Tracing Martian meteorites to the largest volcanic structure in the solar system

About a million years ago, an asteroid collided with the smooth surface of Mars. The collision released a cloud of debris and some of the rocky debris was dropped into the atmosphere, escaping the planet’s gravity to travel through the darkness of space.

Some of these rocks eventually found their way to Earth and survived diving through our planet’s atmosphere to crash to the surface – including a portion of seven pounds that crashed in Morocco in 2011. Now known to scientists as the “depleted chergotite,” this group of more than a dozen space rocks makes up an intriguing part of the 317 Mars meteorites That there is knowledge on our planet – the only Martian substance on Earth.

Determining the region of Mars where these meteorites came from is an integral part of unraveling the planet’s history, but it is proving to be a major scientific challenge. Now, with the help of crater-counting machine-learning software, a team of researchers studying depleted shergotite may have finally solved the case: the team concluded that these geologic ejections came from a particular crater, on top of Tharsis, the largest volcanic province. in the solar system.

This ancient volcanic giant on Mars is dotted with thousands of individual volcanoes and spans an A . scale Area Three times the continental area of ​​the United States. The volcano was formed over billions of years by countless injections of magma and lava flows – so heavy that as it formed, it effectively rotated the planet in 20 degrees.

If the meteorites actually come from Tharsis, the analysis also published in Nature CommunicationsSo, scientists have meteorites that could help identify the infernal forces that fueled the construction of a volcano capable of tilting worlds.

“This could really change the paradigm of how we understand Mars,” he says. Luke Daly, who specializes in meteorites at the University of Glasgow, was not involved in the study.

meteorite tracks

Most Martian meteorites fall into a class called shergottites, named after the Indian city of Sherghati, where meteor Falling from the sky in 1865. Shergotite are all volcanic rocks with similar compositions, but some, the poor chergotite, have a strange chemical signature.

On Mars, some elements like neodymium and lanthanum do not bind well to the minerals in the mantle, the solid but fungal part of the planet that lies beneath the crust. Poor chergotite lacks these elements – hence the name “poor” – suggesting that they came from the mantle of Mars.

So how did these rocks get so close to the planet’s surface that they were dropped in the event of an impact? On Earth, mantle rock can reach the surface in two ways: when two tectonic plates move apart and allow the mantle to emerge, or when a source of superheated mantle material, known as a plume, emerges from the depths. Apparently, Mars has never had plate tectonics, so a mantle plume is the most likely scenario.

Scientists also know that all the rocks came from a relatively small volcanic site – possibly a mound of lava flow deposits – based on radioactive decay From specific elements to us meteorites.

If all of these volcanic rocks were the result of a single collision, it must have been a very powerful collision, opening a crater at least three kilometers in diameter and possibly much larger. And the crater must be about 1.1 million years old, as the cosmic rays that bombarded and altered the surfaces of the meteorites reveal how long they traveled through space after the collision.

Despite all these clues, tracing these bits of Martian rock back to their place of origin was very difficult. It’s like the individual pieces of a puzzle that are separated from all the others – and without knowing what their original environment looked like, it’s nearly impossible to fit them into a particular part of the planet.

“As geologists, we log a lot of information about where we collect rock samples from, because context is important,” says Shane O’Brien, a doctoral student who studies Martian meteorites at the University of Glasgow. “In the case of Martian meteorites, since we don’t know the context, we need a well-founded assessment of what happened to form them.”

To make this assessment, the scientists used a new tool in planetary science: machine learning.

A pit among the millions

The only way to definitively determine the age of the planet’s surface is through a physical sample and study its radioactive compounds. But even NASA and the campaign Mars sample return From the European Space Agency to returning some pure Martian rock to Earth in the 1930s, researchers are relying on a technique known as crater counting to estimate the age of surfaces.

On Earth, strong winds, flowing water, erupting lava, and an abundance of living creatures rapidly eroded ancient archaeological craters. It’s different on Mars because it’s a geologist in a coma, with light winds and no surface water. On the Red Planet, large craters remain intact for hundreds or even billions of years. Assuming the rate of impacts over time is known, a surface on Mars with more craters may be older than a surface with fewer craters.

Scientists can use other alternatives to infer the age of the hole. “When an asteroid hits the surface, there’s a lot of debris being ejected,” he says. Anthony LagenD., a planetary geologist at Curtin University and lead author of the new study. Pieces that land on Mars impact the surface and form small secondary craters around the original crater. Even on Mars, these tiny craters suffer from wind erosion over millions of years, so any massive crater surrounded by tiny craters must have occurred recently in the planet’s history.

