Today, Mars is popularly known as the “Red Planet” because its dry, dusty landscape is rich in iron oxide (also known as “rust”). In addition, 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 confirm, 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 they were intermittent or persistent.
Another important question is how much water Mars once had and whether this was enough to support life. Mars may have had enough water to cover it in a global ocean up to 300 meters (almost 1,000 feet) deep, 4.5 billion years ago, according to a new study by an international team of planetary scientists. Together with organic molecules and other elements currently being scattered throughout the solar system by asteroids and comets, they argue, these conditions indicate that Mars may have been the first planet in the solar system to support life.
The study was conducted 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 of Geochemistry and Petrology (GeoPetro) at the ETH Zurich, and the Physics Institute of the University of Bern. The article describing their research and findings was recently published in Scientific progress. As they point out in their paper, the terrestrial planets endured a period of significant asteroid impacts (the late heavy bombardment) after their formation more than 4.5 billion years ago.
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These effects are believed 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 rocky planets in the inner solar system is still debated – particularly regarding the distribution of volatile elements such as water. For their study, the international team reported on the variability of a single chromium isotope (54Cr) in Martian meteorites dating from this early period. These meteorites were part of the Martian crust at the time and were ejected as a result of asteroid impacts that sent them into space.
In other words, the composition of these meteorites represents the original Martian crust before asteroids deposited water and various elements on the surface. Because Mars does not have active plate tectonics like Earth, its surface is not subject to constant convection and recycling. Therefore, meteorites ejected from Mars billions of years ago provide a unique insight into what Mars was like shortly after the solar system’s planets formed. As co-author Professor Bizzarro of the StarPlan Center said in a UCPH faculty press release:
“Plate tectonics on Earth have erased all evidence of what happened in the first 500 million years of our planet’s history. The plates are constantly moving and being carried back and destroyed in the interior of our planet. Mars, on the other hand, 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 about 4.5 billion years ago and how much 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 (~1,000 feet) and up to 1 km (0.62 mi) deep in some areas. By comparison, there was very little water on Earth at the time because a Mars-sized object had collided with Earth, leading to the formation of the Moon (i.e. the Grand Impact Hypothesis).
In addition to water, asteroids also scattered organic molecules such as amino acids (the building blocks of DNA, RNA and protein cells) to Mars during the late heavy bombardment. As Bizarro explained, this means life could have existed on Mars when Earth was barren:
“This happened in the first 100 million years of Mars. After this period, something catastrophic for potential life on Earth happened. It is believed that there was a giant collision between the Earth and another planet the size of Mars. It was an energetic collision that formed 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 create models of atmospheric evolution. Their findings showed that Mars may have been covered with oceans when Earth was still a molten ball of rock. These and other questions related to the geological and ecological evolution of Mars will be further explored in this decade by robotic missions destined for Mars (followed by manned missions in the 2030s).
Further reading: University of Copenhagen