Along the Martian equator, there is a structure that stretches for about 5,000 kilometers (3,100 miles), roughly the distance between New York and LA. It is called the Medusae Fossae Formation and planetary scientists have been struggling to explain how it came to be. Now, they think it was the consequence of explosive volcanism.
The mystery of the Medusae Fossae started decades ago. Visually the region is both a smooth, gently undulating surface due to erosion, and a carved plateau full of ridges, grooves, and mesas. But it’s radar observations that have deepened the questions about its origin. These observations suggested that the region could be made by volcanic porous rocks or ice deposits.
As reported in the Journal of Geophysical Research: Planets, the study suggests about 3 billion years ago, a massive volcanic explosion threw ash, rocks and a large volume of gas and water into the Martian atmosphere. The eruption released enough water to cover the entire planet in a wet layer 9 centimeters (3.5 inches) thick and left a deposit region – Medusae Fossae – about one-fifth the size of the continental United States.
"This is a massive deposit, not only on a Martian scale, but also in terms of the solar system, because we do not know of any other deposit that is like this," lead author Lujendra Ojha, from Johns Hopkins University, said in a statement.
"If you were to distribute the Medusae Fossae globally, it would make a 9.7-meter (32-foot) thick layer. Given the sheer magnitude of this deposit, it really is incredible because it implies that the magma was not only rich in volatiles and also that it had to be volatile-rich for long periods of time."
This was probably the largest known explosive volcanic deposit in our Solar System. Researchers think the eruption could have contributed to warming the climate of the Red Planet and the volcanic gases released altered the chemistry of Mars' surface and atmosphere, prolonging this period.
The new study uses gravity data from several spacecraft orbiting Mars doing different analyses. They estimated the density of the rocks in the Medusae Fossae, and discovered that it is about two-thirds less dense than the rest of the Martian crust. It is most likely a porous rock as ice is much lower density. The team estimated that about half of the original deposit of the eruption as now eroded away.
This finding suggests that Martian interior is more complex than previously thought. To have created such a structure made of porous rocks on Mars' surface means that a lot of volatile substances must be present in the planet’s interior.