这是外星生命么？嘿，可能不是哟！但在所有的地球生物中，缓步动物水熊虫可能是最佳候选人，这是因为水熊虫在缺乏食物与水源的环境下能存活数十年，在温度从接近绝对零度到超过水的沸点时都能生存，在压力从接近真空到海底高压时还能生存，即便是直接暴露在危险的辐射下也照样能够生存。2011年，人们把这些嗜极生物用太空飞船送入外太空测试其生存范围，结果是水熊虫存活最久，部分原因是它们能自我修复DNA并且能把身体中的水份含量降低到几个百分点。最近，当一些微型水熊虫搭载俄罗斯“火卫一咕噜”探测器前往火卫一的时候，差点就变成了外星生命，可惜火箭发射失败，太空舱滞留在地球轨道上，它们仍还是地球生物。地球上的水熊虫比人类还要普遍。上图是一张经过色彩增强的电子显微镜图片，一只1毫米长的水熊虫正在苔藓上爬行。
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Explanation: Is this an alien? Probably not, but of all the animals on Earth, the tardigrade might be the best candidate. That's because tardigrades are known to be able to go for decades without food or water, to survive temperatures from near absolute zero to well above the boiling point of water, to survive pressures from near zero to well above that on ocean floors, and to survive direct exposure to dangerous radiations. The far-ranging survivability of theseextremophiles was tested in 2011 outside an orbiting space shuttle. Tardigrades are so durable partly because they can repair their own DNA and reduce their body water content to a few percent. Some of these miniature water-bears almost became extraterrestrials recently when they were launched toward to the Martian moon Phobos on board the Russian mission Fobos-Grunt, but stayed terrestrial when a rocket failed and the capsule remained in Earth orbit.Tardigrades are more common than humans across most of the Earth. Pictured above in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss.
每日天文一图（APOD）是美国宇航局天体物理学部每日定期发布的天文图片，并配有专业的简短解释，是小子时常光顾的地方，地址为：http://apod.nasa.gov/apod/。现将部分酷图转来并对原文解释做了翻译，英文及天文知识均有限，译错之处敬请各位指正。
秋天的麦兜 2013年3月6日 于济南。
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