As evidence mounts that Mars once had oceans, new maps are shedding light on what a watery Mars would look like.
Evidence of Former Oceans
The Mars Ocean Hypothesis states that nearly a third of the surface of Mars was covered by an ocean of liquid water early in the planet’s geologic history. This primordial ocean, dubbed Oceanus Borealis, would have filled the Vastitas Borealis basin in the northern hemisphere, a region which lies 4–5 km (2.5–3 miles) below the mean planetary elevation, at a time period of approximately 3.8 billion years ago. Evidence for this ocean includes geographic features resembling ancient shorelines, and the chemical properties of the Martian soil and atmosphere. Early Mars would have required a denser atmosphere and warmer climate to allow liquid water to remain at the surface.
Several physical features in the present geography of Mars suggest the existence of a primordial ocean. Networks of gullies that merge into larger channels imply erosion by a liquid agent, and resemble ancient riverbeds on Earth. Enormous channels, 25 km wide and several hundred meters deep, appear to direct flow from underground aquifers in the Southern uplands into the Northern plains. Much of the northern hemisphere of Mars is located at a significantly lower elevation than the rest of the planet (the Martian dichotomy), and is unusually flat. Along the margins of this region are physical features suggestive of ancient shorelines. Sea level must follow a line of constant gravitational potential. After adjustment for polar wander caused by mass redistributions from volcanism, the Martian paleo-shorelines meet this criterion. The Mars Orbiter Laser Altimeter (MOLA), which accurately determined the altitude of all parts of Mars, found that the watershed for an ocean on Mars covers three-quarters of the planet.
The Terraforming of Mars
The terraforming of Mars is the hypothetical process by which the climate, surface, and known properties of Mars would be deliberately changed with the goal of making it habitable by humans and other terrestrial life, thus providing the possibility of safe and sustainable colonization of large areas of the planet. The concept is reliant on the assumption that the environment of a planet can be altered through artificial means; the feasibility of creating an unconstrained planetary biosphere is undetermined. There are several proposed methods, some of which present prohibitive economic and natural resource costs, and others which may be currently technologically achievable.
Terraforming Mars would entail three major interlaced changes: building up the atmosphere, keeping it warm, and keeping the atmosphere from being lost into outer space. The atmosphere of Mars is relatively thin and thus has a very low surface pressure of 0.6 kilopascals (0.087 psi); compared to Earth with 101.3 kilopascals (14.69 psi) at sea level and 0.86 kilopascals (0.125 psi) at an altitude of 32 kilometres (20 mi). The atmosphere on Mars consists of 95% carbon dioxide (CO2), 3% nitrogen, 1.6% argon, and contains only traces of oxygen, water, and methane. Since its atmosphere consists mainly of CO2, a known greenhouse gas, once the planet begins to heat, more CO2 enters the atmosphere from the frozen reserves on the poles, adding to the greenhouse effect. This means that the two processes of building the atmosphere and heating it would augment one another, favoring terraforming. However, on a large scale, controlled application of certain techniques over enough time to achieve sustainable changes would be required to make this hypothesis a reality.
Significance for Earth today
The better that we can understand how Mars went from a water rich planet with a thicker atmosphere to a dry desert with an atmosphere mostly of CO2, the better we will be able to avoid the same fate. If we learn that the build up of CO2 was a sudden process whereby a ‘tipping point’ of environmental conditions is reached, our current situation may be more urgent than previously believed.