A new study suggests that dark markings on the planet Mars represent sand—not water. The research in 2015 suggested that lines on some Martian hills were evidence of water. Yet American scientists now say these lines appear more like dry flows of sand. If water is present, it is likely to be a small amount. Water in liquid form would be necessary for microbial(微生物的) life.
NASA, the American space agency, said more research is needed. Michael Meyer is the lead scientist for NASA's Mars exploration programme. He noted that the latest study does not reject the presence of water. But he admitted," It just may not be as exciting as the idea of rivers going down the sides of cliffs(悬崖). "
The new findings come from a team led by Colin Dundas of the United States Geological Survey. His team measured 151 of these lines in 10 areas. Most of the lines end with slopes between 28 degrees and 35 degrees. These measurements are similar to active sand dunes(沙丘) on both Mars and Earth. A small covering of dust that moves and sometimes becomes lighter might help explain the markings. They usually appear in the Martian summer time, and then disappear until the next year. If these lines are dry, this suggests that recent Mars has not had large volumes of liquid water. Dundas and his research team say that many questions remain.
"I still think that Mars has a great potential for having had life early in its history," Meyer said." As long as that's true, we also have a reasonable possibility of life still being on Mars. It just happens to be cryptic or well hidden."
NASA currently has no robotic vehicle—either on Mars or in development—with the ability to climb steep slopes. The lack of such equipment has engineers coming up with ideas like Martian helicopters or planes without pilots.
