Did Microorganisms Come from Space?
Thinking about the Cosmic Scale of Cycles

How did life on Earth originate, and how has it continued to the present day? Interestingly, the core debate surrounding the origins of life has not yet been fully resolved scientifically. Did life arise spontaneously on Earth? Or was some “seed” of life brought from outside the Earth? Recently, a field of study called “astrobiology” has been gaining attention. By closely examining the composition of other planets, their moons, and asteroids in outer space, scientists are seeking to uncover the origins of life. This connection between “space exploration” and “biology” aims to pioneer new frontiers of knowledge.

Have you heard of Japan’s asteroid exploration missions, Hayabusa and Hayabusa2? The asteroid sand samples these probes brought back to Earth might lead to groundbreaking discoveries that could help unravel the mysteries of the origin of life on our planet. One of the primary goals of space missions led by NASA and the European Space Agency (ESA) is also to uncover the origins of life.

In the last two issues of Monthly JP pavilion, we discussed microorganisms on Earth. This time, we’re shifting our focus to space. Our theme is space and microorganisms. We interviewed Dr. Akihiko Yamagishi, who belongs to the society of astrobiology—dedicated to the comprehensive study of the universe and life—to explore this fascinating topic.

How Do Microorganisms Survive in Extreme Environments?

Dr. Akihiko Yamagishi, a scientist at Tokyo University of Pharmacy and Life Sciences, specializes in extremophiles—organisms that live in extreme environments—and conducts research on space and life. We asked him the pressing question that came to mind when we read the news mentioned earlier: How can microorganisms survive in space?

“The mechanism is simple. Microorganisms can’t survive in space on their own, but by clustering together, they can protect their inner parts by sacrificing their outer layers. It’s often said that organisms die in space due to intense radiation, but that’s not entirely true. The real threat is ultraviolet (UV) radiation. So, the outer layer absorbs the UV rays. Alternatively, if they are hidden inside a hard material like a stone, the microorganisms inside can survive for about a year.”

Microorganisms and the Possibilities for the Origin of Life

If organisms can survive in outer space, it seems plausible to consider that life on Earth may have originated from space. This idea, which assumes that the “seeds of life (spermia)”  are “universally (pan)”  present, is known as the  “panspermia theory.”  

On the other hand, there is also a theory that life originated on Earth. One prominent hypothesis is the “hydrothermal vent theory,” which suggests that life’s essential materials were generated through chemical synthesis near deep-sea hydrothermal vents where high-temperature water is emitted.

Did life emerge from Earth's oceans? Or was it brought from outer space? It is a truly fascinating debate. Dr. Akihiko Yamagishi, however, is skeptical of both theories.

“First, about panspermia. In my view, it simply suggests that life could have originated elsewhere and then traveled through space. But what I really want to know is how life came into existence in the first place. So, panspermia doesn’t truly address the origin of life. As for the hydrothermal vent hypothesis, life always contains nucleic acids, and the process of forming ribose, a key component, requires drying or the presence of land. Given this, it’s hard to argue that life originated in the sea.”

The story behind the origin of life varies among researchers, with experts from various fields proposing different theories from different angles. We also asked Dr. Yamagishi about his stance.

“I would have to say that we don’t know yet. Considering the conditions necessary for life, such as amino acids, energy, and dryness, I think the most likely location might be around hot springs in volcanic regions. But I don't want to make any assumptions just yet. I once made a premature conclusion in another study and realized how dangerous it is to be obsessed with ‘knowing.’”

Exploring Life’s Diversity

Even in this age of technological advancement, life and the universe remain enigmatic, making it a field filled with romance. Yet, it’s human nature to seek definitive answers swiftly. The allure of proposing hypotheses can be captivating, drawing many, but it also risks closing minds to other possibilities.

Dr. Yamagishi finds it intriguing to consider a scenario where microorganisms did not travel through space.

“I find it fascinating if microorganisms didn’t travel through space because it would imply independent life on each planet, fostering greater diversity. That’s what I meant by ‘intriguing.’ If it’s proven that various life forms evolved independently, studying their commonalities—such as the presence of 20 amino acids or nucleic acids—can elucidate the universal conditions for life. By comparing these conditions with their environments, we can determine the limits of where life can exist.”

The more samples of life we study, the better we can understand its origins. However, the possibility of microorganisms traveling through space suggests that the origins of life and the diversity of our samples may be more interconnected than we realize, potentially reducing our study to just one sample. This might seem like we’re straying from finding definitive answers, but science is about systematically eliminating possibilities.

Let’s dive into Dr. Yamagishi’s background. What sparked his interest in the origins of life?

“I've always been fascinated by the origins of the universe and life itself. That’s the only reason. Even as a child, I was captivated by Earth’s history and the evolution of life. In the science books I read back then, the entire history of the Earth was condensed into just one page, which, looking back, shows how little we knew then. But that was all we had. My interest grew more focused after returning to Japan following a postdoctoral fellowship in the U.S., when a friend shared an evolutionary phylogenetic tree published in Science or Nature. It amazed me how much we had learned about life. Looking back, I now realize the evidence seemed too tenuous to be fully credible (laughs).”

