Elusive Internal Structure of Mars Revealed by Ancient Zircon Minerals From the Red Planet

Analysis of an ancient meteorite from Mars suggests that the mineral zircon may be abundant on the surface of the red planet.

By determining the age and hafnium isotope composition of zircons, researchers from the University of Copenhagen have shown that a population of these crystals were sourced from the deep interior of Mars. If the researchers are correct, it means that the young zircons contain information about the deep, inaccessible interior of Mars, which provides insights into the internal structure of the planet.

“Zircon are incredibly durable crystals that can be dated and preserve information that tell us about their origins. Having access to so many zircons is like opening a time window into the geologic history of the planet.” — Professor Martin Bizzarro

The uranium-bearing mineral zircon is an abundant constituent of Earth’s continental crust, providing information about the age and origin of the continents and large geological features such as mountain chains and giant volcanoes. But unlike Earth, Mars’s crust is not evolved and is compositionally similar to the crust found under the Earth’s oceans, where zircon is rare. Therefore, zircon is not expected to be a common mineral on Mars.

“We were quite surprised and excited when we found so many zircons in this Martian meteorite. Zircon are incredibly durable crystals that can be dated and preserve information that tell us about their origins. Having access to so many zircons is like opening a time window into the geologic history of the planet,” describes Professor Martin Bizzarro from the GLOBE Institute, who led the study.

The team investigated the ancient Martian meteorite NWA 7533 (Figure 1), dubbed “Black Beauty,” which was discovered in the desert of Morocco in 2011. After crushing 15 grams of this rock, they extracted about 60 zircons. By age-dating the zircons, they found that the majority of crystals date back to about 4.5 billion years ago, namely the very beginning of the planet’s life. But they also made an unexpected discovery: some zircons defined much younger ages, ranging from about 1500 million years down to 300 million years.

Figure 1: The NWA 7533 zircon-rich meteorite containing fragments of the ancient crust of Mars. Credit: © University of Copenhagen/Deng et al.

“These young ages were a great surprise,” says Bizzarro. “The Black Beauty meteorite is believed to come from the southern hemisphere of Mars, which does not have any young volcanic terrains. The only possible source for these young zircons is the Tharsis volcanic province located in the northern hemisphere of the planet, which contains large volcanoes that were recently active,” Martin Bizzarro adds.

The Tharsis bulge on Mars is an enormous volcanic province that hosts the largest volcanoes in the Solar System, which are up to 21 km high. Scientists believe that this volcanic province is the expression of very deep magmatism that erupts on the planet´s surface. The analogy on Earth is the Hawaiian volcanic chain of islands, which is also believed to reflect deep-seated volcanic activity. But because of plate tectonics, the Pacific Plate is constantly moving such that, instead of accumulating at one single location, a chain of progressively younger volcanic islands has formed. Since Mars does not have plate tectonics, the volcanoes pile up at one single location and as a result grow to gigantic sizes.

“Having samples of the deep interior of Mars is key. This means that we can now use these zircons to probe the origin of the volatile elements on Mars, including its water, and see how it compares with Earth and other planets in the Solar System.” — Mafalda Costa

If Bizzarro’s team is correct, it means that the young zircons may contain information about the deep, inaccessible interior of Mars. This is the first time that scientists have direct access to the deep interior of the red planet via these samples, which may allow them to uncover the internal structure and composition of Mars.

“Having samples of the deep interior of Mars is key. This means that we can now use these zircons to probe the origin of the volatile elements on Mars, including its water, and see how it compares with Earth and other planets in the Solar System,” explains Mafalda Costa, first other of the new study.

But to understand the nature of the deep Martian interior, the researchers turned to the analysis of the isotopic composition of the element hafnium in the same zircons.

“Because hafnium is a major elemental constituent of zircon, it retains a memory of where the zircon formed,” says Martin Bizzarro. “We found that the hafnium isotope composition of the young zircons is unlike any of the known Martian meteorites, which indicates that the young zircons come from a primitive reservoir that we did not know existed in the interior of Mars,” he adds.

Figure 2: Unravelling the internal structure of Mars. An upwelling plume of primitive material rises from the deep mantle, feeding a volcanoes at the planet’s surface. Credit: University of Copenhagen

The hafnium isotope composition of the young zircons is similar to the most primitive objects in the Solar System, that is chondrite meteorites. These chondrite meteorites are samples of asteroids that have never been modified since their formation. This implies that the deep interior of Mars has essentially not been modified since the formation of the planet (Figure 2). The existence of such a primitive reservoir is ex meteorites are samples of asteroids that have never been modified since their formation. This implies that the deep interior of Mars has essentially not been modified since the formation of the planet (Figure 2). The existence of such a primitive reservoir is expected for a planet lacking plate tectonics. In contrast to Earth, where material formed at surface is continuously recycled into the interior by plate tectonics, the deep interior of Mars has remained unchanged since the birth of the planet and, as such, preserves its initial composition.

