Mars once had enough water for a 1,000-foot-deep planetary ocean

Today, Mars is known colloquially as the “Red Planet” due to how its dry, dusty landscape is rich in iron oxide (aka “rust”). Furthermore, the atmosphere is extremely thin and cold, and no water other than ice can exist on the surface. But as the Martian landscape and other lines of evidence attest, Mars was once a very different place, with a hotter, denser atmosphere and water flowing across its surface. For years, scientists have attempted 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 that was enough to support life. 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) deep, according to a new study by an international team of planetary scientists. Together with organic molecules and other elements distributed throughout the Solar System by asteroids and comets at this time, 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) of the University of Paris, the Center for Star and Planet Formation of the University of Copenhagen (StarPlan), the Institute of Geochemistry and Petrology (GeoPetro) of ETH Zurich, and the Physics Institute of the University of Bern. The paper describing their research and findings recently appeared at The progress of science. As they indicate in their paper, the terrestrial planets experienced a period of significant asteroid impacts (the Late Heavy Bombardment) following their formation over 4.5 billion years ago.

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Scientists theorize that comets and asteroids distributed water and organic molecules to rocky planets during the Late Heavy Bombardment period. Credit: NASA/JPL-Caltech

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 rocky planets in the inner Solar System, particularly with regards to the distribution of volatile elements such as water, is still debated. For the sake of 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 crust of Mars at the time and were ejected in 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. Because Mars doesn’t have active plate tectonics like Earth does, the surface isn’t subject to constant convection and recycling. Thus, meteorites ejected from Mars billions of years ago offer 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 put it in a UCPH faculty press release:

“Plate tectonics on Earth has erased all evidence of what happened in the first 500 million years of our planet’s history. The plates are constantly moving and are recycled and destroyed within our planet. In contrast, Mars does not have plate tectonics such that the planet’s surface retains a record of the planet’s early 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 released. 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 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 Great Impact Hypothesis).

In addition to water, the asteroids also distributed organic molecules such as amino acids (the building blocks of DNA, RNA and protein cells) to Mars during the late bombardment. As Bizarro explained, this means that life may have existed on Mars when Earth was barren:

“This happened in the first 100 million years of Mars. After this period, something catastrophic happened for potential life on Earth. There is believed to have been a giant collision between Earth and another planet the size of Mars. 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 model atmospheric evolution. Their findings showed that Mars may have been covered by oceans when the Earth was still 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 this decade (followed by manned missions in the 1930s).

Further reading: University of Copenhagen

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