Meteorites blasted from the surface of Mars when an asteroid hit the Red Planet 11 million years ago reveal that there was once running water below the surface.
A group of these meteorites fell to Earth in 1911. They were named the nakhlites after El Nakhla in Egypt where the first of them fell.
Now planetary scientists at the University of Glasgow have used a new technique to analyse these nakhlites, and claim they shed light on the process which generated liquid water on Mars.
"There's a huge amount of information about Mars locked inside the little pieces of the red planet which have fallen to Earth as meteorites," said Dr Luke Daly, Research Associate in Solar System Science at the University of Glasgow’s School of Geographical and Earth Sciences.
"What we've seen is that the pattern of deformation in the minerals matches exactly the distribution of weathering veins that formed from the Martian fluids."
The analysis reveals that the Martian space rocks were hit by not one but two asteroids – the first 633 million years ago and the second about 11 million years ago.
The first asteroid formed a massive impact crater in the volcanic rock on the Martian surface.
"This impact was big enough and hot enough to melt the ice under the Martian surface and send it rushing through newly-formed cracks in the rock – effectively forming a temporary hydrothermal system below the surface of Mars, which altered the composition of the minerals in the rocks, close to these cracks," said Dr Daly.
"It suggests an asteroid impact was the mystery mechanism for generating liquid water in the nakhlites long after the volcano that formed them on Mars had become extinct."
The second asteroid impact, hundreds of millions of years later, "had the right combination of angle and force to blast the rocks off the surface of the planet and begin their long journey through space towards Earth".
The team believe that their findings provide new insight into the formation of the Martian landscape.
Regular asteroid bombardments could have had similar effects on underground ice throughout the course of Martianhistory, creating temporary hydrothermal systems all over the planet and important sources of liquid water.
Their analysis also provides important clues which could help pinpoint exactly where on Mars the nakhlites originated.
"We're currently trying to understand Martian geology through these meteorites without knowing what part of Mars' surface these so-called nakhlites came from.
"Our new findings tightly constrain the possible origins of the nakhlites – we now know that we're looking for a complex volcanic edifice, about 1.3-1.4 billion years old, with one crater around 633 million years old and another one about 11 million years old.
"Very few places on Mars could fit that bill.
"It's a piece of interplanetary detective work which is still ongoing but we’re keen to crack the case."
The researchers, from the University of Glasgow, Leeds University, Uppsala University, Oxford Instruments Nanoanalysis, Università di Pisa, the University of New South Wales, and Curtin University, looked at samples from two nakhlites.
One, known as "Miller Range 03346", was found and recovered from the Miller range mountains in Antarctica in 2003 by the Antarctic Search for Meteorites expedition.
The second, ‘Lafayette’, was found in Purdue University’s collection of rock samples in 1931.
They used used a technique known as electron backscatter diffraction to analyse the nakhlites.
The research, funded by the Science and Technology Facilities Council (STFC), was published today in Science Advances.
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