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Believe it or not, debris from Mars frequently reaches Earth after powerful impacts hit the Red Planet’s surface and hurl it into space.
There have been at least 10 of these meteorite-forming events in Mars’ recent history. When these large impacts occur, meteorites are ejected from the Red Planet fast enough that they escape Mars’ gravity and enter orbit around the Sun, with some eventually falling to Earth.
Scientists at the University of Alberta have traced the origins of 200 of these meteorites to five impact craters in two volcanic regions on Mars known as Tharsis and Elysium. “We can now group these meteorites based on their common history and then their location on the surface before they arrived on Earth,” said Chris Herd, a professor in the faculty of science and curator of the university’s meteorite collection. expression.
Meteorites fall to Earth all the time — an estimated 48.5 tons (44,000 kilograms) of meteorite material falls each day, according to NASA — but the majority reach the surface as small, unnoticeable dust particles. Their origin can often be difficult to determine, but in the 1980s, scientists began to suspect a group of meteors that appeared to be of volcanic origin and were 1.3 billion years old.
This meant that these rocks must have come from a body that had recently experienced volcanic activity (in geological terms), making Mars a likely candidate. However, evidence emerged when NASA’s Viking landers were able to compare the composition of the Martian atmosphere to the trapped gases in these rocks.
It has previously been difficult to determine exactly where on Mars they originated. The team notes in their paper that this difficulty was due to the use of a technique called spectral matching, which is used to identify and compare the composition of materials by analyzing light patterns.
But this method is limited by factors like terrain variability and extensive dust cover, which can skew spectral signals, especially in younger terrains like Tharsis and Elysium. But knowing exactly where these Martian meteorites came from allows scientists to better piece together the planet’s geological history.
“[It would] “It makes it possible to recalibrate the chronology of Mars and make inferences for the timing, duration and nature of a wide range of important events in Martian history,” Herd said. “I call this the missing link – being able to say, for example, that the conditions under which this meteorite was ejected coincided with an impact event that produced craters 10 to 30 kilometers in diameter.”
The team combined high-resolution simulations of impacts on a Mars-like planet. “One of the big advances here is being able to model the ejection process and from that process be able to determine the crater size, or range of crater sizes, that could have ultimately ejected that particular group of meteors or even that particular meteor,” Herd said.
The model’s output allowed the team to determine the “peak shock pressures” of impact events and the length of time rocks were exposed to those pressures. This can be determined from “shock features” observed in meteorites; for example, unique mineral alterations, impact glass, and specific fracture patterns.
From this data, Herd and his colleagues were able to estimate the size of the impact craters that might have ejected the meteors and how deep the rocks were buried before the impact. While these depth estimates contain some uncertainty, the researchers compared them to the local geology of the possible source craters and the characteristics and ages of the meteors to see if they matched up.
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“[Our modelling approach] “That allows us to say that out of all these potential craters, we can narrow it down to 15, and then from 15 we can narrow it down even further based on certain meteorite features,” he said. “Maybe we can reconstruct the volcanic stratigraphy [the geological record]”, the position of all these rocks before they broke away from the surface.”
This could help scientists better understand when volcanic events on Mars occurred, the different sources of Martian magma and how quickly craters formed during a period of low meteor bombardment on the Red Planet known as the Amazonian period about 3 billion years ago.
“It’s really incredible if you think about it,” Herd added. “This is the closest we’ve ever come to going to Mars and getting a piece of rock.”