If you grew up watching the kid’s television network Nickelodeon, chances are you understand that there are few honors in this world greater than being doused with the channel’s signature bright green slime. Last week, astronauts aboard the International Space Station (ISS) joined the illustrious ranks of the slimed, all in the name of science, according to a release.
Nickelodeon sent around two liters of their green goop into orbit in the summer of 2019 aboard SpaceX’s 18th commercial resupply mission. The Slime in Space project’s idea was to create an educational virtual field trip for teachers to use in class, but materials scientists were also tapped to guide astronauts through a series of experiments to learn more about how slime behaves in microgravity.
Researchers from Portland State University’s (PSU) mechanical and materials engineering department were excited to design the experiments for the unique project.
“We just went, ‘You’re kidding!’ They’re going to put slime in space,” Mark Weislogel, an engineer at PSU, tells Morgan Romero of local NBC affiliate KGW8. “That’s such a unique fluid, we would never want to miss the opportunity to study something like that.”
The project held special resonance for Weislogel’s fellow PSU engineer Rihana Mungin, who grew up watching Nickelodeon.
“I audibly squealed and was very excited,” Mungin tells KGW8. “I’m excited when projects like this come around because it’s an opportunity to show off what we are capable of doing.”
Mungin and Weislogel designed a series of eight demonstrations for NASA astronauts Christina Koch and Drew Morgan and European Space Agency astronaut Luca Parmitano to perform aboard the ISS National Laboratory.
"It's not often for your job on the space station that you're given a couple of hours to play with slime, with the ground teams directing you to shoot your friend with slime from a syringe or fill a balloon with slime," Koch tells Ashley Strickland of CNN. "My favorite thing about that experiment is that it highlighted the concept of curiosity leading to discovery. This is discovery-based science. It's why we seek knowledge."
If you’re wondering what we could hope to learn from sending slime into space, the answer lies in its very name. Slime is slimy, which adds up to its being a fluid that is thicker, or more resistant to flow, than fluids like water. To be precise, slime is around 20,000 times more resistant to flow than water, something physicists call a substance’s viscosity.
This makes slime behave in unexpected ways in the microgravity of the ISS, and improving our understanding of how more viscous fluids act in space may help improve the design of systems that were designed with Earth’s gravity in mind.
Without the gravity we’re used to, bubbles don’t rise, droplets won’t fall and equipment involving liquids, such as boilers, condensers, plant watering systems, blenders or coffee cups, become useless, Mungin and Weislogel explain in a release.
"Interestingly, we define liquid on Earth as something that takes the shape of its container," Koch tells CNN. "Water just turns into a sphere in microgravity, so we've had to remake definitions of different kinds of matter in space. This experiment is a great demonstration of how microgravity can contribute to our understanding of things on Earth, especially the things we take for granted."
The astronauts dutifully dispensed blobs of slime that formed floating green spheres. Water, by comparison, also formed floating blobs, but, because of water’s lower viscosity they kept wobbling in amorphous shapes long after the slime balls had stabilized into perfect orbs.
In another experiment, Parmitano got slimed when Koch fired a slime jet through a hovering green droplet. Koch expected a slimy explosion when popping slime-filled balloons, but when the balloon ruptured the slime scarcely moved, holding virtually the same shape.
An impromptu test yielded one of the more interesting results. Along with the packets of slime, the astronauts had been sent two paddles with water repellent, or hydrophobic, coatings. Parmitano squished a glob of slime between the paddles and pulled the paddles apart at different speeds.
Though the paddles were hydrophobic, the slime stuck to them and when Parmitano pulled the paddles apart slowly he briefly created a short slime bridge that then snapped, with the slime returning to the surface of each paddle. When he pulled the paddles apart quickly, a much longer slime bridge formed and then suddenly broke apart into a series of slime small balls spanning the distance between the paddles.
The experiment provided a perfect demonstration of why slime is what’s known as a non-Newtonian fluid. Such fluids are so-named because they break Newton’s law of viscosity, which states that a fluid’s viscosity shouldn’t change if force of one kind or another is applied to it, per Encyclopedia Britannica. The slime acted differently when Parmitano changed the force he applied to it by pulling faster, proving slime a textbook non-Newtonian fluid.
CNN reports that Mungin once saw this same phenomenon in Weislogel’s class, but that demonstration didn’t involve slime. Instead, it took place beneath a microscope. That’s because Newtonian fluids like water act like super-viscous non-Newtonian fluids, like slime, at small scales. This finding is one of the many ways these slime experiments can help researchers more effectively manipulate liquids in space.
Weislogel tells CNN the unique behavior of fluids in space could be used to create systems that move liquids like fuel or wastewater without pumps, or that automatically water plants without making a mess.
The experiments were decidedly messy, but Mungin tells KGW8 she hopes they help inspire kids to get involved in science, technology, engineering and math.
“Sometimes people have this very rigid idea of what science looks like, what a scientist looks like,” she tells KGW8. “And even though we're having fun—we’re having an incredible time—we're also getting immense amounts of data that we could never get otherwise."