Asteroid samples returned to Earth had been instantly colonized by micro organism

We have known for some time that complex chemistry occurs in space. Organic molecules have been detected in cold molecular clouds, and we have even found sugars and amino acids, the so-called “building blocks of life,” in several asteroids. The basic materials for terrestrial life are common in the universe, and meteorites and comets may even have seeded the Earth with these basic materials. This idea is not controversial. But there is a more radical idea that the Earth was endowed not just with the building blocks of life, but with life itself. It's known as panspermia, and a recent study has brought the idea back into the popular science headlines. But the study is more subtle and interesting than some headlines suggest.

Panspermia became popular in the 18th and 20th centuries when it became clear that life on Earth arose surprisingly early. At a geological level, cellular life emerges almost as soon as the Earth cools enough to support it. Given the complexity of DNA and living cells, how could something like this evolve so quickly? In the panspermia model, life evolved either in space or on a distant planet and was carried to Earth by asteroids or comets. We know that some creatures can survive the harsh vacuum of space, so perhaps we have an extraterrestrial origin.

But there are reasons for skepticism. For one thing, the transition from organic to biological chemistry could be remarkably adaptable. Although life appears to have suddenly appeared on Earth, it could be exactly what you would expect. Without an example of extraterrestrial life, we simply don't know. And while life can survive in space for a limited time, it is unlikely to survive the millions of years it would take an asteroid to traverse the solar system, let alone the billions of years it would take to travel between star systems . Still, one step toward detecting panspermia would be to collect material from an asteroid and find out that there is life, and that's exactly what this latest study has found.

The Hayabusa2 mission, launched in 2014, landed on a small asteroid called Ryugu in 2018 and returned a sample of material to Earth in 2020. The sample was kept sterile throughout, hermetically sealed for the return journey, and only opened in a pure nitrogen clean room with sterilized equipment. The sample was as clean and uncontaminated as we could get. When the team prepared a sample and examined it under an electron microscope, they found rods and filaments of organic material consistent with microbial life. In other words, the team found life on an asteroid.

Except they probably didn't.

The size distribution corresponds to terrestrial life. Photo credit: Genge et al

Remember that microbial life is incredibly robust. It exists everywhere and spreads quickly. You can find the stuff in the cores of nuclear power plants, in hot thermal springs and in the cleanest clean rooms. And even if you sterilize something, microbial life finds a way. When the team discovered life in their sample, they first looked for evidence of contamination, and there was plenty of evidence. First of all, the size distribution of the organic rods and filaments found in the sample is consistent with those commonly deposited by terrestrial life. Their data also found evidence of a growth and decline period of about five days, which is also consistent with life on Earth. If the Ryugu samples actually evolved beyond Earth, they would be genetically separated from us by millions or billions of years. Their size and growth rate would not match those of our ordinary microbes. So the best explanation is that the sample became contaminated despite our best efforts.

Although the study doesn't support the panspermia model, it does tell us two important things. First, our sterilization procedures are probably inadequate. We may have already accidentally transferred life to the Moon and Mars. Second, asteroids are made of organic material that could sustain life on Earth. This is good news if we want to establish ourselves elsewhere in the solar system. Life on Earth may not have started in space, but it could very well end there.

Reference: Genge, Matthew J., et al. “Rapid colonization of a Ryugu sample returned from space by terrestrial microorganisms.” Meteoritics and Planetary Sciences (2024).

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