Imagine that, for billions of years, you’re a grain of material unbothered on asteroid Ryugu. All of a sudden, a spacecraft flies down, shoots you with a pellet to kick you up, and collects you, taking you back to Earth. There, you are opened under the most pristine conditions – scientists are keen to study you in detail. And still, germs get to your surface. Life really does find a way, huh?!
This is not a fantasy tale – it is what happened to grains collected by Hayabusa-2. The Ryugu sample has been revolutionary: It was kept hermetically sealed from collection to its delivery to the labs of the Japanese Space Agency (JAXA). There, it was opened in pure nitrogen in a clean room, where all the tools were sterilized and kept under nitrogen.
That material is abiotic. It formed in space without any life whatsoever. But it contains lots of goodies, lots of munchies for terrestrial microbes.
Dr Matthew Genge
Parts of the sample were sent out to many labs, and once the team at Imperial College London started analyzing them, they saw something unexpected. Observations of the surface showed rods and filaments of organic matter. This was evidence of microorganisms – but it is most definitely not aliens. The data show that the contamination is very much of this Earth.
“It was a really big thing, looking at Ryugu for the first time and there was this mysterious stuff,” lead study author Dr Matthew Genge from the Department of Earth Science and Engineering, Imperial College London, told IFLScience. “You have to imagine I’m sitting there with a couple of undergraduate students, one of which is so excited she keeps falling off her chair. On the very first scanning electron microscope, session I noticed these little organic fibers.”
“We thought about it and realized they might be microbes, which of course was tremendously exciting, especially for the undergrads. But I knew from previous studies that terrestrial bacteria have been found in meteorite specimens. The second time we looked at the specimen, a week later, the number of these little fibers had increased by a factor of more than 10. There were just clusters of them around some of the indigenous organic material within the meteorite.”
Asteroid Ryugu was altered by water and contains organic molecules older than the Sun. The building blocks of RNA and Vitamin B3 have been found in its samples, together with polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, a molecule used in mothballs. Earthly bacteria don’t seem to care where the molecules originated from.
“Of course, that material is abiotic. It formed in space without any life whatsoever. But it contains lots of goodies, lots of munchies for terrestrial microbes,” Dr Genge explained to us. “Terrestrial microorganisms, especially bacteria can metabolize a very wide range of organic molecules.”
Despite the abundance of food, the scientific work conducted on the asteroid sample soon spelled the demise of these bacteria. Researchers needed to get to the molecules under and around them, which is a pretty intense process if you are a microbe.
“We were doing pretty horrible things to them because we were putting them in a scanning electron microscope, exposing them to hard vacuum shoot an electron beam at 20 kilovolts at them,” Dr Genge told IFLScience. “Most organisms don’t like that much, I wouldn’t have survived as long as those bacteria. So they were stressed, they were very stressed and that’s probably why they started to die.”
The findings raise an important point when it comes to contamination of samples. Even in the best conditions, a single spore can easily spread over extraterrestrial material. Finding evidence of life via meteorites even when they are collected shortly after their fall is likely to be impossible, unless that life is nothing at all like Earth. Even a sample collected elsewhere might face the same concerns.
“One day we’re going to make the discovery of life on another planet. We’re going to find microorganisms, probably in a rock that’s been brought back to Earth. When that day happens, one would like to think that we’re all going to be jumping up and down and celebrating. But in actual fact, somebody’s going to ask the question: ‘But are these from Earth?’ Because there is always a very, very slim chance. And that’s all you need. That’s all you need,” Dr Genge told IFLScience.
The paper is published in the journal Meteoritics & Planetary Science.
