Blame it On the Tilt
Staying on the topic of Mars this week, there’s a look at a new way of looking at the Red Planet’s ancient past. We all know that Mars’s history has been an enigma for scientist, even as they learn more about it through robotic explorations. Still, after more than 50 years of space missions to Mars, we have questions. Where’s the water? Where WAS the water? When did it flow? What made it flow? Was there a cataclysmic event that changed the face of the planet forever? As it turns out, maybe there’s an idea that helps answer all those questions.
A group of French scientists blames a gigantic structure called the Tharsis Bulge for some of Mars’s most impressive mysteries. They say that Mars experienced a curious “tilt” between 3 and 3.5 billion years ago. It wasn’t an axial tilt, but a shift of the outer layers of the planet (the mantle and crust). They somehow “slipped” around the inner core. That introduced huge changes to the surface that make Mars what it looks like today.
What Caused The Mars Tilt Catastrophe?
A band of scientists using the sciences of geomorphology, geophysics and climatology used observational data from current Mars to explain the Mars of the past. (The team was based at Géosciences Paris Sud (CNRS/Université Paris-Sud), Géosciences Environnement Toulouse (CNRS/Université Toulouse III) and the Laboratoire de Météorrologie Dynamique (CNRS/École polytechnique/UPMC/ENS), together with a researcher from the Lunar and Planetary Laboratory (University of Arizona, U.S.)
Here’s the sequence as the group described it: the gigantic Tharsis volcanic dome began to form nearly 4 billion years ago. It was first located at 20 degrees north latitude (about the location of Hawaii on Earth). It grew taller and wider from repeated volcanic eruptions. Eventually the flows formed a 5,000-kilometer-diameter plateau. (That’s about 3,400 miles, or about the width of North America). This huge volcanic dome was about 12 kilometers deep (about 7.5 miles, or taller than Mt. Everest on Earth), and was extremely massive. Think billions of billions of tons of volcanic deposits distributed in a relatively small part of the planet. That huge mass of rock unbalanced the crust and caused it to shift around. This “Tharsis bulge” migrated to the equator where it lies today, and that shift moved the polar crust, too.
So, if such a shift happened, and the geological evidence may well show that it did, it rearranged the Martian topography. The same theoretical study that speculates on that shift, also shows that Martian rivers containing water from precipitation and ice melt could have flowed at the same time as the formation of the Tharsis bulge. That would make sense, given that climate models from the Laboratoire de Météorologie Dynamique showed a colder, wetter climate with a denser atmosphere than we see today. That would have allowed ice accumulations (such as those suspected to have existed at around latitude 25°S, for example) to melt in response to volcanism, and for water from both the melt and precipitation to flow and create the dry river beds we see today.
So, What Happened to Mars?
Put all these studies together, and you get a slightly different history of Mars of about 3.5 billion years ago. You have a period of liquid water stability that allowed the formation of river valleys on Mars at the same time as the volcanic activity of the Tharsis dome. In fact, the building of the dome may have caused the formation of the river valleys due to volcanic melting of ice. Then, for some reason, the fluvial activity ended some 3.5 billion years ago, and the great tilt triggered by Tharsis’s great heft and influence on the planet took place. That shifted the dome and the poles, and changed the look of the Red Planet.
Since this theory is based on observed geology of Mars, the new geological explanation should be a useful factor as planetary scientists speculate about early Mars and the possibility of life that may have existed in an ancient ocean. I would imagine that these ideas would also help guide future Mars explorers when they get to the Red Planet to study its rocks, plains, mountains, and former oceans, rivers, and lakebeds.