U.S. space researchers say they have found more evidence that the planet Mars could have once been able to support life.美国太空研究人员说道，他们找到更加多证据表明火星有可能曾多次不存在需要保持生命的环境。NASA scientists said Tuesday the Curiosity Mars rover found nitrates in Martian rocks. Nitrates are compounds that contain nitrogen, an element essential for life.美国航空航天局的科学家们星期二说道，火星探测器“奇怪号”在火星岩石中找到了硝酸盐。

硝酸盐中所含氮，而氮是保持生命的适当元素。But the scientists say there is no evidence the nitrogen came from living things and stress that the Martian surface cannot support any forms of life.但科学家们说道，没证据表明火星上的氮来自生物，并特别强调火星表面无法保持任何形式的生命。

They believe the nitrates are ancient and probably came from meteorites or lightning strikes.科学家们坚信，火星上的硝酸盐不存在已幸，很有可能来自流星或雷电。This is not the first sign that the planet may have at one time been habitable. Past discoveries show signs that fresh water once covered the Martian surface.目前还没迹象表明火星有可能曾多次适合于居住于。

过去找到，火星表面曾被淡水覆盖面积。

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