We probably underestimated how long it took for Mars to be formed

Meteorites betray that the formation of Mars took much more time than expected.

The very young solar system was probably a violent and chaotic place. Objects such as planetesimals – building blocks of planets with a diameter of up to 2000 kilometers – were hurled through the universe, where they collided with other celestial bodies, such as Mars. In a new study published in the prestigious scientific journal Science Advances , researchers have studied these ancient clashes and come to a striking conclusion: the formation of Mars probably took much longer than scientists had thought so far.

Meteorites
An important issue in planetary science is how Mars originated and to what extent its early evolution was influenced by collisions. However, this is not an easy question. Through the test of time, most traces of this type of early impact on the red planet have long been erased. Fortunately, part of the evolution of Mars is recorded in meteorites. Of the 61,000 meteorites found to date on Earth, researchers think about 600 are from the red planet.

Elements
The researchers decided to study these Martian meteorites in the study. And thereby they come to a striking finding. The meteorites show large variations in the so-called iron-loving elements, such as tungsten and platinum. While the planet is forming, these elements are drawn to the central iron core as a kind of magnet. Nevertheless, the researchers found tungsten and platinum in the meteorites. And that means that Mars was still bombarded with planetesimals when the formation of the nucleus was already completed.

Formation
Based on earlier studies on Martian meteorites, it has been claimed that Mars formed relatively quickly; approximately in two to four million years after the birth of the solar system. But that now appears to be a somewhat premature conclusion. Large collisions may have tinkered with the isopotic balance of tungsten, which gives a distorted picture of the formation of Mars. The current research shows that it could have taken around 20 million years before Mars was ‘finished’. “Impacts of objects that have their own core and mantle can result in a heterogeneous mixture of materials in the early Mars mantle,” explains researcher Robin Canup. “This can lead to different interpretations about the time scale of the formation of Mars.”

Computer simulation of the young planet Mars. Impacts of planetesimals resulted in a heterogeneous mixture of materials in the early Mars mantle. Image: Courtesy of Southwest Research Institute

The meteorites that have landed on Earth are probably from only a few places on the red planet. And so we actually have too few meteorites available to give a good indication of how long it took for Mars to form. The researchers are already looking forward to the next Mars missions to solve the mystery. “To get a full grip on Mars, we need to understand the role that the very first impacts played in its evolution and composition,” concludes research leader Simone Marchi. We probably don’t have to wait that long for that. For example, four space missions to Mars are already planned this year. During the expeditions, samples will also be collected which will then be brought to Earth for further analysis.

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