Mars meteorite was briefly drenched in water
Sen—A little over a century ago, residents of Nakhla, a town in Egypt, were startled by a sudden shower of stones from the sky. Unlike shooting stars, which are usually comet dust, these were chunks of rock, the remains of a larger object that broke up in the atmosphere.
Legend has it that one of the fragments killed a dog. But the most incredible fact about this shower of 1911 is that it was later discovered that the meteorites were from Mars.
You may wonder how anyone can tell this. The answer is that air found trapped inside the meteorites was analysed and found to be a match for the atmosphere of the Red Planet. It is thought that an asteroid that struck Mars around ten million years ago creating an explosion that melted surrounding rock and flung it into space. And after aeons floating in orbit around the Sun, some of this debris fell to Earth.
There are a handful of meteorites found around the world that have been shown to be from Mars. The most recent fell in the Sahara Desert near Tissint, Morocco, in July 2011. They are invaluable to planetary scientists because they give them the chance to investigate our neighbour in space without the expense of having to go there.
One labelled ALH84001 that was found in the Antarctic sparked controversy in 1998 when some NASA scientists said they thought it contained fossilised microbes.
That finding is now generally considered not proved. But in 1996 the NASA team went further and claimed to have also found evidence of alien life in a chunk of Nakhla that is kept London's Natural History Museum. Again there is general skepticism.
Now a new finding has been announced about one of London's Nakhla samples that is far less controversial but instead a step forward in understanding the former environment on Mars.
A chunk of the Nakhla meteorite held at London's Natural History Museum. Credit: NHM
Scientists at the University of Glasgow, working with the Scottish Universities Environmental Research Centre, have found the first evidence yet of water dissolving the surface of Mars.
Previous research on meteorite fragments provided evidence that there was once water on Mars through the presence in the meteorite of 'secondary minerals' – types of carbonates, hydrous silicates and sulphates that probably formed when Martian minerals reacted with liquid water.
Professor Martin Lee of the University's School of Geographical and Earth Sciences is lead author of a paper in the Meteoritical Society's journal MAPS. He said: "What has been unclear in the past is exactly where the chemical elements which made up the secondary minerals within Nakhla came from.
"Using a scanning electron microscope, we examined many tiny bowl-shaped depressions, known as etch pits, in grains of the minerals olivine and augite found in the meteorite.
"What we've found for the first time is evidence that the etch pits were created when water dissolved the olivine and augite, and that the elements released from those minerals led to the formation of the secondary minerals.
"It's an exciting discovery and better informs our understanding of how water affected rock on Mars."
Interestingly the amount of dissolution found suggests the area of Mars that supplied the Nakhla meteorites was under water for less than a year. Other evidence has suggested that large oceans covered regions of Mars in the more distant past.
Of the new study, Professor Lee said: "That's certainly not long enough to sustain a life-supporting biosphere. However, the findings of our study are from a tiny piece of a very small chunk of the surface of Mars, so it's difficult to draw any large-scale conclusions about the presence of water on the planet or its implications for life."