Washington, Nov 18 : An international team of scientists has uncovered evidence that supports the idea that oceans once covered about a third of ancient Mars.
The scientists found the evidence by analyzing data from the Gamma Ray Spectrometer onboard NASA's Mars Odyssey.
"We compared Gamma Ray Spectrometer data on potassium, thorium and iron above and below a shoreline believed to mark an ancient ocean that covered a third of Mars' surface, and an inner shoreline believed to mark a younger, smaller ocean," said University of Arizona (UA) planetary geologist James M. Dohm, who led the international investigation.
"Our investigation posed the question, Might we see a greater concentration of these elements within the ancient shorelines because water and rock containing the elements moved from the highlands to the lowlands, where they eventually ponded as large water bodies?" Dohm said.
Mars Odyssey's GRS, or Gamma Ray Spectrometer, led by William Boynton of UA's Lunar and Planetary Laboratory, has the unique ability to detect elements buried as much as 1/3 meter, or 13 inches, below the surface by the gamma rays they emit.
That capability led to GRS' dramatic 2002 discovery of water-ice near the surface throughout much of high-latitude Mars.
Results from Mars Odyssey and other spacecraft suggest that past watery conditions likely leached, transported and concentrated such elements as potassium, thorium and iron.
"The regions below and above the two shoreline boundaries are like cookie cutouts that can be compared to the regions above the boundaries, as well as the total region," Dohm said.
The younger, inner shoreline is evidence that an ocean about 10 times the size of the Mediterranean Sea, or about the size of North America, existed on the northern plains of Mars a few billion years ago.
The larger, more ancient shoreline that covered a third of Mars held an ocean about 20 times the size of the Mediterranean, the researchers estimate.
According to the scientists, the potassium-thorium-iron enriched areas occur below the older and younger paleo-ocean boundaries with respect to the entire region.
The scientists used data from Mars Global Surveyor's laser altimeter for topographic maps of the regions in their study.
"The GRS adds key information to the long-standing oceans-on-Mars controversy," Dohm said.
"But, the debate is likely to continue well into the future, perhaps even when scientists can finally walk the Martian surface with instruments in hand, with a network of smarter spaceborne, airborne and ground-based robotic systems in their midst," he added.