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The first interstellar travellers from Earth may be a species that is no stranger to space exploration: tardigrades. These creatures grow only 0.5 millimetres long but are some of the most resilient animals known to science, even surviving in the vacuum of space.

Until now, only five craft have left our solar system and none of them has carried biological life. It currently takes decades for craft to travel the 18 billion kilometres to interstellar space, but a is developing solar sail propulsion, boosted by Earth-based lasers, that could eliminate the need for conventional rocket propellant and cover the same distance in just days.

While previous long-distance craft have only included messages, like the Voyager Golden Records, making it easier to leave the solar system opens the door to experimenting with live organisms.聽 at the University of Florida and his colleagues analysed how much food would be needed to keep various species alive, how much they weigh and their resilience to the levels of radiation and high acceleration that would be encountered on their journeys. Tardigrades come out as a good option for low-maintenance pioneering interstellar travellers.

鈥淚t would be nice to send humans, but there are some biological constraints that would make it more favourable for us to send other organisms at least in the first few flights,鈥� he says. 鈥淚t takes a lot of energy to send anything out into interstellar space, at least at the speeds that we鈥檙e proposing, and in order to do that you need a really small payload.鈥� Unfortunately, such a flight would be a one-way mission, he says.

Tardigrades and the tiny worm Caenorhabditis elegans, another species in contention, both have the benefit of being capable of cryptobiosis, a form of extreme hibernation in which the animals radically slow their metabolism when in adverse conditions such as desiccation or freezing. Tardigrades are thought to use just 0.01 per cent of their normal energy when in cryptobiosis. They have already been shown to survive space flight and even exposure to the vacuum of space on prior missions, and may have .

at the University of Wyoming says tardigrades have 鈥渞emarkable鈥� resilience compared with almost all animals, but that interstellar travel is much more extreme than low Earth orbit.

鈥淚 think there would be a lot of things we could learn from tardigrades that would inform how we humans might fare. A major takeaway from this type of experiment would probably be identifying tricks tardigrades use to help them survive and using these tricks to try to develop therapies or countermeasures for humans faced with the stresses of interstellar travel,鈥� he says.

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