The Mars rover Opportunity has now solved the key puzzle it was sent to the Meridiani Planum to figure out: where is the hematite that was spotted in the area by the Mars Global Surveyor orbiter? The answer is in the "blueberries", the tiny mineral spheres that litter the rover's landing site.
The question was a key one, because hematite almost always forms in water, and water is thought to be a pre-requisite for life. Scientists led by Arizona State University's Phil Christensen revealed their discovery at the Lunar and Planetary Sciences Conference in Houston, Texas, on Tuesday.
Finding the hematite in the spheres makes sense, because earlier data from the rover showed the spheres are almost certainly concretions formed when water deposited layer after layer of minerals around a minute grain of sand.
Ever since it landed in January, Opportunity has been seeing more and more of the spheres, covering the soil, embedded in the bedrock, and seemingly strewn across the flat plateau surrounding the landing crater.
However, until now, nobody knew what they were made of. This was because at a few millimetres across they are far too small to fill the field of view of any of the rover's three spectrometers.
Berry bowl
The challenge was to find a place where the spheres were sufficiently concentrated to provide a target for the spectrometers. A "berry bowl" provided the solution, a shallow depression in the bedrock where dozens of spheres had collected in a tight bunch.
All three rover instruments, the mini-TES, Mossbauer, and Alpha Proton X-ray Spectrometers, as well as its microscope, were used on Saturday and Sunday to gather data and provided the definitive evidence.
The surrounding bedrock showed no sign of hematite at all, while the concentrated berries showed a very strong signal. It is now clear that, while not pure hematite, the spheres contain the primary concentrations of the mineral.
They can account for the hematite seen on the soil surface, because they are strewn across it, and for its absence in the bounce marks made by the rover's landing, because pictures show that all the spheres were driven into the soil and out of sight by the force of impact.
 |
||||||||||||||||||||
 |
|
|||||||||||||||||||
|
Subscribe to New Scientist for more news and features
|
||||||||||||||||||||
|
||||||||||||||||||||
Lost lakes?
There is one remaining question about the hematite, however. It appears to be even more concentrated on the plains outside the crater. Does that mean that there may be an additional source as well, perhaps an overlying layer of rock, or just that the plain is strewn with many millions of spheres?
Opportunity is expected to drive out onto that plain in a week or two, and should have a chance to answer that question as well.
Christensen, who designed the mini-TES, is hopeful that additional hematite-rich formations may be found that might prove the presence not just of water, but of large bodies of standing water that may have persisted for long periods.
David L Chandler, Houston
