Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2023 May 21
An usual looking creature is pictured which may appear
alien but is actually a Earth-dwelling tardigrade. The 
tardigrade has no apparent eyes, a light brown body,
a circular gear-like snout, and claws at the end of its
numerous feet. The tardigrade is seen perched on green moss.
Please see the explanation for more detailed information.

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.

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Tomorrow's picture: sea blue sky


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