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Mars took way longer to form than we thought, ancient impacts reveal

Scientists believe early cosmic impacts may have influenced the evolution of Mars, and this suggests that the Red Planet formed much slower than previously thought. 

The early solar system was a violent, chaotic place, where planetesimals — small protoplanets measuring up to 1,200 miles (1,900 kilometers) in diameter — asteroids and other debris collided, shaping the planets and celestial bodies we know today. 

A new study from the Southwest Research Institute (SwRI) in San Antonio shows that Mars was likely struck by planetesimals early in its history. These large, long-ago collisions introduced "iron-loving" elements to the Red Planet, and those elements, in turn, influenced how quickly the planet formed, according to a statement from SwRI.

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Using Martian meteorite samples found on Earth, the researchers were able to model the mixture of materials that formed the early Martian mantle. The study revealed that Mars received a variety of elements — such as tungsten, platinum and gold — that are attracted to iron as a result of these collisions. 

"To investigate this process, we performed smoothed-particle hydrodynamics impact simulation," Simone Marchi, lead author of the study from SwRI, said in the statement. "Based on our model, early collisions produce a heterogeneous, marble-cake-like Martian mantle."

This illustration shows how early Mars may have looked, with signs of liquid water, large-scale volcanic activity and heavy bombardment from planetary projectiles. (Image credit: SwRI/Marchi)

The meteorite samples suggest that planetesimals bombarded the Red Planet sometime after the planet's primary core formed. That's because "iron-loving" elements like tungsten, platinum and gold generally migrate from a planet's mantle to its central iron core during formation, according to the statement. "Evidence of these elements in the Martian mantle as sampled by meteorites are important because they indicate that Mars was bombarded by planetesimals sometime after its primary core formation ended," SwRI said in the statement.

Earlier studies of the ratio of tungsten isotopes in the Martian meteorite samples suggested that Mars grew rapidly, within 2 million to 4 million years after the solar system began forming, about 4.6 billion years ago. Because tungsten isotopes are produced via radioactive decay processes over time, the ratio of these isotopes in the mantle of Mars provides a clue about the timeline of the planet's formation. 

However, the new models show that early, large collisions could have altered the ratio of elements in the Martian mantle, meaning the planet may have formed over a period of up to 20 million years. 

Researchers at the Southwest Research Institute in San Antonio performed high-resolution simulations of a large projectile hitting early Mars after the planet's core and mantle formed. The projectile's core and mantle particles are indicated by brown and green spheres, respectively, showing how the projectile's materials assimilated into the Martian mantle. (Image credit: SwRI/Marchi)

"Collisions by projectiles large enough to have their own cores and mantles could result in a heterogeneous mixture of those materials in the early Martian mantle," Robin Canup, co-author and assistant vice president of SwRI's Space Science and Engineering Division, said in the statement. "This can lead to different interpretations on the timing of Mars' formation than those that assume that all projectiles are small and homogenous." 

The findings, published Wednesday (Feb. 12) in the journal Science Advances, provide insight on how Mars evolved and how early collisions affected the planet's formation. The Martian meteorites found on Earth are believed to be the result of more recent collisions with the Red Planet. These meteorite samples offer a unique view into Mars' past, as they contain a record of the planet's history, the researchers said.

"To fully understand Mars, we need to understand the role the earliest and most energetic collisions played in its evolution and composition," Marchi said in the statement. 

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  • rod
    Admin said:
    Early cosmic impacts may have influenced the evolution of Mars, suggesting that the Red Planet formed much slower than previously thought.

    Mars took way longer to form than we thought, ancient impacts reveal : Read more

    "To fully understand Mars, we need to understand the role the earliest and most energetic collisions played in its evolution and composition," Marchi said in the statement. "

    Energetic collisions is correct. I did not see anything about the original length of day on Mars compared to the present in the model disclosed. The proto-earth in the giant impact model was spinning slowly if at all, after the giant impact, spun up perhaps 2-3 hour day, now spins 24 hours after tidal dissipation of earth-moon system over 4.5 billion years. What was Mars original axis and spin in this model? Late stage planet formation now in the computer models, features very large impactors with high energy and destruction events. Much change in axis tilt and rotation speeds take place, including planets with little or no rotation in the proto-planet stages in the modeling.
    Reply
  • Torbjorn Larsson
    This is interesting! With this and earlier work we can likely constrain Mars accretion to more or less precisely 10 Myrs after system formation. The paper gives 5-15 Myrs range, but prefers 10 Myrs from average disk dispersal and terrestrial accretion models. (With crust formation within 20 Myrs.) Simultaneously Moon rock dating has been shown to be contaminated and not relevant for dating the system formation, while the Neptune-Kuiper Belt gap as well as inner planet stable formation and Mars + asteroid belt low masses all require an outer system migration within 10 Myrs https://www.sciencemag.org/news/2020/01/cataclysmic-bashing-giant-planets-occurred-early-our-solar-systems-history ]. So we have a consistent 10 Myrs Mars formation date where all the many models work.
    Reply
  • rod
    "we have a consistent 10 Myrs Mars formation date where all the many models work."

    What about the angular momentum of Mars and length of day? What was the proto-Mars rotation rate and axis compared to the present? The final stages of giant impacts create havoc on axis and rotation rates, this is what the new computer models show. Earth and Mars have similar length of days yet the giant impact for the Moon produces a very fast rotating proto-earth, otherwise we do not have a 24 hour day today on earth. I find many free parameters in the computer modeling reports that indicate quite a few adjustments made to get the various models to work and behave well together :)
    Reply
  • Torbjorn Larsson
    rod said:
    "we have a consistent 10 Myrs Mars formation date where all the many models work."

    What about the angular momentum of Mars and length of day? What was the proto-Mars rotation rate and axis compared to the present? The final stages of giant impacts create havoc on axis and rotation rates, this is what the new computer models show. Earth and Mars have similar length of days yet the giant impact for the Moon produces a very fast rotating proto-earth, otherwise we do not have a 24 hour day today on earth. I find many free parameters in the computer modeling reports that indicate quite a few adjustments made to get the various models to work and behave well together :)

    ? I was referring to the models I listed that were affected by the formation timeline.
    Reply
  • rod
    Torbjorn Larsson said:
    ? I was referring to the models I listed that were affected by the formation timeline.

    The link you provided also concluded with words of caution here "The hunt is on for more observations that can parse what happened during those first 100 million years, whether from asteroid samples, clusters of primordial asteroid families, or craters on the Moon and Mars. “Now, the question is, was it a few million years after or 80 million years?” Morbidelli says. “Honestly we don’t know.”

    As I read the material, there is quite a bit of reshuffling of the card deck to harmonize different computer models of accretion and collision to make the planets as well as likely different amount of mass in the ecliptic used too. We see this in some differences like Mercury axis tilt and rotation speed, Venus axis tilt and rotation speed, the Earth-Moon angular momentum problem and solution with Earth axis, tilt, and rotation speed, Mars axis tilt and rotation speed, etc. There are also exoplanets with large masses, several jupiters or more that formed well away from the host star compared to our solar system. Continued research will be done :)
    Reply