“To better understand the ages, we need to identify the smallest pits,” he says. Gretchen Benedix, an astronomy specialist at Curtin University and co-author of the study. Smaller impacts are more common than larger impacts, so we can use small differences in the number of smaller craters on two surfaces to calculate more detailed timelines.

To find out if one of the craters was exactly 1.1 million years old, the team needed to catalog the tiny craters on Mars and use them to accurately date the planet’s surface. This process, if performed manually, would be torture. Instead, the researchers put orbital images of Mars into machine learning software and trained the system to find craters 500 meters in length.

He said the program quickly discovered about 90 million holes. Costa . ServiceCurtin University data scientist and co-author of the study. With this pit schedule, the team can begin to narrow down the potential origins of depleted chergotite.

fragments of a volcanic giant

After examining the data, the team identified 19 large craters in volcanic regions of Mars that were surrounded by many secondary craters – a sign that these planetary scars could be as small as the 1.1 million-year-old crater they were looking for. By cataloging 90 million small craters, researchers have been able to accurately date the layers of debris radiating from the larger craters, revealing more accurate estimates of their ages.

Some of the pits were about the right age, but more was needed. The age of formation of the surrounding terrain must also match the age of the minerals in the meteorites. To verify this, the team again used the crater catalog to date the volcanic plains.

Of the 19 large craters, only two were small volcanic deposits excavated by a collision event 1.1 million years ago: crater 09-00015 and crater 09-00015. critera toning. The latter (named after an area in London) appears to have formed due to a strong tilting impact – the type of collision that would send many meteorites into space.

“The Totting crater has a special type of sediment of material that was ejected in several layers, indicating that there was ice or water nearby at the time of impact,” he says. Peter Grindrud, a planetary scientist at the Natural History Museum in London, who was not involved in the study. Impact simulations show that ice and water can generate more debris, much of which, if pushed enough, could escape into space.

With all this evidence, the team identified Tooting crater, which is 30 kilometers long, as the prime suspect in the origin of the depleted shergotite. “It’s a well-crafted argument,” says Luke Daly. “Everything seems to fit.”

Scientists haven’t completely ruled out crater 09-00015, but the important thing is that both craters “are located in the Tharsis region, where a vast hot spot, or super plume, is thought to have produced this massive bulge on Mars.” Peter Grindrud says. No matter what crater the meteorites came from, both can learn more about the story of the largest volcanic region on Mars.

The crater census has already revealed that some of the features of Tharsis were made more than 3.7 billion years ago, but meteorites on Earth are only a few hundred million years old. This indicates that the Tharsis super plume is roughly as old as the Red Planet itself, and that it continued to produce magma long after many of the planet’s other volcanic centers had disappeared.

Like the earth pillarsMars’ mantle plumes helped shape the evolution of the planet’s surface, with massive eruptions of gases that altered the atmosphere while dramatically altering the planet’s topography. Tharsis’ super plume may have had a near-continuous influence on the evolution of the Red Planet.

Gone are the times of frequent volcanic eruptions on Mars, but the prolonged volcanoes of Tharsis reinforce the idea that even the smallest planets, which should have lost their internal heat eons ago, can survive volcanically active Much longer than previously thought

Deciphering the craters of other worlds

Driven by the discovery, Anthony Lagne’s team hopes to identify craters that originated from other Martian meteorites, including some ancient, that could reveal more about the past. full of water Mars.

However, the implications of this study depend on the correct performance of the machine learning program in hole counting. Crater counting is fraught with difficulties: the rate of impacts over time, for example, is estimated, and the tiny circular structures on Mars that resemble craters can fool a computer program.

“Machine learning is really a creative way to try to solve this problem,” he says. Lauren Joswiak, a planetary volcanologist at the Johns Hopkins University Applied Physics Laboratory, who was not involved in the study. “I hope this method works because if it does, it will be very interesting to try to apply it to other planets.”

The study authors agree. “Mars is wonderful,” Gretchen Benedix says. But this algorithm and methodology is not only applicable to Mars. We can use it on the moon or on Mercury.”

If machine learning does indeed solve this long-standing mystery about meteorites, it opens the door to all kinds of possibilities we never dreamed of. “Without a doubt, we are just beginning to see the implications of machine learning on planetary science,” says Peter Grindrud.

This article was published in English on Location nationalgeographic.com