Searching for origins on the red planet

Researchers have identified the precise locations where most of the approximately 200 Martian meteorites came from. They located the meteorites in five impact craters in two volcanic regions of the Red Planet, called Tharsis and Elysium. Their study was recently published in the journal Scientific progress.

Martian meteorites find their way to Earth when an object strikes the surface of Mars with enough force that the material is “thrown off the surface and accelerated fast enough to escape Mars’ gravity,” says Chris Herd, curator of the University of Alberta’s meteorite collection and professor in the Faculty of Science. This ejected material is launched into space, orbits the sun, and some of it eventually falls back to our planet as meteorites. The explosion leaves an impact crater on the surface of Mars. This has happened 10 times in recent Martian history.

“We think we’ve found the source craters for half of the 10 groups of Martian meteorites,” Herd says.

He said scientists’ better understanding of the physics of how rocks are ejected from Mars was key to the discovery. The results of this study are a step toward unraveling the mysteries of Mars, as previous attempts to determine the precise sources of Martian meteorites have met with limited success.

“We can now group these meteorites based on their shared history and then their location on the surface before coming to Earth,” Herd says.

A better understanding of how these meteorites were formed and where they came from on Mars gives us a more detailed look at the samples we already have on Earth. The ability to contextualize and position these samples within Martian geology for the first time “will allow us to recalibrate the Martian chronology, with implications for the timing, duration, and nature of a wide range of major events in Martian history.”

“One of the major advances is being able to model the ejection process and, from that process, be able to determine the size or range of sizes of craters that could have ejected this particular group of meteorites, or even this particular meteorite,” Herd says. “I call that the missing link: being able to say, for example, that the conditions under which this meteorite was ejected were met by an impact event that produced craters that were 10 to 30 kilometers across.”

Knowledge about the origin of meteorites, combined with technological advances like remote sensing, gives researchers a framework to build on. Herd says we can also narrow down potential locations on Mars that are the source of meteorites we haven’t studied yet. “To do that, we’ll need some details about when and how a meteorite was thrown from Mars and how old it was when it crystallized on the surface of Mars,” Herd says.

“This allows us to say that, out of all these potential craters, we can narrow them down to 15, and then from those 15 we can narrow them down even further based on the specific characteristics of the meteorites.”

“We could even reconstruct the volcanic stratigraphy, which is where all these rocks were before they were ripped off the surface.” Stratigraphy is the geological record of a planet, made up of layers of sedimentary rocks or, as in this case, volcanic rocks. Think of it like a book, where the layers of rock are the pages, and from which scientists can look for clues about the planet’s past environments.

“It’s really amazing when you think about it,” Herd said. “It’s the closest thing we’re going to get to going to Mars and getting a rock back.”

As for how we can confirm that a meteorite sample found on Earth actually came from Mars, Herd explains that in the 1980s, scientists discovered that there is “a signature, a fingerprint of the Martian atmosphere, that is trapped inside these rocks.” This fingerprint includes a specific combination of gases trapped in the rock that match the gases in the Martian atmosphere measured by the Viking landers in the 1970s.

Once this framework is established, more discoveries are likely to come, as the study includes several craters in which no known Martian meteorites have been identified. While this could be because they didn’t eject any material, Herd says there’s also a real possibility that the meteorites from these particular ejections haven’t yet arrived on Earth, or haven’t yet been found.

“The idea of ​​taking a group of meteorites that were all ejected at the same time and studying them in a targeted way to determine where they were before they were ejected is an exciting step for me,” Herd says. “It’s going to fundamentally change the way we study Martian meteorites.”