The early solar system was a chaotic place, with evidence indicating
that Mars was likely struck by planetesimals, small protoplanets up to 1,200
miles in diameter, early in its history. Southwest Research Institute
scientists modeled the mixing of materials associated with these impacts,
revealing that the Red Planet may have formed over a longer timescale than
previously thought.
An important
open issue in planetary science is to determine how Mars formed and to what
extent its early evolution was affected by collisions. This question is
difficult to answer given that billions of years of history have steadily
erased evidence of early impact events. Luckily, some of this evolution is
recorded in Martian meteorites. Of approximately 61,000 meteorites found on
Earth, just 200 or so are thought to be of Martian origin, ejected from the Red
Planet by more recent collisions.
These meteorites
exhibit large variations in iron-loving elements such as tungsten and platinum,
which have a moderate to high affinity for iron. These elements tend to migrate
from a planet’s mantle and into its central iron core during formation.
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. Studying isotopes of
particular elements produced locally in the mantle via radioactive decay
processes helps scientists understand when planet formation was complete.
“We knew Mars received elements such as platinum and gold from early,
large collisions. To investigate this process, we performed smoothed-particle
hydrodynamics impact simulations,” said SwRI’s Dr. Simone Marchi, lead author
of a Science Advances paper outlining these results.
“Based on our model, early collisions produce a heterogeneous, marble-cake-like
Martian mantle. These results suggest that the prevailing view of Mars
formation may be biased by the limited number of meteorites available for
study.”
Based on the
ratio of tungsten isotopes in Martian meteorites, it has been argued that Mars
grew rapidly within about 2-4 million years after the Solar System started to
form. However, large, early collisions could have altered the tungsten isotopic
balance, which could support a Mars formation timescale of up to 20 million
years, as shown by the new model.
“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,” said
co-author Dr. Robin Canup, assistant vice president of SwRI’s Space Science and
Engineering Division. “This can lead to different interpretations on the timing
of Mars’ formation than those that assume that all projectiles are small and
homogenous.”
The Martian
meteorites that landed on Earth probably originated from just a few localities
around the planet. The new research shows that the Martian mantle could have
received varying additions of projectile materials, leading to variable
concentrations of iron-loving elements. The next generation of Mars missions,
including plans to return samples to Earth, will provide new information to
better understand the variability of iron-loving elements in Martian rocks and
the early evolution of the Red Planet.
“To fully
understand Mars, we need to understand the role the earliest and most energetic
collisions played in its evolution and composition,” Marchi concluded.
Journal article: https://advances.sciencemag.org/content/6/7/eaay2338
Source: https://myfusimotors.com/2020/02/16/mars-simulations-of-early-impacts-produce-a-mixed-mars-mantle/
No comments:
Post a Comment