Would food (or people) decompose in space?

Question posed by @krunchie_frog, and many thanks to @squiggle7 for being my resident biomedical scientist.

When food decomposes, bacteria attack it and break it down into simpler substances. Most types of bacteria require three things to function: food, water and oxygen. Some types of bacteria do not need oxygen (these are called anaerobic bacteria) but still require the other two ingredients. So if we were to, say, throw a sandwich out of an airlock, would it decompose? Lets look at all of the necessary ingredients for decomposition in turn:

There are about 5 nonillion* bacteria on Earth and they are transferred to our food through the air or by touch. If you throw a sandwich out into space it's unlikely to pick up any new passengers, but it's highly likely that there will already be a significant number of bacteria already starting to munch their way through your lunch. Space food is irradiated in order to kill off as much of the bacteria as possible and therefore increase the lifetime of the food, but bacteria are hardy little things and it's nearly impossible to get rid of them all. However, there's a lot of radiation in space, so any food you throw out of an airlock will eventually have all of its bacteria killed off. This probably won't happen straight away, though.

Just as that sandwich is food for you, it's also food for the bacteria so there are no problems with this one.

There's no water in space, so if the bacteria are going to be able to break down your space-sandwich they'll need to get it from the food itself. The good news (for them) is that most food items have a certain amount of water in them. Space food, along with being irradiated (see above) is also often freeze-dried for the purposes of depriving bacteria of one of their raw materials.

There's no oxygen in space, at least not enough passing oxygen to be of any use to our bacteria. That means that this also would need to be supplied by the food that they're trying to decompose. Again, though, there's a fair chance that there will be some oxygen hanging around in air pockets in whatever's to be broken down- there are plenty of such pockets in bread, for example.

It looks, then, like a sandwich in space would have a fair chance of at least starting to decompose- food, water, oxygen and the bacteria themselves are likely to be present in small quantities, so decomposition could theoretically start and then continue until one of these ingredients runs out. But wait- there's one other thing we haven't yet considered:

Space is cold, and bacteria require a certain amount of heat in order to work properly (from memory, I think most bacteria prefer temperatures of around 40 degrees centigrade, but there are 'extremophiles' that can work, and indeed thrive, at much higher and much lower temperatures). Again, though, there will be a certain amount of heat stored in your ejected sandwich which means that our little friends have had yet another stay of execution.

The discussions above hinge around the idea of a sandwich being thrown out of an airlock, but can be applied to any organic matter finding itself in space. Linking the idea to Blogstronomy's previous post about the fate of a person finding themself in space without a suit we could say the following:

  • A human body is larger than a sandwich so will retain its heat for longer. It would also start off at a higher temperature, so the bacteria contained within would have a longer window of time within which to get munching.
  • The human body can be about 70% water at any one time and is larger than a sandwich so is likely to contain much more water, again allowing the bacteria to be active for longer.
  • The effects of vacuum exposure to a human body may cause dissolved oxygen to form gaseous bubbles in the blood stream, and oxygen will be available in other areas of the body such as the lungs and digestive tract.
  • A larger body would provide greater protection against radiation, increasing the survival time of bacteria.
In short...

It is unlikely that any food item or human body ejected into space would fully decompose. It would instead decompose partially (how much depending on the various factors discussed above- it may not even be noticable) and then become freeze-dried. It would then probably break up over time via the effects of collisions or radiation damage.

It crosses my mind, though, that a large enough organic body with the right balance of bacteria, oxygen and water could feasibly develop its own self-sustaining ecosystem, at least for a time...

* That's 5 million trillion trillion, or 5,000,000,000,000,000,000,000,000,000,000 of the little blighters.


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