Mars formed slowly over 20 million years – drawing in particles of asteroids up to 1,200 miles in diameter that SMASHED into its core
- Mars formed over a much longer period than originally thought, say a US team
- Mars was bombarded by rocky objects after its primary core formation ended
- The researchers simulated particles from a large, projectile hitting early Mars
Mars took 20 million years to become the big rusty globe that it is today, according to a new study – almost 15 million years longer than previously suggested.
US scientists think up to three large asteroids around 620 to 1,240 miles (1,000 to 2,000km) in diameter may have hit the planet relatively early in its development.
They think the planet then formed gradually, accumulating mass by pulling particles into its gravitational field that bulked it up to reach its current 4,200-mile diameter.
The study contradicts previous theories that the Red Planet grew rapidly in the space of just 2 billion to 4 billion years after the Solar System started to form.
A Southwest Research Institute team performed high-resolution, smoothed-particle simulations of a large, differentiated projectile hitting early Mars after its core and mantle had formed. The projectile’s core and mantle particles are indicated by brown and green spheres respectively, showing local concentrations of the projectile materials assimilated into the Martian mantle
There are around 200 Martian meteorites on Earth, thought to have been ejected from the Mars during collisions with large asteroids.
In the past, scientists have used these Martian meteorites to construct a timeline of the planet’s formation and map its mysterious history.
But due to a limited number of meteorites available for research, the scientists think the ‘prevailing view of Mars’ formation may be biased’.
The team based their findings on computer modelling simulations of an asteroid hitting Mars that took place after the formation of its core and mantle – the layer surrounding the core.
‘We knew Mars received elements such as platinum and gold from early, large collisions,’ said lead author of the study Dr. Simone Marchi at Southwest Research Institute in San Antonio, Texas.
‘To investigate this process, we performed smoothed-particle hydrodynamics impact simulations.
‘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.’
Scientists developed this illustration of how early Mars may have looked, showing signs of liquid water, large-scale volcanic activity and heavy bombardment from planetary projectiles. SwRI is modelling how these impacts may have affected early Mars to help answer questions about the planet’s evolutionary history
Of approximately 61,000 meteorites found on Earth, just 200 or so are thought to be of Martian origin.
Samples show variations in elements such as tungsten, platinum and gold, which indicate Mars was bombarded by asteroids some time after its primary core formation ended.
‘We knew Mars received elements such as platinum and gold from early, large collisions,’ said Dr Marchi, whose study was published in Science Advances.
‘To investigate this process, we performed smoothed-particle hydrodynamics impact simulations.
‘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.’
The previous estimate of rapid growth between two billion to four billion years was based on analysis of tungsten in the Martian meteorites.
Elements such as tungsten 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 found in these meteorites, indicate that Mars was bombarded by rocky space debris sometime after its primary core formation ended.
Large, early collisions could have altered the balance of tungsten, which could support a Mars formation timescale of up to 20 million years, as shown by the new model.
‘To fully understand Mars, we need to understand the role the earliest and most energetic collisions played in its evolution and composition,’ Marchi said.
NASA’s Mars 2020 Rover will pick up samples of rock and soil from the red planet, deposit them in tubes and leave them on the ground for a future mission to return them to Earth.
The next generation of Mars missions, including plans to return samples to Earth, could provide new information on the variability of iron-loving elements in Martian rocks and the early evolution of the Red Planet.
This July, NASA’s Mars 2020 mission will take off with a touchdown on the Martian surface set for February 2021.
The six-wheeled robotic lander will anal;yse the dusty surface of the planet to seek signs of habitable conditions or microbial life in its past.
The Mars 2020 rover’s drill can collect core samples of rocks and soils and set them aside in a ‘cache’ on the surface of Mars.
A future mission could potentially return these samples to Earth.
The European Space Agency and Russia’s Roscosmos will also launch the ‘Rosalind Franklin rover’ this summer as part of the next stage of their ExoMars project to find signs of past life on Mars.
WHAT EVIDENCE DO SCIENTISTS HAVE FOR LIFE ON MARS?
The search for life on other planets has captivated mankind for decades.
But the reality could be a little less like the Hollywood blockbusters, scientists have revealed.
They say if there was life on the red planet, it probably will present itself as fossilized bacteria – and have proposed a new way to look for it.
Here are the most promising signs of life so far –
Water
When looking for life on Mars, experts agree that water is key.
Although the planet is now rocky and barren with water locked up in polar ice caps there could have been water in the past.
In 2000, scientists first spotted evidence for the existence of water on Mars.
The Nasa Mars Global Surveyor found gullies that could have been created by flowing water.
The debate is ongoing as to whether these recurring slope lineae (RSL) could have been formed from water flow.
Meteorites
Earth has been hit by 34 meteorites from Mars, three of which are believed to have the potential to carry evidence of past life on the planet, writes Space.com.
In 1996, experts found a meteorite in Antarctica known as ALH 84001 that contained fossilised bacteria-like formations.
However, in 2012, experts concluded that this organic material had been formed by volcanic activity without the involvement of life.
Signs of Life
The first close-ups of the planet were taken by the 1964 Mariner 4 mission.
These initial images showed that Mars has landforms that could have been formed when the climate was much wetter and therefore home to life.
In 1975, the first Viking orbiter was launched and although inconclusive it paved the way for other landers.
Many rovers, orbiters and landers have now revealed evidence of water beneath the crust and even occasional precipitation.
Earlier this year, Nasa’s Curiosity rover found potential building blocks of life in an ancient Martian lakebed.
The organic molecules preserved in 3.5 billion-year-old bedrock in Gale Crater — believed to have once contained a shallow lake the size of Florida’s Lake Okeechobee — suggest conditions back then may have been conducive to life.
Future missions to Mars plan on bringing samples back to Earth to test them more thoroughly.
Methane
In 2018, Curiosity also confirmed sharp seasonal increases of methane in the Martian atmosphere.
Experts said the methane observations provide ‘one of the most compelling’ cases for present-day life.
Curiosity’s methane measurements occurred over four-and-a-half Earth years, covering parts of three Martian years.
Seasonal peaks were detected in late summer in the northern hemisphere and late winter in the southern hemisphere.
The magnitude of these seasonal peaks – by a factor of three – was far more than scientists expected.
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