Bomb Sag Study Provides More Evidence of Early Water on Mars

Posted on May 5, 2012

The atmosphere on Mars is less than 1% the density of Earth's. This is one of the main reasons liquid water cannot exist on the surface of Mars. Scientists believe the atmosphere on early Mars was much denser.

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 made by the Mars rover Spirit. His new findings, published here in the journal Geophysical Research Letters, 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.

Dufek says, "Atmospheric pressure has likely played a role in developing almost all Mars' surface features. 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 and created a divot, which is also known as a bomb sag. The deposit 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. The bomb sag on the surface of Mars is pictured above.

Dufek and his team created bomb sags in the lab by propelling particles of varying materials (glass, rock and steel) into sand beds (made using grains the same size as those observed by Spirit on Mars). The particles were propelled at different speeds into dry, damp and saturated sand beds. They then compared the bomb sags created in the lab with the Martian bomb sag. The study found that only the impacts in the saturated sand beds produced depositional features consistent with the rover's observations on Mars.

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.

Dufek says, "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. 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."

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