Switzerland, working as part of NASA’s InSight mission.
The rate of marsquakes, which were detected by InSight’s ‘seismometer’ – an instrument capable of measuring the slightest ground movements, exceeds previous estimates based on satellite images of the planet’s surface.
Scientists say the seismic data could be a better, more direct way of measuring meteorite impact rates- and could help scientists date planetary surfaces across the Solar System more accurately.
Study co-first author Dr Natalia Wojcicka, of Imperial College, said: “By using seismic data to better understand how often meteorites hit Mars and how these impacts change its surface, we can start piecing together a timeline of the red planet’s geological history and evolution.
“You could think of it as a sort of ‘cosmic clock’ to help us date Martian surfaces, and maybe, further down the line, other planets in the Solar System.”
For years, scientists have been using the number of craters on Mars and other planets’ surfaces as ‘cosmic clocks’ to estimate planetary age – with older planet surfaces pitted with more craters than younger ones.
To calculate planetary age, scientists have traditionally used models based on craters on the Moon to predict the rate of meteorite impacts of different sizes over time.
To apply the models to Mars, they need to be adjusted for how the atmosphere might stop smaller objects from hitting the surface and Mars’s different size and position in the Solar System.
For small craters less than 60 meters (197ft) wide, scientists have also been able to observe how often new craters form on Mars using satellite images. But the number of craters found that way is much lower than expected.
In the new study, researchers identified a previously unrecognized pattern of seismic signals, as produced by meteorite impacts.
The signals stood out for their unusually greater proportion of high-frequency waves compared to typical seismic signals, as well as other characteristics, and are known as ‘very high-frequency’ marsquakes.
The research team found the rate of meteoroid impacts to be higher than previously estimated by looking at freshly formed craters captured by satellite images and in agreement with extrapolating data from craters on the Moon’s surface.
The findings highlighted the limitations of previous models and estimates, as well as the need for better models to understand crater formation and meteorite impacts on Mars.
Researchers used NASA’s InSight lander and its extremely sensitive seismometer, SEIS, to record seismic events possibly caused by meteorite impacts.
SEIS detected seismic signatures characteristic of the very high-frequency marsquakes, which the team found to be indicative of meteoroid impacts and different from other seismic activity.
Using the new method for detecting impacts, researchers found many more impact events than predicted by satellite imaging, particularly for small impacts that produce craters only a few meters across.
Study co-author Professor Gareth Collins, of Imperial College, said: “The SEIS instrument has proven to be incredibly successful at detecting impacts – listening for impacts seems to be more effective than looking for them if we want to understand how often they occur.”
Dr. Wojcicka said: “To understand the inner structure of planets, we use seismology.
“This is because as seismic waves travel through or reflect off material in planets’ crust, mantle, and core, they change.
“By studying these changes, seismologists can determine what these layers are made of and how deep they are.”
She added: “On Earth, you can more easily understand the inner structure of our planet by looking at data from seismometers placed all around the globe.
“However, on Mars, there has been only one – SEIS.
“To better understand Mars’ inner structure, we need more seismometers distributed across the planet.”
The research team is also involved in another study, published in the journal Science Advances, which used images and atmospheric signals recorded by InSight to estimate how often impacts occur on Mars.
Despite using different methods, both studies reached similar conclusions, strengthening the overall findings.
