How a few tiny lumps of rock travelled all the way from the surface of Mars to a laboratory in Leicester

At nine o’clock on the morning of 28 June 1911, a meteorite fell out of the sky above Egypt. By the time it reached the ground, it had shattered into about 40 stones, scattered over five sites around the village of El Nakhla. One version of events claims that one of the stones hit and killed a dog.

Seventy years later, it was first suggested that the unusual Nakhla meteorite could have originated on Mars and this was confirmed in 1983 when gas within the rock was found to match the atmospheric measurement taken by the Viking landers. Several other ‘nakhlites’ have been found and identified over the years.

Hitesh Changela, a PhD student in the University of Leicester’s Space Research Centre (part of the Department of Physics and Astronomy), was given access to five Nakhlites, including the 1911 rock, for his research. Tiny wafers of rock, about 0.1 microns thick (ie. one ten-thousandth of a millimetre), were shaved off the meteorites and examined by Hitesh using the University’s electron microscopes in Physics and Astronomy and the Advanced Microscopy Centre.

It is believed that these lumps of Martian rock were hurled into space by the impact of a large meteorite on the surface of Mars. However, an earlier impact created veins in the rock. At the same time, ice below the rock melted, depositing clay and carbonate minerals into the veins.

Hitesh’s research showed that the principal material within the veins are clay and an iron-magnesium-aluminium silicate in the form of a gel. Some of the meteorites contained traces of other elements and salts including potassium, chlorine, iron and gypsum (a form of calcium sulphate).

Studying the composition of these Martian meteorites is vital to understanding the geology of Mars, simply because they are the only direct contact humanity has had with the planet. Although several dozen spacecraft have been sent to Mars over the decades, few of the missions carried landers and some of those crashed or otherwise failed to work, leaving just six successful missions to the surface: Viking 1 and 2, Mars Pathfinder, Phoenix and the rovers Spirit and Opportunity.

"It is very exciting to be able to analyse rare samples of Mars in our labs at Leicester,” says Hitesh. “I think this is the best way to understand water on the red planet and the formation of clay and carbonate minerals recently identified by orbiting spacecraft."

Dr John Bridges, who supervised Hitesh’s PhD, agrees: “We are now starting to build a realistic model for how water deposited minerals formed on Mars, showing that impact heating was an important process. The constraints we are establishing about temperature, pH and duration of the hydrothermal action help us to better understand the evolution of the Mars surface.”

Source: Leicester university