The uranium-containing mineral zircon is a rich component of the Earth’s continental crust, providing information about the continent’s age and origin, as well as huge geological features such as mountain ranges and massive volcanoes. However, unlike Earth, Mars’ crust has not evolved, and zircons are constructively similar to the crust found under the rare Earth’s oceans. Therefore, zircon is not expected to be a common mineral on Mars.
“When we found so many zircons in this Mars meteorite, we were very surprised and excited. Zircons are incredible durable crystals that can date and preserve information that tells us about their origins. Too much zircons. Approaching to is like opening a window of time, explains Professor Martin Bizzarro of the GLOBE Institute who led the study.
The research team investigated an ancient Mars meteorite NWA 7533 (Figure 1) named “Black Beauty” discovered in the Moroccan desert in 2011. After crushing 15 grams of this rock, they extracted about 60 zircons. By dating zircons, they found that most decisions date back about 4.5 billion years, that is, the beginning of planetary life. But they also made some unexpected discoveries. Some zircons have defined a much younger age, ranging from about 150 million to 300 million years.
“This young age was a big surprise,” says Bizzarro. “The Black Beauty meteorite is believed to have come from the southern hemisphere of Mars, which has no young volcanic terrain. The only source of this young zircon is the Tharsis volcanic region, located in the planet’s northern hemisphere. It is a recently active volcano,” adds Martin Bizzarro.
Mars’ Tharsis overhang is a massive volcanic area with the largest volcano in the solar system up to 21 km high. Scientists believe that this volcanic region is an expression of very deep magmatism erupting from the planet’s surface. The Earth’s analogy is a chain of Hawaiian volcanic islands, believed to reflect volcanic activity that lies deep. However, due to plate tectonics, the Pacific plate is constantly moving to form a chain of younger volcanic islands instead of accumulating in one location. Since Mars does not have plate tectonics, volcanoes accumulate in one place, resulting in a huge size.
If Bizzarro’s team is right, it means that young zircons could contain information about Mars’ deep and inaccessible interiors. This is the first time that scientists have direct access to the deep interior of the Red Planet, which can reveal Mars’ internal structure and composition through this sample.
“It’s important to have a deep internal sample of Mars. This means we can now use this zircon to investigate the origin of volatile elements, including water on Mars, and see how it compares to Earth and other planets in our solar system.” Mafalda Costa explains.
However, to understand the properties inside deep Mars, the researchers turned to an analysis of the isotopic composition of the element hafnium in the same zircon.
“Hafnium is the main elemental component of zircon, so it maintains a memory of where the zircon was formed,” says Martin Bizzarro. “We found that the young zircon’s hafnium isotope composition is different from the known Martian meteorites, indicating that the young zircons came from primitive reservoirs that didn’t know existed inside Mars,” he adds.
The hafnium isotope composition of young zircons resembles the most primitive objects in the solar system, namely chondrite meteorites. This chondrite meteorite is a sample that has never been modified since the asteroid was created. This means that the deep interior of Mars has not been modified in nature since the formation of the planet (Fig. 2). The presence of such primitive reservoirs is expected for planets without plate tectonics. Unlike Earth, in which the material formed on the surface is continuously recycled inside by plate tectonics, the deep interior of Mars has not changed since the planet was born, and thus preserves its initial composition.
Finally, the discovery that the surface of Mars may be rich in zircons could guide future planetary robotic exploration, especially in the framework of returning samples to Earth.
Martin Bizzarro concluded, “Our research makes it clear that the return mission aimed at obtaining zircon-containing samples will have high scientific value in understanding Mars’ geological history.”
The research was supported by the Carlsberg Foundation, the Danish National Research Foundation and the European Research Council.
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