A team of US researchers has found new 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.
To learn more about the past atmospheric conditions on the Red Planet, the researchers analyzed two unlikely sources: ancient volcanic eruptions and surface observations by the Mars rover Spirit. Their findings appear in the journal Geophysical Research Letters.
“Atmospheric pressure has likely played a role in developing almost all Mars’ surface features,” said study co-author Dr. Josef Dufek, an assistant professor at the Georgia Institute of Technology. “The planet’s climate, the physical state of water on its surface and the potential for life are all influenced by atmospheric conditions.”
The first research tool used by the team 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.
The 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, so the team had enough data to determine the size, depth and shape of the bomb sag.
The researchers then created bomb sags of their own. They formed beds of sand using grains the same size as those observed by Spirit, and 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, the team also determined that the lab particles must hit the sand at a speed of less than 40 m 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.
“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,” Prof. Dufek concluded. “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.”