Mars today is almost completely geologically inert, but it was not always the case. Researchers believe they have identified a process that created the previously inexplicable Medusae fossil formations on the planet's surface. Researchers have used data from routing spacecraft to point their finger at a massive volcanic event in Mars's past, making Medusae Fossae the largest structure of its kind in the solar system.
The Medusae Fossae region was originally identified in the 1960s by NASA's earliest orbital mission to Mars. Medusae Fossae covers an area of approximately 1.24 million square kilometers near the Martian Equator, one fifth of continental America. The formation is marked by long ridges, deep valleys and expansive flat mesas. It is completely different from all the surrounding geography, but no one could decide how it was formed.
New research from Johns Hopkins University now suggests that a massive volcanic event about 3 billion years ago is guilty of Medusae Fossae's existence. The team used data from spacecraft like Mars Reconnaissance Orbiter to measure the density of rocks in Medusae Fossae for the first time. They found that Medusae Fossae is porous with an average density of two thirds of the rest of Mars crust. Radar and gravity testing excludes ice build-up as the reason for the lower density.
Porous rocks like this usually suggest a volcanic origin – it is volcanic ashes that eventually cement in stone. This is much of volcanic rock. In fact, the study estimates that erosion has cleared about half of the original Medusae Fossae rock. Even in its current state, Medusae Fossae is the largest known explosive volcanic deposition in the solar system. It's more than 66 times as big as Fish Canyon Tuff, the next biggest deposit, you'll find in Colorado right here on earth.
The presence of a large volcanic residue as this points to major changes in the Mars environment 3 billion years ago. That eruption would have released enough water to cover the entire planet in a shallow sea up to four inches deep. It would also have belched enough carbon dioxide to raise global temperatures. It would of course have come with toxic volcanic gases such as hydrogen sulphide and sulfur dioxide. If we learn more about the effects of this outbreak, we can get a better idea of whether Mars was ever habitable.