苔藓上的水熊虫

2023年5月21日

Tardigrade in Moss
Image Credit & Copyright: Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images

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 these extremophiles 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 in 2011 when they were launched toward to the Martian moon Phobos, and again in 2021 when they were launched toward Earth’s own moon, but the former launch failed, and the latter landing crashed. Tardigrades are more common than humans across most of the Earth. Pictured here in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss.

Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)

Tomorrow’s picture: pinwheel supernova

苔藓上的水熊虫
影像提供与版权: Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images

说明: 这是外星生物吗？或许不是，然而在地球的所有生物中，水熊虫可能是最好的候选。因为水熊虫能长达数十年不吃不喝，在接近绝对零度或远高于水沸点的环境中能活，于接近真空到远高于海床压力的环境也活得下来，甚至直接曝晒在危险幅射环境中也不会丧命。2011年，这些嗜极生物被放在轨道上的太空梭外头之太空环境中，以测试它的生存范围到底有多广。水熊虫能这么耐命，部分原因是因为它们能修补自身的DNA，以及能将自身的水分降低到只有几个百分点。这种微小的水熊虫在2011年差点真的成为外星生物，当时它们被装在火卫一探测器上并发射前往火卫一，然后在2021年，它们又成为月球探测船的乘客；不过前者发射失败，而后者则在降落时坠毁。在地球的大部分区域，水熊虫是比人类更常见的生物。在这张色彩经过强化的电子显微镜照片里，一只1毫米长的水熊虫正在苔藓上爬行。 (tardigrade 水熊虫、缓步动物)

您的天空惊喜: APOD在你生日那天拍了什么照片？（1995年后）

明日的图片: pinwheel supernova