Distinctivefractures in ancient lava flows on Mars suggest that water occasionally floodedportions of the planet?s surface. The research piles onto previous findings thatsuggest the same.
Thefractures, called columnar joints, are the first that have been observed on aplanet other than Earth.
"Columnarjoints form as cooling lava contracts," said Moses Milazzo, a geophysicistwith the U.S. Geological Survey in Flagstaff, Ariz.
Thecharacteristics of the column-like fractures can help scientists understand therole ofwater in geologic processes on Mars. Milazzo worked with the NASA Mars ReconnaissanceOrbiter HiRISE camera team to make the finding, which is detailed in thejournal Geology.
The Martiancolumns, about 3 feet (1 meter) in diameter and about 100 feet (30 meters)high, were identified in the tilted inner walls of an impact crater.
"TheHiRISE instrument just barely has the resolution to pick out the columns ifthey're facing the camera with the perfect orientation," said Milazzo.When the impact crater formed, the rocks were tilted backward, toward the sky,which is what allowed the identification.
The impactcrater where the columns were discovered is in a region that has a history ofextensive volcanic activity. Milazzo suspects that the columnar joints formedas lava flows were episodically flooded by liquid water, which quickly cooledthe lava. Flooding cycles may have lasted from a few months to a few years,they estimate.
On Earth,columnar joints are common in the rocks of the Colorado Plateau, which providea study site for comparisons to Mars.
Othergeological evidence on Mars points to periods when floods washed across thesurface, including similarities of certain canyons to Idaho'sBox Canyon and modelingstudies that suggest some areas were inundated for at least 10,000 years.
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