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Hundreds of millions of years ago, something crashed into the planet Mars with enough force to eject pieces of Martian rock into space. Some of these pieces of rock made their way to Earth where they entered our atmosphere as meteors. Some precious have landed on the surface of our planet as meteorites. Thanks to scientists like Geoffrey Howarth, a geologist at the University of Cape Town (UCT), these Martian meteorites are now being studied to better understand the red planet’s structure and geological history. Here’s what we know so far.
Howarth, raised on a farm in the Eastern Cape, first stumbled upon the field of igneous petrology (the study of how volcanic rocks are formed) as a college student. He did not know then that he would someday specialize in two very different types of igneous rocks: one that formed in the heart of our planet and others that came from the surface of a planet 137 million kilometers away.
“As a child I liked collecting rocks because I found them mysterious, but only later, when I started studying geology, was I fascinated by what rocks can tell us about the history of a planet over time. I still remember the first time I came across a Martian meteorite, holding a small piece of a different planet in my hand certainly made an impression. “
Today, Howarth’s research focuses on kimberlite, the type of rock in which most diamonds are found and which forms deep in the earth’s crust, as well as the meteorites of Mars.
Cloaked messengers
To date, Howarth and a global team of geologists have studied 252 individual Martian meteorites from 11 distinct ejection sites on Mars. Some of these samples are on loan from NASA, while many more were purchased more recently in Northwest Africa from local Bedouin experts and commercial meteorite hunters.
“The study of these meteorites provides us with information on the composition, differentiation and evolution of the Martian mantle. Meteorites also offer clues to secondary geological processes such as the role water played in the formation of these rocks, ”explains Howarth.
“The Martian interior is more diverse than previously thought.”
To understand the chemical composition of meteorites Howarth and his team use an electronic probe to analyze very thin sections of the rock.
According to Howarth, the data collected so far shows that Mars has a heterogeneous mantle, which means that it is made up of a variety of different types of rocks.
“These various mantle sources didn’t mix very much because, unlike Earth, Mars doesn’t have any plate tectonics. The recent discovery of new Martian meteorites has revealed a diversity of magmatic sources and history, and that the Martian interior is more diverse than previously thought. “
A recent article published in Journal of Geophysical Research: Planets by Howarth and other geologists around the world, also explains that the study of these Martian meteorites supports the idea that early Martian history involved rapid accretion and core formation relative to Earth.
But Howarth warns that most of the Martian meteorites studied to date are quite young by geological time standards, and combined with the fact that many come from the same ejection sites on Mars, they cannot give us a complete understanding of Martian geology.
“Most of the meteorites studied so far are only about 600 million years old.”
Time capsules from space
“Most of the meteorites studied so far are less than 600 million years old. Three quarters of the meteorites are shergottites (named after the first place they were found at Sherghati in India), which are almost identical to the rocky basalt found here on earth. The rest is mainly composed of Nakhliti, named after the Nakhla meteorite found in Egypt in 1911. These too are igneous (volcanic) rocks composed largely of augite and olivine crystals. “
Over the past two decades, the number of Martian meteorites recovered has nearly doubled, which has allowed scientists to study meteorite suites for the first time. But according to Howarth, this still represents a partial sample with many from unknown ejection sites on the surface of Mars.
“To really be able to look back in time and understand how the surface and interior of Mars formed, we need samples from Mars itself. Fortunately for us, the Mars 2020 Perseverance rover aims to collect over 30 different surface samples from the Jezero Crater on Mars. These rock samples could be returned to earth as early as 2031 “.
These samples will allow scientists like Howarth to analyze a greater variety of Martian rocks with known origins.
“Studying these rocks alongside meteorites will help us narrow down our assumptions about how the Martian interior and surface evolved,” Howarth says.
Water on Mars
Howarth has a particular interest in the history of water on Mars and its role in atmospheric dynamics and volcanic activity.
Previous missions to Mars have shown strong evidence of the past presence of water on its surface, as well as the current presence of ice in the polar ice caps and underground of the planet.
Howarth explains that by studying how and when minerals in Martian meteorites interacted with water, we can better understand the hydrological history of Mars itself.
“Previous missions to Mars have shown strong evidence of the past presence of water on its surface.”
“While some of these minerals formed directly from crystallized magma, others formed through interaction with water that occurs on the Martian surface or subsoil. Thus, we know that at the beginning of the planet’s history there must have been a considerable presence of water. What we don’t know is how much the water cycle took place on Mars or how similar it could have been to our planet. “
Not in seventh heaven yet
Howarth hopes that the discovery of new Martian meteorites here on earth, or the return of samples from the next mission to Mars, will help answer some of the many remaining questions about the planet’s geology.
“Once we have access to the oldest Martian rocks, we can begin to answer questions about the role of water in Martian magmatism (magma activity), such as how the magma ocean on Mars crystallized, such as the volcanic rocks have been found on the planet’s surface and how volcanic activity on Mars has evolved over time. “
But Martian meteorites aren’t the only interstellar rock fragments Howarth is interested in.
“In the future I hope to apply these techniques to other meteorites such as the lunar meteorites from the moon. I think in many important ways Mars is indeed a starting point. Although the current COVID-19 crisis has meant that I have had to put my plans for an awareness project on hold, I hope to be able to share this work with students soon so that they too can be excited about its possibilities, just like I did. I was the first time I held a piece of Mars when I was a student. “
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