探索神秘火星
多年以来,火星一直深深地吸引着我们。自从天文学家首次用望远镜观测这个星球,我们就开始了对火星上生命的遐想。火星 (mars) 是太阳系九大行星之一,按离太阳由近及远的顺序排列为第四。除金星以外,火星离地球最近。火星的自转周期(24小时39分22.6689秒)几乎与地球 (23小时56分4.09秒)一样;火星自转轴的倾角也几乎和地球相同。因而,火星也有四季变化,气温比地球低,生存条件仅次于地球。火星与地球明显不同 的是,火星的公转周期几乎是地球公转周期的两倍,迹象是导致生命起源的主要因素,因此火星是否存在生命一直是天文学家长期争议的论题。为了找到这一论题的 答案,人类对与地球相邻的火星表现了浓厚的兴趣。
人类探测火星历程
自20世纪60年代以来,对火星的空间探测不断获取新的发现。40多年来,苏联、美国、日本和欧洲共计划了30多次火星探测,其中三分之二以失败告终,但 研究一直没有排除火星上有生命存在的可能性。进入21世纪,火星是人类探索的新大陆。国际天文学界新世纪空间探测的第一个重头戏就是火星。
1962年11月苏联”火星1号” “火星1号”探测器在飞离地球1亿公里时与地面失去联系,从此下落不明,它被看作是人类火星探测的开端。
1965年7月15日美国”水手4号” “水手4号”飞近火星,从距离火星1万公里处拍摄了21幅照片,发现火星上存在大量环形山,火星大气密度只有地球的1%,火星既没有熔化的铁核也没有磁场。
1969年美国”水手5号”"水手6号” 它们拍摄的200多幅照片表明,火星表面的温度比预想的更低,火星大气中二氧化碳含量高达95%,水蒸气几乎难以寻觅。当年,美国水手7号探测器发回126张照片。
1972年5月美国”水手9号” 美国“水手9号”飞船沿火星外层空间轨道飞行,成为火星的第一颗人造卫星,环绕火星轨道进行长期考察。“水手9号”成功拍摄了火星全貌,发回7329张照片,确认火星上并不存在运河,火星的一个半球上有许多环行山,外貌很象月球,另一个半球则比较平坦。
1974年苏联“火星5号” 探测器环绕火星轨道飞行数天。同年,苏联“火星6号”和“火星7号”探测器在火星着陆,探测结果没有公布。
1975年美国“海盗1号” “海盗2号” “海盗1号”是人类发射的探测器第一次成功登陆火星。把火星探测活动推进了一步。
1989年-1996年多次失败 苏联“福波斯1号”和“福波斯2号”,美国“火星观察者”失踪,俄罗斯“火星—96”航天器 发射失败。
1996年12月4日美国”火星探路者号” 携带“旅居者”号火星车的美国“火星探路者”号探测器发射升空,“旅居者”号在地面工作人员的遥控下在火星上行驶,这次探测活动使人类对火星地表景观有了直观的认识。
2001年4月美国”奥德赛”号 发现火星表面和近地表层中可能有丰富的冰冻水,但这一问题仍存在争议。
2003年6月2日欧洲宇航局”火星快车” 2004年欧洲航天局宣布,发现火星南极存在冰冻水,这些冰冻水部分裸露在火星表面,没有被由二氧化碳凝固形成的干冰全部覆盖。这是人类首次直接在火星表面发现水。
2003年美国”勇气号”"机遇号” 搭载“火星探测流浪者”号探测器飞向太空。寻找那里是否有水的踪迹。7月”机遇”号火星升空。2004年”机遇”号火星车成功降落在预定着陆地点——火星“梅里迪亚尼平原”。
2008年美国”凤凰号” 在加热火星土壤样本时鉴别出有水蒸气产生,从而确认火星上有水存在。
火星地形
火星表面可以分为三大主要区域:南部高地、北部平原、以及极地地区。表面引力=3.72米/秒2,即地球引力的0.38倍。 表面温度=-140到20摄氏度(平均值=-63摄氏度) 。
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陨石坑疑似干涸湖泊 |
火星或有内部洞穴系统 |
北极区域沙丘地带 |
160公里宽的峡谷 |
直径达30公里的陨石坑 |
火星是否有水
火星上是否有水是一个很重要的问题,因为水是支持生命存在的基本条件,载人的火星探测器将需要水源,未来可能进行的火星地球化和移民将需要水。有迹象表明火星上曾经有过水流,而且现在可能仍然存在。
科学家已经在其大气中和两极冰盖下发现了水。绕火星飞行时,探测器发现了貌似河谷和水蚀的地质特征。此外,由于火星表面极其寒冷,因此可能有大量的水冻结储 存在火星表面以下。 2008年6月,“凤凰”号着陆探测器发回的一些照片显示,火星表面有白色物质,但在几天后消失。2008年7月,美国“凤凰”号着陆探测器项目小组 说,“凤凰”号在加热火星土壤样本时鉴别出有水蒸气产生,从而确认火星上有水。
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火星上是否有生命
海盗号探测器进行了一些有关生命过程的测试。例如在营养液中培养土壤样本,看是否有二氧化碳、甲烷和氧气等气体释放,因为细菌活动会产生这些气体。这些实验 和其他实验的结果似乎显示了火星土壤具有化学活性,但不具有生物活性。尽管这个干燥、寒冷的火星荒漠存在生命的机会渺茫,但生物学家最近却发现地球上类似 火星环境的地区(如南极洲)有细菌生存。
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人类对于这颗红色星球的探索从来都没有停止过,在未来,人类对它的探索也将继续。近日,美国宇航局计划将火星探测器与网络相连,网友利用绰号为 “HiWish”的在线工具,可以给火星勘测轨道飞行器(MRO)发出拍摄指令,当MRO轨道在合适的位置,就会拍下火星照片,从而让普通人通过有趣和互动的方式探索这个神奇的红色星球。对火星的探索,从高端的科学研究开始走向普通人的生活,因为人类相信,地球注定不会是孤单的。
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