Why Did The Water On Mars Disappear?

Perseverance Rover
Image credit: NASA/JPL-Caltech

The red planet has been an object of fascination to us for thousands of years. Going from a god of war to a potential alien world with alien people and large canals to our current view of a dry desert like planet. However, we find a lot of evidence that this was not always the case, evidence that points towards Mars once being a place filled with seas, rivers and lakes just like Earth. So what happened?

The Mars water mystery

The mystery of Mars’ water has been the focus of many planetary scientists for decades now, with theories yo-yo-ing between it always having been dry to the planet being covered with oceans at some point.

These days we are quite sure that there was once water. We find eroded rocks, meandering channels and deltas on the surface of Mars that closely resemble those made by rivers back home. And, of course, there is the actual ice that covers the pole caps and hides under the surface.

This means that the question is no longer ‘is there water?’ but rather ‘where did it go?’, and scientists think that they can finally answer this after combining the data from several rovers and meteorite samples. Like most mysteries, this one has multiple causes that worked together.

Mars loses its magnetic field

The first problems started when the red planet’s molten core solidified, putting an end to plate tectonics as well as the magnetic field that protected the planet.

The magnetic field is important because it diverts a large amount of the Sun’s ionizing radiation, protecting the delicate balance of the planet below. Without this field, these charged particles collide with the atmosphere and react with it, slowly stripping it away over the course of billions of years in a way comparable to sandpaper. Depending on how much water was in the atmosphere at this point, Mars could have lost between 10 and 70% of its water this way.

Remaining water disappears into ground

The remaining water seems to have disappeared into the ground, binding chemically to various types of rocks and minerals. This process is well known and happens on Earth also, but we get the water back due to the activity in the core in the form of volcanic eruptions. Without such a process, the water bound in rock layers is stuck. In total, scientists estimate that between 30 and 99% of the water that once flowed on Mars is trapped in this way. This is enough to cover the entire planet in a sea that is between 100 and 1500 meters deep. Some scientists think that we could use this water when colonizing Mars, but others claim that there is no energy efficient way of doing this.

Perseverance Rover to bring Martian rocks/soil back to Earth

The Perseverance rover that landed on the 18th of February is tasked with collecting and return rock and soil samples from the Jezero Crater and cache them in an accessible place on the surface for potential return to Earth. Study of this rocks will undoubtedly give more information about the validity of the theory and the percentages of water that are locked in the planet’s crust.

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