Life on Mars? Not on the surface
Mars may have been an arid planet for over 600 million years, making it too hostile for any life to survive on the planet's surface.
Indeed, a research team led by Dr. Tom Pike of London’s Imperial College spent three years analyzing Martian soil collected during the 2008 NASA Phoenix mission to the northern arctic region of the red planet.
Results indicate the surface of Mars has been arid for hundreds of millions of years - despite the presence of ice and the fact that previous research claimed Mars may have had a warmer and wetter period in its earlier history more than three billion years ago.
In addition, the team estimated that the soil on Mars had been exposed to liquid water for 5,000 years - at most - since its formation billions of years ago.
According to Pike, satellite images and previous studies have proven the soil on Mars is uniform across the planet, which suggests results from the team's analysis could be applied to all of Mars. This implies that liquid water has been on the surface of Mars for far too short a time for life to maintain a foothold on the surface.
"We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years," Pike explained.
"We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life. Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground."
During the Phoenix mission, Pike his research group formed one of 24 teams based at mission control in the University of Arizona, operating part of the spacecraft's onboard laboratories. They analyzed soil samples dug up by a robot arm, using an optical microscope to produce images of larger sand-sized particles, along with an atomic-force microscope to produce 3D images of the surface of particles as small as 100 microns across.
The scientists looked looked for microscopic clay particles that are formed when rock is broken down by water. Such particles are an important marker of contact between liquid water and the soil, forming a distinct population in the soil. However, the team found no such marker.
The team also discovered further evidence to support the idea that Martian soil has been largely dry throughout its history by comparing soil data from Mars, Earth and the Moon. The researchers deduced that the soil was being formed in a similar way on Mars and the Moon because they were able to match the distribution of soil particle sizes.
On Mars, the team inferred that physical weathering by the wind as well as meteorites breaks down the soil into smaller particles. On the Moon, meteorite impacts break down rocks into soil, as there is no liquid water or atmosphere to wear down the particles.