Kimiya Yui helped set up the exposure experiment on the International Space Station in 2015.
JAXA / NASA
Space is not good for the human body, but microscopic organisms like fungi and bacteria seem fine when exposed to the void. Some mushrooms that have found a home on the International Space Station even find the conditions preferable –. This type of evidence has led some scientists to conclude that microscopic organisms could be ejected into space and potentially move between planets and sow life in the cosmos.
It's a controversial concept known as "panspermia", and it wasin the past as an alternative theory for the beginning of life.
In a new study published in the journal Frontiers in Microbiology, Japanese researchers sent densely packed spheres of bacteria to the International Space Station and taped them to the outside of the laboratory, where they were exposed to the hard, cold, and highly radiant vacuum of the room.
The experiment known as Tanpopo has been running since 2015. Tanpopo means dandelion in Japanese, and the experiment is so named because the dandelion spreads its seeds with the wind. Could the same thing happen to radiation-resistant bacteria in space? Akihiko Yamagishi, astrobiologist at the University of Pharmacy and Biosciences in Tokyo, wanted to answer this question back in 2007 when his experiments were first accepted as a candidate experiment on the ISS.
Yamagishi does not see himself as a proponent of panspermia, but wanted to know whether there are ways in which microbes can survive a journey from earth to another place in the cosmos.
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When the Japanese Space Agency's Handrail Attachment Mechanism experiment was installed on the ISS in 2015, Yamagishi and his team finally had the opportunity to conduct their research. By placing colonies of the radiation-resistant Deinococcus in wells and repeatedly drying the suspensions in the air, they were able to create "pellets" of bacteria. In 2015 these pellets were installed on the space station in panels on board the ExHAM.
Simultaneous experiments were designed to examine the pellets after one, two and three years. The experiment was officially completed in 2018 and the Yamagishi team has been analyzing the data ever since.
The most important finding shows that these pellets can withstand damage from UV radiation in space much better if the pellets were thicker. When the pellets were about half a millimeter thick, the outer layers of bacteria began to break down, but those in the middle survived. Yamagishi and his team argue that these thicker bacterial pellets exposed to interplanetary space could survive for two to eight years – theoretically long enough to be expelled from the earth and get to one of our closest neighbors.
"The results suggest that radiation-resistant Deinococcus could survive during the journey from Earth to Mars and vice versa, which is in its shortest orbit for several months or years," said Yamagishi.
Panspermia proponents suggest that some bacteria may be able to make interplanetary journeys trapped in meteorites and micrometeorites, a theory known as lithopanspermia. Yamagishi's work explored another theory – that these spherical colonies of bacteria could protect themselves. This is known as Massapans sperm.
However, there are a number of persistent problems. A direct shot from Earth to Mars isn't exactly the most likely route microbial adventurers could take.
"In theory, if you're hitchhiking, the time could be months or years"says Brendan Burns, an astrobiologist at the University of New South Wales who is not involved in the study." However, when it comes to "natural" travel, the likelihood of an object being ejected from Earth and hitting Mars in a short period of time is slim. ""
While Yamagishi's research shows the ability of bacteria to survive in space for extended periods of time, Burns says meteorites can have a flight time of more than 10 million years before jumping planets.
And there's a pretty big problem to overcome when you're microscopic and trying to move from planet to planet. First you need to be ejected from your home planet without dying, survive the long (really long) journey through space, and then endure an atmospheric re-entry. Even.
Yamagishi agrees. "Very little is known about ejection and injection," he says.
But let's say Deinococcus survived it all. What happens when the bacteria come into their new home? The situation is likely to be dire for an earth transplant accustomed to a world with running water and protected by a dense atmosphere.
"Even if a certain form of life could survive interplanetary travel, the conditions under which it ends must be just right for it to take off again," says Burns. He notes that the microbes need to search for nutrients and be robust enough to withstand differences in the atmosphere. While the panspermia hypothesis remains possible, Burns says, "The jury is still very undecided."
Yamagishi's team and the Tanpopo mission will continue exposure experiments "with different species under different conditions" in the hope to see how general the process of Massapans sperm can be.