It was just before the 1980s when biology was exploring genetics. Despite Dr. Yamagishi’s interest in studying life’s evolution since the 1970s, the prevailing belief then was that life couldn’t be scientifically tested or verified. According to him, while the term “theory of evolution” existed, it was often perceived more as a concept of humanities rather than a strictly scientific one.

Launch of the Tanpopo Mission in 2007
Collecting Microorganisms in Space

It has been 50 years since then, and the world has changed dramatically. Numerous papers have been published on the origin of life, with each new hypothesis sparking intense discussions. In 2007, Dr. Yamagishi launched the Tanpopo mission to investigate the potential migration of microorganisms between planets.

“In 1986, the Soviet Union (now Russia) launched the Mir space station, and we received reports of mold growth onboard. Initially, I attributed it to human presence, but it sparked my curiosity about the possibility of microorganisms existing outside spacecraft. I was contemplating how to use airplane filters to collect and study sky dust when I saw that the Japan Aerospace Exploration Agency (JAXA) was accepting applications for airborne research projects. I applied, and our proposal was accepted, marking the beginning of the Tanpopo mission. We successfully collected Deinococcus radiodurans, a well-known bacterium among microbiologists.”

This led to further exploration. Recognizing the potential presence of more microorganisms higher in the atmosphere, the team opted to use a balloon to reach the stratosphere (10 to 50 kilometers above ground), higher than conventional aircraft could achieve. This second endeavor also yielded bacterial samples, expanding the mission’s possibilities.

While the process sounds straightforward, the actual work is exceptionally challenging. The stratosphere’s low atmospheric pressure, often one-tenth or one-hundredth that of ground level, and temperatures dropping below minus tens of degrees Celsius make human access impossible. Even automated microbial collection systems must withstand near-vacuum conditions outside. Additionally, the lid must close when the sample is dropped from the sky and lands on water, all of which must be done remotely. This requires robust communication technology, antennas, and other equipment designed for extreme environments.

Considering these challenges, one might wonder about the difficulties of collecting samples in space.

“In space research, we utilize aerogel, the lightest material on Earth. Composed almost entirely of air, it resembles solidified smoke. As microorganisms enter from space, they impact Earth’s atmosphere at speeds exceeding 8 kilometers per second—over ten times faster than a bullet due to Earth’s high rotational speed. The spacecraft, flying belly-down like an airplane, uses aerogel on its backside to selectively capture incoming particles from above. Slower microorganisms from the spacecraft adhere to the aerogel’s surface upon impact, while faster ones make holes through it, allowing us to examine them methodically. Currently, our aerogel onboard already contains approximately 300 impact sites. While most are likely remnants of micrometeorites, some may harbor microorganisms.”

Dr. Yamagishi previously expressed that it would be intriguing if microorganisms did not travel through space. However, a scientist’s duty involves impartially verifying facts based on data, regardless of personal interests. The findings from the Tanpopo mission could unveil new mysteries, shaping the research agendas of future scientists.

The Big Question
Can Life Exist Outside Earth?

So far, we have explored the possibility that microorganisms may travel through space. This raises an intriguing question: could life on Earth have originated on Mars? The idea of extraterrestrial life has fascinated us for decades, often depicted in movies and other fictional worlds.

“I think scholars have different hypotheses about this. For example, consider the biologist’s perspective. A biologist studying the SARC gene (a cancer gene that can cause cells to become cancerous) dedicates their career to it. If the SARC gene goes slightly wrong, humans get cancer. Given this, it is miraculous that humans can live for decades and that hundreds of millions of us do. Such a miracle might not be possible on any other planet, suggesting that aliens might not exist. On the other hand, physicists and astronomers might argue, ‘Why are humans special when other planets could have similar environments to Earth?’ They would think humans are just another species. From this view, it would be strange if there were no life on other planets, and there might even be more advanced civilizations elsewhere. So, depending on one’s research field and perspective, the possibility of extraterrestrial life could range from zero to infinite.”

In other words, we still don’t have a clear answer. Dr. Yamagishi, who continues his research across multiple fields in astrobiology, says, “We can’t see the finish line.” However, his expression and tone do not convey any sense of defeat. We are certainly learning more. The asteroid samples recovered by Japan's space probes "Hayabusa" and "Hayabusa2" may contain clues related to the origins of life. Research is advancing rapidly, constantly updating our understanding. Still, it is too early to draw any definitive conclusions.

Finally, let us return to the theme of “JUNKAN,” or cycles, promoted by the Japan Pavilion. Microorganisms drifting through space to reach Earth, and those leaving Earth might create unknown life forms on other planets. This represents the grandest story of cycles.

But from Dr. Yamagishi’s perspective, the word “cycle” also carries a warning.

“A cycle refers to homeostasis, meaning it does not change. This isn’t something humans created; it’s a natural process Earth has maintained for a long time. Earth contains many elements that return to their original states through feedback, helping to keep its temperature constant and maintain its natural environment. In other words, cycles have always existed. However, as Earth’s balance is now being disrupted, maintaining our current economic activities and lifestyles isn’t a ‘cycle,’ but rather ‘inertia.’ To protect Earth’s cycle, we must break out of this loop of inertia and try something new.”