**火星岩石中发现氮元素**
美国太空研究人员说，他们发现更多证据显示火星可能曾经存在能够维持生命的环境。
美国航空航天局的科学家们星期二说，火星探测器“好奇号”在火星岩石中发现了硝酸盐。硝酸盐中含有氮，而氮是维持生命的必要元素。
但科学家们说，没有证据显示火星上的氮来自生物，并强调火星表面不能维持任何形式的生命。
科学家们相信，火星上的硝酸盐存在已久，很可能来自流星或闪电。
目前还没有迹象显示火星可能曾经适于居住。过去发现，火星表面曾被淡水覆盖。
Ancient Nitrogen, a Key Element for Life, Found on Mars
U.S. space researchers say they have found more evidence that the planet Mars could have once been able to support life.
NASA scientists said Tuesday the Curiosity Mars rover found nitrates in Martian rocks. Nitrates are compounds that contain nitrogen, an element essential for life.
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.
They believe the nitrates are ancient and probably came from meteorites or lightning strikes.
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.
**也门总统哈迪逃离亚丁官邸**
也门官员说，哈迪总统星期三逃离南部城市亚丁的官邸，目前在该城市内某个地方。胡赛反政府武装正在继续向南部推进。
也门官员否认了有关哈迪总统已经离开亚丁的报道。 哈迪上个月在首都萨那摆脱胡赛反政府武装的软禁，逃到海湾城市亚丁，试图建立自己的政府。从那时起，亚丁一直是哈迪的避难地。
胡塞反政府武装去年9月占领萨那，目前正向南部的亚丁推进。哈迪逃离亚丁的报道出现之前，反政府武装与亲哈迪的军队发生冲突，控制了亚丁以北60公里处的埃尔-阿纳德空军基地。
埃尔-阿纳德基地是美国军事人员发动无人机攻击行动的重要情报基地，无人机攻击行动的目标是设在也门的阿拉伯半岛基地组织。美国上星期六宣布，由于也门安全局势恶化，决定撤走所有驻也门人员。
哈迪星期二呼吁联合国安理会授权军事干预，制止胡塞反政府武装的攻势。
Yemeni President Flees Palace as Houthis Advance South
Yemeni officials said President Abd-Rabbu Mansour Hadi fled his palace in the southern city of Aden for an undisclosed location in the city Wednesday as Houthi fighters continued their advance to the south.
The officials denied earlier reports that Mr. Hadi had left the city entirely. Aden has been a refuge for Mr. Hadi since last month, when he escaped house arrest by the Houthis in the capital, Sana'a, and went to the city on the Gulf of Aden to try to establish his government there.
The Houthis captured Sana'a last September and have been advancing south toward Aden. The reports that Mr. Hadi had fled came after the rebels took control of the key Al-Anad airbase about 60 kilometers north of the city following clashes with pro-Hadi forces.
Al-Anad was an important intelligence site used by U.S. personnel in the drone campaign targeting militants from the Yemen-based al-Qaida in the Arabian Peninsula. The U.S. announced Saturday that all of its remaining personnel had left the country because of the deteriorating security situation.
Mr. Hadi appealed to the U.N. Security Council on Tuesday to authorize a military intervention to halt the Houthi advance.