Finally, the discovery that zircon may be abundant on the Martian surface may guide the future robotic exploration of the planet, especially in the framework of returning samples to Earth.

“Our study makes clear that a return mission targeted at acquiring zircon-bearing samples will be of high scientific value towards understanding the geologic history of Mars,” concludes Martin Bizzarro.

Reference: “The internal structure and geodynamics of Mars inferred from a 4.2 Gyr zircon record” by Maria M. Costa, Ninna K. Jensen, Laura C. Bouvier, James N. Connelly, Takashi Mikouchi, Matthew S. A. Horstwood, Jussi-Petteri Suuronen, Frédéric Moynier, Zhengbin Deng, Arnaud Agranier, Laure A. J. Martin, Tim E. Johnson, Alexander A. Nemchin and Martin Bizzarro, 16 November 2020, Proceedings of the National Academy of Sciences of the United States of America.
DOI: 10.1073/pnas.2016326117

The study was supported by the Carlsberg Foundation, the Danish National Research Foundation and European Research Council.

GeologyGeophysicsMarsUniversity of Copenhagen
Comments ( 9 )
Add Comment
  • Louis Peloquin

    How do they know for sure that the NWA 7533 meteorite found in the Morocco desert comes from Mars?

    • Torbjörn Larsson

      Good question!

      Sufficiently large meteorites have thin “fusion crusts” from traveling the atmosphere while braking from it, so they stand out on fields in deserts and on ice (popular to look in Antarctica, where the ice flows to some mountains and thaw out so concentrating the rocks).

      “These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmospheric gases on Mars, which have been measured by orbiting spacecraft, surface landers and rovers.[3][4]” [“Martian meteorite” @ Wikipedia]

  • Louis Peloquin

    How do they know for sure that the NWA 7533 meteorite comes from Mars?

  • Louis Peloquin

    Seems that this other article, is referring to some form of correlation with samples by Curiosity Rover, to deduct in the first place, the Martian origin of certain meteorites found on Earth:
    “Using Martian Meteorites to Reconstruct Mars’ Chaotic History”

  • Torbjörn Larsson

    This happenstance find is very telling on Mars! Besides explaining earlier finds of different mantle sources of volatiles – by vertical layering of crust in a global magma ocean and later untouched by global convection – it also mentions in the abstract: “Ancient zircons record ages from 4485.5 ± 2.2 Ma to 4331.0 ± 1.4 Ma, defining a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma. We interpret these to represent intense bombardment episodes at the planet’s surface, possibly triggered by the early migration of gas giant planets.”

    So they see an early bombardment rapidly tailing off, but relatively little after. This is consistent with other recent finds [“Cataclysmic bashing from giant planets occurred early in our Solar System’s history”, Science; “Vesta Samples Suggest an Older, Longer Collisional History in the Early Solar System”, Planetary News].

  • Vansh Varia

    Good to know scientist’s are good a great job on this type of discoveries hands off to space scientists

  • Kevin Buchanan

    Why not land a probe in Mars extinct volcano

  • Darkpsychomeowz

    What happens if we introduce rain to mars via “storm salts”
    Like here on earth or 🌀maybe try to plant fruit seeds on mars leave them in contained units with enough nutrient material packed down where in the patches of dirt where they are buried to last about 2 years and watered by one or two robots who are programmed to do such a routine and simply let them possibly adapt to the atmosphere though you would have to figure out oxygen and sunlight unless it’s already been done…?

  • Darkpsychomeowz

    What happens if you all plant fruit seeds in patches of dirt from earth specially packed with nutrients enough to last a year or two and have specially programmed robots water those patches with the fruit seeds in them,which would also allow for documentation of how vegetation could do on mars until further notice is uncovered.

    For reasons of avoiding problematic continental/countrywide political ties its best it be simple as fruit seeds which is something easy to keep notes on and not initially jump the board to trees and bushes yet which may end up being less productive (and possibly costing more money in the long run) then having seeds develop into their OWN plant life on an entirely different planet,this also granting some studies on the differences of growth patterns in the atmospheres when water comes into the picture on a larger scale if so.