Gas trapped in meteorite could help scientists reconstruct conditions on Mars when the rock was blasted into space

A lump of space rock that shattered the predawn calm of the Moroccan desert with a fireball and double sonic boom last year was knocked off Mars in a cosmic collision roughly 700,000 years ago.

The date of the Martian impact means the rock was flung into space and began its journey to Earth when the shared ancestor of modern humans and Neanderthals was still alive and well in Africa.

Scientists dated the collision through a fresh analysis of the remains of the meteorite, based on the exposure of its elements to intense cosmic rays during its journey through space.

The Tissint meteorite, as it is known, is particularly valuable because it was recovered before it had suffered any weathering on Earth.

Witnesses said it split in two as it fell to Earth and landed in the desert near Tata, south-east Morocco, at 2am local time on 18 July last year. Pieces weighing between 100g and 2kg have been recovered, along with thousands of smaller fragments. The intact meteorite is estimated to have weighed 17kg.

Researchers at the Hassan II University of Casablanca found regions of black glass inside the meteorite that are thought to contain gas, rock and traces of Martian soil. "What is really exciting in this meteorite is that it has this black glass trapped inside," said Hasnaa Chennaoui Aoudjehane, who worked on the specimen.

Further analysis of the glass and the gas locked up in its tiny bubbles may help scientists reconstruct the conditions on Mars when the rock was blasted into space.

"Those bubbles are interesting because they trapped Martian conditions at the moment the meteorite formed, and it hasn't had any exchange with other materials," Chennaoui Aoudjehane said.

The research appears in the latest issue of Science. © Guardian News and Media 2012