At www.jpl.nasa.gov/news/news.php?release=2012-290&cid=release_2012-290 … the NASA Opportunity rover, not to be confused with the Curiosity rover now being set loose on the surface of Mars, has returned an image of spherical objects that differ from so called 'blueberries' (iron rich spherules) found in 2004. The new spherules were found on the rim of Endeavour crater and are just 3mm in diameter – and lack iron. Such concretions are thought to form in a wet environment – unlike cold and dry present day Mars. How they form may have to be re-evaluated – in fact, a geological puzzle.
At http://phys.org/print266751510.html … some scientists are thinking early Mars may never have been wet or warm and others think it once had a larger and more dense atmosphere that supported liquid water on the surface. They speculate that Mars may have or had, microbial life. What might have caused Mars to lose its atmosphere is unknown but one idea is that it was due to energetic particles (the solar wind).
Over at http://phys.org/print266655792.html … Mars appears to have clay minerals – yet to be examined by the Opportunity rover (or by the Curiosity rover) but generall considered an indicator of a wet environment (at least as far as alternative ideas have not been able to gather any momentum). In Nature Geoscience we have another take on the clay – even before it is examined by the rovers. A paper suggests the clays may have precipitated directly from scalding hot magma rather than from water washed rocks or water flowing in subsurface hydrothermal vents.