Ancient volcanoes formed Mars's Medussae Fossae region

Volcanic eruptions could have warmed Mars enough for its surface to have supported liquid water.
By Laurel Kornfeld | Oct 25, 2018
Mars's Medussae Fossae Formation, a region near the Martian equator composed of eroding sediments, may have been formed by ancient volcanic eruptions more than three billion years ago.

Composed of soft rock, this area, which was imaged by NASA's Mars Reconnaissance Orbiter (MRO) in infrared wavelengths, is a massive region composed of ridges, valleys, and mesas. It has been described by NASA scientists as "an enigmatic pile of eroding sediments."

First discovered during the 1960s by NASA's Mariner spacecraft, Medussae Fossae and its exotic terrain and soft rock puzzled scientists, who were unable to determine whether it was created by wind, ice, water, or volcanoes.

Now, using MRO data, researchers at Johns Hopkins University in Baltimore measured the terrain's density and found its porous surface to have likely been formed by explosive volcanic deposits rather than by ice deposits.

"The eruptions that created the deposit could have spewed massive amounts of climate-altering gases into Mars's atmosphere and ejected enough water to cover Mars in a global ocean," said Lujendra Ojha of Johns Hopkins University.

Medussaa Fossae is the largest known explosive volcanic deposit in the solar system, about 100 times more massive than the largest explosive volcanic deposit on Earth.

Gases emitted during the ancient eruptions could have warmed the planet enough for liquid water to have existed on the Red Planet's surface. However, they also would have changed Mars's atmosphere and surface by spewing hydrogen sulfide and sulfur dioxide, both of which are toxic gases.

Since the ancient eruptions, as much as half of the original rock at the site has eroded away, leaving behind the ridges and valleys.

"Future gravity surveys could help distinguish between ice, sediments, and igneous rocks in the upper crust of the planet," noted Kevin Lewis, also of Johns Hopkins University.

Sedimentary rocks are deposited and solidify in layers and are usually transported by water and wind. Igneous rocks are formed when molten magma brought by volcanoes solidifies.

These findings are evidence that Mars's interior is significantly more complex than scientists initially thought.

"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," Ojha stated.

Findings of the study have been published in the Journal of Geophysical Research: Planets.

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