Today, Mars is colloquially known as the “Red Planet” due to its dry, dusty landscape rich in iron oxide (aka “rust”). Additionally, the atmosphere is extremely thin and cold, and no water can exist on the surface in any form other than ice. But as the Martian landscape and other evidence attests, Mars was once a very different place, with a hotter, denser atmosphere and water flowing over its surface. For years, scientists have tried to determine how long natural bodies have existed on Mars and whether or not they were intermittent or persistent.
Another important question is how much water Mars once had and whether or not it was enough to sustain life. According to a new study by an international team of planetary scientists, Mars may have had enough water 4.5 billion years ago to cover it in a global ocean up to 300 meters (nearly 1,000 feet) depth. With organic molecules and other elements distributed throughout the solar system by asteroids and comets at that time, they argue, these conditions indicate that Mars may have been the first planet in the solar system to harbor life.
The study was conducted by researchers from the Institut de physique du globe de Paris (IPGP) at the University of Paris, the Star and Planet Formation Center (StarPlan) at the University of Copenhagen, the Institute of Geochemistry and Petrology (GeoPetro) of ETH Zürich, and the Institute of Physics of the University of Bern. The article describing their research and findings recently appeared in Scientists progress. As they state in their paper, the terrestrial planets underwent a period of heavy asteroid impacts (the late heavy bombardment) after their formation over 4.5 billion years ago.
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These impacts are thought to be 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 the rocky planets of the inner solar system – particularly with regard to the distribution of volatile elements like water – is still debated. For the purposes of their study, the international team reported on the variability of a single chromium isotope (54Cr) in Martian meteorites dated to 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 flying into space.
In other words, the composition of these meteorites represents the original crust of Mars before the 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. Therefore, 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 stated in a UCPH faculty press release:
“Plate tectonics on Earth has erased all evidence of what happened during the first 500 million years of our planet’s history. Plates are constantly moving and being recycled and destroyed inside our In contrast, Mars does not have such plate tectonics that the planet’s surface retains 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 ca. 4.5 billion years ago and the amount of water they provided. According to their results, there would have been enough water to cover the entire planet in an ocean at least 300 meters deep (~1000 feet) and up to 1 km (0.62 mi) deep in some areas. . In comparison, there was very little water on Earth at that time because a Mars-sized object had collided with Earth, resulting in the formation of the Moon (i.e. the large impact hypothesis).
In addition to water, asteroids also delivered organic molecules like amino acids (the building blocks of DNA, RNA, and protein cells) to Mars during the late bombardment. As Bizarro explained, this means that life could have existed on Mars when the Earth was barren:
“This happened during the first 100 million years of Mars. After this period, something catastrophic happened to potential life on Earth. It is believed that there was a gigantic collision between the Earth and another Mars-sized planet It was an energetic collision that formed the Earth-Moon system and, at the same time, wiped out all potential life on Earth.
This study is similar to recent research that used the deuterium-hydrogen ratios of Martian meteorites to create models of atmospheric evolution. Their findings showed that Mars may have been covered in oceans when Earth was still just a ball of molten rock. These and other questions related to the geological and environmental evolution of Mars will be further investigated by robotic missions to Mars during this decade (followed by crewed missions in the 2030s).
Further reading: University of Copenhagen
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