Life probably does not exist on Mars as there is no water on the surface of the planet, a new study found.
Water is vital for life, but a new study of meteorites that have crashed into the surface of the Red Planet over millions of years found none showed signs of rust.
And what moisture may exist is less than the driest place on Earth - the Atacama Desert in Chile and Peru which has no glaciers to feed it water so very little life can survive.
Some weather stations in this region have received no rain for years, while another station reports an average of one millimetre per year.
The international team of planetary scientists led by the University of Stirling suggested rust free meteorites showed Mars was incredibly dry, and has been for millions of years.
The findings showed how difficult it would be for life to exist on Mars today as Earth's nearest neighbour is the primary target in the search for life elsewhere.
Dr Christian Schr der said: "Evidence shows that more than three billion years ago Mars was wet and habitable.
"However, this latest research reaffirms just how dry the environment is today.
"For life to exist in the areas we investigated, it would need to find pockets far beneath the surface, located away from the dryness and radiation present on the ground."
A study last year using data from the Curiosity Rover investigating Gale crater suggested very salty liquid water might be able to condense in the top layers of Martian soil overnight
But the lecturer in environmental science and planetary exploration and science team collaborator for the Mars Exploration Rover Opportunity mission added: "But, as our data show, this moisture is much less than the moisture present even in the driest places on Earth."
The Mars Exploration Rover Opportunity provided data on a cluster of meteorites at Meridiani Planum - a plain just south of the planet's equator and at a similar latitude to Gale crater.
Dr Schr der for the first time calculated a chemical weathering rate for Mars, in this case how long it takes for rust to form from the metallic iron present in meteorites.
This chemical weathering process depends on the presence of water and takes at least 10 and possibly up to 10,000 times longer on Mars to reach the same levels of rust formation than in the driest deserts on Earth.