[2016·河北保定摸底考试]Mars (火星) appears to be flowing with small streams of salty water, at least in the summer, scientists reported Monday. “It suggests that it would be possible for there to be life today on Mars，” NASA's science mission chief, John Grunsfeld,

　　said at a news conference on September 28, 2015.

　　The streams are about 12 to 15 feet wide and 300 feet or more long, scientists said. “What

　　we're dealing withP1 is wet soil, thin layers of wet soil, not standing water，” said Alfred McEwen of the University of Arizona at Tucson, the principal scientist for the Mars Reconnaissance Orbiter's high－resolution imaging experiment.

　　Because liquid water is essentialW1 to life, the findings could have major implications for the possibility of Martian life. The researchers said further exploration is needed to determine whether microscopic life existsW2 on the planet.

　　The presence of liquid water could also make life easier for astronauts visiting or living on Mars. Water could be used for drinking and for creating oxygen and rocket fuel. NASA's goal is to send humans there in the 2030s.S

　　The evidenceW3 of flowing water consists largely ofP2 dark, narrow streaks (条痕) on the surface that tend to appear and grow during the warmest Martian months and fade the rest of the year.

　　Mars is extremely cold even in summer, and the streaks are in places where the temperature is as low as minus 10 degrees Fahrenheit. But salt can lower the freezingW4 point of water and melt ice.

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