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Humans are increasingly pushing into space: NASA’s Artemis program plans to return astronauts to the moon and establish a permanent orbiting lab in the next few years, and private companies like Blue Origin and Space X plan to ferry tourists beyond Earth for a price.
And where humanity goes, so goes human conflict. “We are by nature, unfortunately, kind of a violent species,” says Zackery Kowalske, a Ph.D. researcher with Staffordshire University in the United Kingdom, who is completing his doctoral research on the environmental influence on bloodstain pattern analysis while also working as a full-time crime scene investigator in the state of Georgia. “So as we become more of a spacefaring species, there will be space detectives who investigate crimes.”
Kowalske studies how blood splatters differently on concrete, snow, and sand. But he’s also a self-professed “huge space nerd,” so he began wondering how gravity—or a lack thereof—might influence blood splatter. “Gravity is always holding us down,” says Kowalske. “I started to have this idea about how blood would splatter in the absence of gravity.”
He ran a literature review of any space-related blood work and eventually got in touch with George Pantalos, a cardiovascular physiologist at the University of Louisville in Kentucky who studies surgery in space—including blood in space.
Kowalske and Pantalos met in person, over coffee, off an interstate, when Pantalos was driving to Florida for a zero-gravity flight campaign on a plane that flies parabolas to mimic the gravity of space flight. “Zack proposed a crazy experiment,” Pantalos recalls. “But I like crazy experiments because sometimes it’s fun. The craziest ones are the ones that you actually learn the most from and you learn to think differently. So I was intrigued.”
Pantalos has flown 62 zero-gravity flights. Kowalske wanted him to do an experiment on one of them: record in high-definition the splatter of blood from a syringe onto a paper target, which he could compare with the same experiment in normal gravity in his lab.
Pantalos knew there was often extra time built into these flights—extra parabolas flown, in case a given experiment failed. He told Kowalske that the next potential flight—aboard a modified Boeing 727 parabolic aircraft nicknamed the “Vomit Comet”—was in six months, in May of 2022. He promised to take the materials for the experiment with him, including synthetic blood made of 40 percent glycerin and 60 percent red food coloring (as real blood would contaminate the plane) and do his best.
There will be space detectives who investigate crimes.
It turned out they got lucky and there was indeed extra time on the next flight, so Pantalos was able to carry out the experiment. With the cameras running, he squirted the synthetic blood into the air 20 centimeters from the paper targets and captured the splatter inside a repurposed pediatric incubation chamber, called a glove box.
The results of that experiment appear in a new paper, out this month in the journal Forensic Science International: Reports. In it, Kowalske and Pantalos, together with colleagues from Staffordshire University and University of Hull, report that liquids with the viscosity of blood behave differently in space conditions. Like their blood substitute, blood is more likely to stick to surfaces in space than on Earth and should travel in a straight line rather than a parabola.
They also found that the force of surface tension of blood-like liquids is much greater in zero gravity, which surprised Kowalske. Surface tension is the cohesion of molecules in a liquid surface that allows it to resist external force—it’s why a steel paper clip, for instance, can rest on the surface of a glass of water. Surface tension, the researchers found, is the driving factor in deciding how liquids splatter on surfaces in space, both in terms of the shape and size of the pattern.
Just doing the experiment in zero-gravity was a new experience, Pantalos says. “Watching the splatter patterns as they happen was absolutely fascinating, because of the slightly different behavior without gravity being present,” he says. “The other thing ironically for me is I go to great pains to keep everything inside the glovebox tidy. I was giving myself the first opportunity to intentionally make a mess.”
Blood splatter forensics is a complex science. It isn’t as straightforward as it may seem on TV: It relies on considerable subjective interpretation by a forensic analyst. Today, many of the surfaces on Earth where experts may find blood splatter are made of highly engineered materials, such as scratch-resistant cell phone screens, anti-glare windshields, or hydrophobic surfaces. The newest blood splatter science is trying to determine how these new materials impact splatter patterns—which is similar to the kind of work Kowalske is doing in his doctoral studies.
Blood splatter patterning is the only type of forensics currently being tested in space, Kowalske says. It could be used in future analyses of accidents or catastrophic events aboard the International Space Station.
For the space medicine community, of which Pantalos is a part, the main objective is keeping people healthy in space. But at conferences and in reports, the community of space medicine experts also discusses what will happen when people die in space. And that could lead back to bloody questions at the new frontiers of astroforensics. 
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