Today, Mars is colloquially known as the “Red Planet” because its dry, dusty landscape is rich in iron oxide (aka “rust”). In addition, the atmosphere is extremely thin and cold, and water in any form other than ice cannot exist on the surface. But as the Martian landscape and other lines of evidence show, Mars was once a very different place, with a warmer, denser atmosphere and flowing water on its surface. For years scientists have tried to determine how long natural bodies existed on Mars and whether or not they were intermittent or persistent.
Another important question is how much water Mars once had and whether it was enough to support life. Mars may have had enough water to cover it in a global ocean as deep as 300 meters (nearly 1,000 feet) 4.5 billion years ago, according to a new study by an international team of planetary scientists. Along with organic molecules and other elements being carried around the solar system by asteroids and comets at the time, they argue, these conditions suggest Mars may have been the first planet in the solar system to support life.
The study was carried out by researchers from the Institut de Physique du Globe de Paris (IPGP) at the University of Paris, the Center for Star and Planet Formation (StarPlan) at the University of Copenhagen, the Institute for Geochemistry and Petrology (GeoPetro) at ETH Zurich, and the Physical Institute of the University of Bern. The paper describing their research and findings recently appeared in scientific advances. As they state in their article, the terrestrial planets suffered a period of significant asteroid impact (the Late Heavy Bombardment) after their formation over 4.5 billion years ago.
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These effects are believed to be due to how water and the building blocks of life (organic molecules) were distributed throughout the solar system. However, the role of this period in the evolution of rocky planets in the inner Solar System – particularly in the distribution of volatile elements such as water – is still debated. For their study, the international team reported the variability of a single chromium isotope (54Cr) in Martian meteorites from this early period. These meteorites were part of the crust of Mars at the time and were ejected due to asteroid impacts that sent them into space.
In other words, the composition of these meteorites represents the original crust of Mars before asteroids deposited water and various elements on the surface. Since Mars does not have active plate tectonics like Earth, the surface is not subject to constant convection and recycling. As such, meteorites ejected from Mars billions of years ago offer a unique insight into what Mars looked like shortly after the planets of the solar system formed. As co-author Professor Bizzarro of the StarPlan Center said in a UCPH faculty press release:
“Plate tectonics on Earth has wiped out all evidence of what happened in the first 500 million years of our planet’s history. The plates are constantly moving and being recycled and destroyed in the interior of our planet. In contrast, Mars has no plate tectonics, so the planet’s surface preserves a record of the planet’s earliest history.”
By measuring the variability of 54Cr in these meteorites, the team estimated the impact rate for Mars around 4.5 billion years ago and how much water they supplied. According to their findings, there would have been enough water to cover the entire planet in an ocean at least 300 meters (~1000 feet) deep and in some areas up to 1 km (0.62 miles) deep. In comparison, there was very little water on Earth at the time because a Mars-sized object collided with Earth, leading to the formation of the Moon (i.e. the Grand Impact Hypothesis).
In addition to water, asteroids also spilled organic molecules such as amino acids (the building blocks of DNA, RNA, and protein cells) onto Mars during the late heavy bombardment. As Bizarro explained, this means that life could have existed on Mars when Earth was sterile:
“This happened within the first 100 million years of Mars. After that time, something catastrophic for potential life on Earth happened. It is believed that there was a gigantic collision between Earth and another Mars-sized planet. It was an energetic collision that shaped the Earth-Moon system while simultaneously wiping out all potential life on Earth.”
This study is similar to recent research that used the deuterium-to-hydrogen ratios of Martian meteorites to model atmospheric evolution. Their results showed that Mars may have been covered by oceans when Earth was a molten ball of rock. These and other questions related to the geological and ecological evolution of Mars will be further explored by robotic missions destined for Mars in this decade (followed by manned missions in the 2030s).
Further reading: University of Copenhagen
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