Tiny invertebrates are the first animals to withstand the vacuum and radiation of space.
It's one small step for water bears, one giant leap for animal-kind. Tiny animals called tardigrades — better known as water-bears — have become the first animals to survive the cruel vacuum, intense cold and radiation of space without a spacesuit.
Water bears were already known to be among the toughest critters alive. When not flying in a low Earth orbit, they prefer to spend their days in water, perhaps on a beach or a dewy patch of moss. But when the water dries up, the millimetre-long 'bears' can contract into a dried-out state and survive like that for years. They are also one of the few animals that survive year-round on continental Antarctica, and are among the most radiation-resistant animals known.
So if any animal on Earth could survive the rigours of space, Ingemar Jönsson, of Kristianstad University in Sweden, and her colleagues figured it would be the water bears. They loaded two species of tardigrade — Richtersius coronifer and Milnesium tardigradum, both already in their desiccated form — onto the European Space Agency's Biopan-6 experimental platform. The experiment was launched into orbit during the unmanned Russian Foton-M3 mission in September 2007.
For ten days, the tardigrades were exposed to the radiation, vacuum and low temperature of space. R. coronifer did not fare terribly well — none survived when exposed to the full spectrum of ultraviolet radiation, which can be extremely damaging to DNA. But three specimens of M. tardigradum did.
And when some wavelengths of ultraviolet light were filtered out (those shorter than 280 nanometres or longer than 400 nanometres), eggs laid by space-faring Milnesium tardigradum hatched just as well as controls that had not been exposed to space vacuum or ultraviolet radiation. The results are published this week by Current Biology1.
The results demonstrate just how resilient life on Earth can be, says Catharine Conley, NASA's acting Planetary Protection Officer. Before now, only lichens and bacteria had demonstrated their ability to survive both space vacuum and cosmic radiation.
And although tardigrades were clearly resistant to desiccation on Earth, the conditions in space are much more challenging. At sea level on Earth, air pressure is about 100,000 pascals; in low Earth orbit, it is more than a billion times lower. "Such low pressure imposes an extreme dehydration on cells," says Jönsson. "Not many water molecules can remain in the body under those conditions."
Some researchers want to understand how various Earth organisms might survive interplanetary flight, as a way of gauging whether life could have spread from one planet to another. As Planetary Protection Officer, Conley's mission is to understand which organisms might hitch-hike a ride on a spacecraft and contaminate other planets.
But she isn't too worried about the likelihood that tardigrades might catch a ride to Mars and set up shop. "Tardigrades, unfortunately, need stuff to eat," says Conley. "If you had to pick a single type of organism that would be likely to colonize Mars, it'd be a lichen, or maybe a photosynthesizing bacteria."
Jonsson, K. I. et al. Curr. Biol. 18, R1–R3 (2008).
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Ledford, H. Spacesuits optional for 'water bears'. Nature (2008). https://doi.org/10.1038/news.2008.1087