Mars’ Volcanic Eruptions Point to an Ancient Atmosphere Dense With Water



The atmosphere of Mars is less than 1 percent the density of Earth’s. It’s one of the reasons liquid water covers much of our planet but cannot exist on the Red Planet. As more research points toward the possibility of water on early Mars, scientists have increased their studies on the density of its atmosphere billions of years ago. It’s not an easy task. In fact, it’s very difficult to even determine Earth’s atmospheric pressure from the same time frame.

Georgia Tech Assistant Professor Josef Dufek is attempting to learn more about the past atmospheric conditions by analyzing two unlikely sources: ancient volcanic eruptions and surface observations by the Mars rover Spirit. His new findings provide more evidence that early Mars was saturated with water and that its atmosphere was considerably thicker, at least 20 times more dense, than it is today.

“Atmospheric pressure has likely played a role in developing almost all Mars’ surface features,” said Dufek, an instructor in the School Earth and Atmospheric Sciences. “The planet’s climate, the physical state of water on its surface and the potential for life are all influenced by atmospheric conditions.”

Dufek’s first research tool was a rock fragment propelled into the Martian atmosphere during a volcanic eruption roughly 3.5 billion years ago. The deposit landed in the volcanic sediment, created a divot (or bomb sag), eventually solidified and remains in the same location today. Dufek’s next tool was the Mars rover. 

In 2007, Spirit landed at that site, known as Home Plate, and took a closer look at the imbedded fragment. Dufek and his collaborators at the University of California-Berkeley received enough data to determine the size, depth and shape of the bomb sag.

Dufek and his team then went to the lab to create bomb sags of their own. They created beds of sand using grains the same size as those observed by Spirit. The team propelled particles of varying materials (glass, rock and steel) at different speeds into dry, damp and saturated sand beds before comparing the divots with the bomb sag on Mars. No matter the type of particle, the saturated beds consistently produced impact craters similar in shape to the Martian bomb sag.

By varying the propulsion speeds, Dufek’s team also determined that the lab particles must hit the sand at a speed of less than 40 meters per second to create similar penetration depths. In order for something to move through Mars’ atmosphere at that peak velocity, the pressure would have to be a minimum of 20 times more dense than current conditions, which suggests that early Mars must have had a thicker atmosphere. Click here for a video demonstration.

“Our study is consistent with growing research that early Mars was at least a transiently watery world with a much denser atmosphere than we see today,” said Dufek. “We were only able to study one bomb sag at one location on the Red Planet. We hope to do future tests on other samples based on observations by the next rover, Curiosity.”

The image at top of page is the Mars Global Surveyor view of the Tharsis region showing the volcanoes (covered by blue-white clouds) and the Valles Marineris canyon (lower right). 

The highest point in the solar system that we know about rises up in the Tharsis region. This shield volcano called Olympus Mons (Mt. Olympus from Greek mythology) towers 16 miles (25 kilometers) above the surrounding plains, and its base spans 370 miles (600 kilometers). In contrast, the largest volcano on Earth is Mauna Loa in Hawaii, which rises 6 miles (10 kilometers) above the ocean floor and is 140 miles (225 kilometers) wide at its base.

At the edge of the Tharsis region is a large system of canyons called Valles Marineris. Valles Marineris is 2,500 miles (4,000 kilometers) long. That's greater than the distance from New York to Los Angeles. The canyons are 370 miles (600 kilometers) wide and 26,400 feet (5 to 6 miles or 8 to 10 kilometers) deep. That makes Valles Marineris much larger than the Grand Canyon. Unlike our national landmark, which formed from water erosion from the Colorado River, Valles Marineris was created by the crust cracking when the Tharsis bulge formed.

Curiosity is scheduled to land on Mars on August 5.

The Daily Galaxy via Georgia Institute of Technology

Image credit: NASA/JPL/Malin Space Science Systems

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