space trip

Why is NASA sending 5,000 water bears and 128 squid to space?

Spoiler alert: Some aren’t making it back alive.

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As if the world wasn’t big enough for microscopic animals, the tiniest of creatures are taking on even bigger frontiers in space.

On June 3, SpaceX is launching its 22nd cargo resupply mission to the International Space Station (ISS). While the cargo includes equipment for ongoing experiments and new solar panels, it also has a few passengers: 5,000 tardigrades, also known as water bears, and 128 baby glow-in-the-dark bobtail squid.

These tiny animals are venturing out into space for good reason: helping researchers understand the effects of spaceflight on the human body. This type of research has gotten more crucial as space agencies target further destinations such as Mars for the future of space travel.

NASA's Human Research Program relies on the astronauts on the ISS for studies on how the human body adapts to time spent in a microgravity environment and whether the effects of being in space can cause permanent damage to human beings.

Only around 240 astronauts and cosmonauts have traveled to the ISS. Some stayed in space just for a few weeks or months, but astronauts Peggy Whitson and Mark Kelly stayed for almost a year. As more humans go into space and come back to Earth, their stays have changed how scientists understand the effects of spaceflight on the human body but they still form a rather small pool of research subjects.

In order to make up for the small human sample size — and perform experiments that would otherwise endanger human subjects — scientists deploy animal test subjects, especially ones that can easily stow away in a cargo resupply because of their small size. This includes one of the hardiest of all: the tardigrade.

Why is NASA sending 5,000 tardigrades to the ISS?

In April 2019, the Israeli Beresheet spacecraft crash-landed on the Moon while carrying several thousand dehydrated tardigrades on board.

The microscopic creatures, nicknamed “water bears” for their resemblance to tiny, swimming bears, were sandwiched between micron-thin sheets of nickel and suspended in epoxy, a resin-like preservative that acts like a jelly. Some scientists believe that they may have survived the landing because tardigrades are known to survive under extremely harsh conditions.

Tardigrades are returning to space, this time to test just how their tiny bodies adapt to the harsh environment.


In September 2007, two species of dehydrated tardigrades were exposed to the vacuum of space and solar radiation onboard NASA’s Foton-M3 mission. The water bears were brought back to Earth and rehydrated, and surprisingly survived as though nothing had happened with some of them even reproducing afterward.

Their unmatched survival skills make them ideal candidates for testing just how much radiation and other extreme space conditions a living organism can handle.

Thomas Boothby, assistant professor of molecular biology at the University of Wyoming and principal investigator, lists some of the conditions that tardigrades can survive, including:

  • Being dried out.
  • Being frozen.
  • Being heated past the boiling point of water.
  • Being exposed to thousands of times more radiation than humans can endure.

“Our main objective is to identify changes at the level of gene expression that are going on in these really tough, robust animals when they're exposed to the rigors of spaceflight,” Boothby said during a press conference on Wednesday.

The tardigrades will be frozen for delivery to the ISS, then thawed out, revived, and grown in a special bioculture system. Some of the tardigrades will be exposed to the radiation of space for a week, while others will be exposed for a longer period of time to test the short and long-term effects of spaceflight.

The researchers will then observe what genes are being turned on or off to help the tardigrades survive in this environment.

“If we see that tardigrades are producing a lot of antioxidants,” Boothby says. “That might give us insights into how we could safeguard humans, for example, by supplementing their diet with foods with increased levels of antioxidants.”

Why 128 squid will die on the ISS

Along with the tardigrades, NASA is sending up a small cephalopod: the bobtail squid. Unlike their more massive cousins, they only grow to the size of an average human thumb.

These baby squid are booking a one way ticket to space.

Aleksei Permiakov/Moment/Getty Images

The squid were chosen for two big reasons:

  • They have a special light organ that can be colonized by a species of luminescent bacteria, which they use to glow in the dark. This makes the process easy to follow because it’s a single species of bacteria and one type of host tissue.
  • They also have an immune system that is surprisingly similar to that of humans.

Jamie Foster, professor in the Department of Microbiology and Cell Science at the University of Florida and principal investigator of the squid experiment on the ISS, is interested in how microbes communicate with animal tissues in space.

“As astronauts go and explore space, they're taking with them a capacity of different microbial species,” Foster said during the Wednesday press conference. “It's really important to understand how those microbes are changing in the space environment and how those relationships are established.”

The squids’ immune system provides a parallel to how the human immune system is responding to the microbes in space.

The experiment will launch 128 baby squid into space, placed in bags of seawater. As bacteria are added to the water, the researchers will observe what happens within the first few hours of the initial stages of colonization by bacteria.

Unfortunately for the squids, it’s going to be a one-way ticket to space as they will have their tissues frozen and will return back to Earth as tiny corpses to conduct follow-up observations in labs on the ground.

But in the process, both the squid and the tardigrade will serve a higher purpose: helping humans learn about how well we might fare as space explorers on long-duration missions to Mars and beyond.

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