BY DR EMILY BALDWIN
Posted: 20 March, 2009
According to new analysis of an eroded crater, a large scale depositional process has been at work in the equatorial regions of Mars that has implications for the climatic history of the planet.
The evidence comes from a Mars Express study of the mineralogical composition of the Aram Chaos region, a crater 280 kilometres in diameter lying almost directly on the Martian equator. The OMEGA instrument data shows a significant amount of sulphates and ferric oxides, the latter of which is more commonly known as rust, and which gives Mars its red tone.
The Aram Chaos region of Mars, a crater 280 km in diameter, where OMEGA detected large-scale deposits of ferric oxides. The inset shows the region in relation to other areas where the same minerals have been detected. Image: NASA/MGS/MOLA/THEMIS.
Although ferric oxide is common across the red planet, in the dark deposits of Aram Chaos there is a four-fold increase in the spectral signature of ferric oxides, which means that some process has concentrated the oxides in this location. Ferric oxides are generally found with sulphates but, in this case, the lighter sulphates have been blown away, leaving the ferric oxides exposed.
“They have accumulated in dark deposits at the bottom of sulphate cliffs,” says Stephane Le Mouelic, Universite de Nantes. The scientists say that this implies that the ferric oxides have been uncovered by erosion before dropping to the base of the cliffs. The dunes in this region are also enriched in ferric oxides.
While an interesting discovery for this region of Mars, the phenomenon is not exclusive to Aram Chaos. NASA’s Opportunity rover discovered ferric oxide deposits - nicknamed blueberries - one thousand kilometres away in Meridiani Planum. In addition, Valles Marineris, 3000 kilometres away, also shows similar deposits. The new detection of a similar chemistry in Aram Chaos therefore links together widely separated areas of Mars, and the scientists suspect there could be even more examples in other locations.
Mars Express has been orbiting the red planet for over five years. Image: ESA/Medialab.
“OMEGA is sensitive to the first hundreds of microns of the surface. So, a layer of Martian dust just one millimetre thick will hide the signature from us,” says Marion Masse, lead author on the paper describing these results. Thanks to wind erosion, which has occurred at Aram Chaos, the dust cover has been swept away to reveal the composition of the underlying rocks.
For the time being, however, the true extent and nature of the accumulation process remains a mystery. The science team are now exploring different mechanisms that could have caused it, from atmospheric precipitation such as rain or snow, to volcanic ashes or glacial deposits. Whatever the conclusion, the results will contribute to scientist's understanding of the past climatic and surface process that have shaped the planet.
The findings are discussed in the Journal of Geophysical Research.