Washington, June 26 : A new analysis of Martian soil data by geoscientists suggests that there was once enough water in the Red Planet's atmosphere for a light drizzle or dew to hit the ground, leaving tell-tale signs of its interaction with the planet's surface.
The study's conclusion breaks from the more dominant view that the liquid water that once existed during the red planet's infancy came mainly in the form of upwelling groundwater rather than rain.
To come up with their conclusions, researchers from UC Berkeley in the US used published measurements of soil from Mars that were taken by various NASA missions: Viking 1, Viking 2, Pathfinder, Spirit and Opportunity.
According to Ronald Amundson, UC Berkeley professor of ecosystem sciences and the study's lead author, the dominant view, put forward by many now working on the Mars missions, is that the chemistry of Mars soils is a mix of dust and rock that has accumulated over the eons, combined with impacts of upwelling groundwater, which is almost the exact opposite of any common process that forms soil on Earth.
"In this paper, we try to steer the discussion back by re-evaluating the Mars data using geological and hydrological principles that exist on Earth," he said.
While the UC Berkeley-led study does not delve directly into evidence of life on Mars, it does suggest what kind of climate that life, if it existed, might have encountered.
The planet is currently too cold for water to exist in a liquid state, but scientists generally agree that during the planet's earliest geological period, known as the Noachian epoch and dating 4.6 billion to 3.5 billion years ago, there were enough atmospheric greenhouse gases to warm the air and support lakes and flowing rivers.
According to Amundson, many scientists believe that by the time the planet moved from the Noachian epoch to the Hesperian epoch, dating from 3.5 billion to 1.8 billion years ago, water on Mars had either frozen or evaporated.
The new study, however, suggests that liquid water existed in the Martian atmosphere into the Hesperian era.
To support this view, the team showed that soil at the Viking, Pathfinder and Spirit landing sites had lost significant fractions of the elements that make up the rock fragments from which the soil was formed, a sign that water once moved downward through the dirt, carrying the elements with it.
Amundson also pointed out that the soil records a long period of drying, as evidenced by surface patterns of the now sulfate-rich land.
The researchers also noted that the distribution of the chemical elements in Martian soil, where sulfates accumulate on the surface with layers of chloride salt underneath, suggest atmospheric moisture.