We’ve known for a while that complex chemistry occurs in space. Organic molecules have been detected in cold molecular cloudsand we have even found sugars and amino acids, the so-called “building blocks of life”, within several asteroids.

The raw ingredients of terrestrial life are common in the universe, and meteorites and comets may even have seeded the Earth with these ingredients. This idea is not controversial. But there is a more radical idea that the earth was seeded not only with the building blocks of life but 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 19th and 20th centuries when it became clear that life arose surprisingly early on Earth. On a geological scale, cellular life appears almost as soon as the Earth cools enough to support it.

Given the complexity of DNA and living cells, how could such a thing have evolved so quickly? In the panspermia model, life evolved either in space or on some distant world and was brought to Earth within asteroids or comets. We know that some living things can survive the harsh vacuum of space, so perhaps we have some alien, extraterrestrial origin.

But there are reasons to be skeptical. First, the transition from organic to biological chemistry can be remarkably adaptive. Although life appears to have appeared suddenly on Earth, it may 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 cross the solar system, let alone the billions of years it would take to travel between star systems.

Still, one step toward proving panspermia would be to collect material from an asteroid and find out that it has life, and that’s exactly what this latest study found.

The Hayabusa2 mission, launched in 2014, landed on a small asteroid named Ryugu in 2018 and returned a sample of material to Earth in 2020. The sample was kept sterile throughout, hermetically sealed for the return trip, and opened only in a pure nitrogen cleanroom using sterilized equipment.

The sample was as pure and unadulterated as we could get. When the team prepared a sample and looked at 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.

One thing to keep in mind is that microbial life is incredibly robust. It is everywhere and spreads quickly. You can find the stuff in the cores of nuclear power plants, in hot thermal vents, and in the cleanest clean room. And even if you sterilize something, microbial life will find a way.

When the team found life on his testthe first thing they did was look for evidence of contamination, and there was plenty of evidence to be found. To begin with, the size distribution of the organic rods and filaments present in the sample is consistent with those commonly deposited by terrestrial organisms.

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 specimens had indeed evolved beyond Earth, they would be genetically separated from us for millions or billions of years. Their size and growth rate would not match those of our normal microbes. So the best explanation is that the sample got contaminated despite our best efforts.

Although the study does not support the panspermia model, it does tell us two important things. The first is that our sterilization procedures are likely inadequate. We may have already spread life to the moon and March unintentionally.

The second is that asteroids have organic material that can sustain life on Earth. That’s good news if we want to establish ourselves elsewhere in the solar system. Earth life may not have started in space, but it may well end up there.

This article was originally published by The universe today. Read it original article.