Last year, a study reported the discovery of organic molecules on asteroid Ryugu, sparking discussions about the origins of life and the possibility of panspermia — the idea that life could be seeded across celestial bodies. However, a new study throws a wrench in those discussions, suggesting that the detected organic compounds were likely terrestrial contaminants, despite stringent precautions.

Microbes — the ultimate colonizer

The Hayabusa2 mission, launched by the Japan Aerospace Exploration Agency (JAXA), marked a historic achievement in space exploration. In 2020, it successfully returned samples from asteroid Ryugu, located over 100 million miles away. The samples were carefully handled in state-of-the-art clean rooms under nitrogen, with every precaution taken to prevent contamination.

Despite this, a study led by Dr. Matthew Genge from Imperial College London reveals that Earth’s microorganisms likely colonized the samples. The team observed microbial growth patterns consistent with Bacillus species, a type of bacteria capable of surviving extreme conditions.

A team of researchers led by Matthew Genge at Imperial College London confirmed that the asteroid has organic molecules; it confirmed that the samples actually have signs of life — but this life doesn’t come from 100 million miles away. It comes from Earth.

Researchers followed the microorganisms for around two months, observing a predictable pattern: after an initial growth phase, the population declined as it had no more resources. This growth pattern is exactly what you’d expect from microbe life cycles under nutrient and environmental stress, and the timing (a generation of around 5.2 days) is consistent with certain Bacillus species.

“The population statistics indicate an extant microbial community originating through terrestrial contamination,” the researchers explain in the study. “The discovery emphasizes that terrestrial biota can rapidly colonize extraterrestrial specimens even given contamination control precautions.”

What this means for the contamination of space samples

Bringing back samples from outer space without contaminating them is a massive challenge; researchers already knew that. Our planet is teeming with organisms that have occupied every possible niche and can live in pretty much every environment you can imagine. Ensuring that the shuttle equipment is sterile is only half of the challenge — the other half is making sure the samples don’t get contaminated upon reentry into Earth’s atmosphere.

This study highlights how even slight exposure can lead to microbial colonization of space-returned materials. This is important for all samples, and particularly for astrobiological studies, where distinguishing indigenous extraterrestrial life from Earth-based contamination is paramount. The findings suggests that microorganisms from Earth can metabolize extraterrestrial organic matter with no problems.

“Several procedures can be used to minimize the likelihood of colonization,” the research notes. “Preparation of thin sections in an area separate from terrestrial samples is recommended. Storage of samples in a dry inert atmosphere, such as nitrogen, provides a means of inhibiting microbial population growth simply through the minimization of adsorbed water. Direct observation of samples by scanning electron microscopy is also shown to be effective in identifying the presence of extant microbial communities, through analysis of their population statistics.”

However, there’s also a silver lining. The microbes only penetrated the first few microns of the sample, giving confidence that even if contamination exists, it can be removed. In addition, no other microorganisms were reported in any of the Ryugu samples. So, under the current protocols, the risk of contamination is still low (but not zero).

This sample brought an important lesson. From this, researchers can make improved protocols to handle and analyze the samples, bolstering the integrity of extraterrestrial sample analyses. As we look for signs of life beyond Earth, these findings remind us just how resilient life is here on our planet — and how ready it is to jump on every grain of soil.

Journal Reference: Matthew J. Genge et al, Rapid colonization of a space‐returned Ryugu sample by terrestrial microorganisms, Meteoritics & Planetary Science (2024). DOI: 10.1111/maps.14288