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You are on a ship in the cold vacuum of space. You find a body of an astronaut exposed to vacuum (for this instance just assume human, but you never know).

The body was essentially freeze dried and all microbes and moisture 'removed', as this question pointed out. The decay of a body in space has been answered in this question.

For this scenario, let us assume that it hasn't been exposed to the sun's radiation (or at least hasn't been exposed to multiple freezing/thawing cycles) and is still fairly intact.

This body is brought on board your spacecraft. What happens to it next?

Will the body start to decay once it is 'thawed' out, or will it remain 'perfectly' preserved. I'm curious if all the micro-organisms necessary for decomposition would remain completely dead; no hidden Tardigrade-type critters? Would contamination from live humans/animal test subjects provide a source for decomposition to start in the preserved body?

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    $\begingroup$ "I'm curious if all the micro-organisms necessary for decomposition would remain completely dead; no hidden Tardigrade-type critters?" Given the amount of sterilisation that probes ..machinery, intended for planetary exploration are put trough, I'd say the case for life surviving for long periods in a biological body is considered wide open at the moment.. They might figure 'better safe than sorry' when it comes to the machinery, but given that we are finding life in ever more extreme environments, I would almost expect some microbes to survive in a body exposed to space. $\endgroup$ – Andrew Thompson Aug 2 '16 at 19:01
  • $\begingroup$ Have there ever been any experiments on this subject, or is it all theory and speculation? $\endgroup$ – Organic Marble Aug 11 '16 at 20:04
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Just because there are answers to those questions, doesn't mean they are right. The quote from a magazine in this answer but it seems to be a dead link now: http://scienceinfocus.co.uk/qa/would-corpse-decay-space. But that quote does point out that it won't necessarily be completely dessicated like "freeze dried instant coffee".

It points out that there are competing processes. While water near the surface will be under osmotic-type pressure to diffuse to the surface where it can evaporate while it's still warm, the "big chill" will set in. Once ice, the mobility of the water molecules will be greatly, greatly reduced. It's not solid ice - there are pockets of ice in each cell and the cell walls will be busted up, but there is still a whole lot of cell walls to traverse, and only water molecules that are on surfaces and aren't inside ice will have mobility.

How cold will it be?

Let's try a little physics. Assume we're at 1.5 AU (Mars neighborhood). At earth, the total power is about 1.5 kw/$\text{m}^2$, at Mars $I_{sun}$ would be that times 1.5 $\text{}^{-2}$ or about 670 W. Let's say the cross-sectional area of a space suit intercepting sunlight $A$ is 1.0 m $\text{}^2$ and the total surface area for radiation is 2.5 m $\text{}^2$.

The power input from the sun will then be:

$$ P_{in} = I_{sun} A \alpha$$,

where $\alpha$ is the absorptivity of the white space suit in the visible and near-infrared wavelengths. I'm going to ballpark the diffuse reflectivity at 0.8, and call the absorptivity 1-0.8 = 0.2

Putting in numbers, I get 134 W. Since it's probably going to be spinning, I'll make a simplification and treat this as an equilibrated object. The whole surface area will be at a uniform temperature, and that temperature will be the value that allows it to re-radiate those 134 Watts.

The Stefan-Boltzmann Law says:

$$ P_{out} = A \epsilon \sigma T^4 $$,

where $\sigma$ is the Stephan-Boltzmann constant and is about 5.67E-08 W m${}^{-2}$ ºK ${}^{-4}$, and $\epsilon$ is the dimensionless emissivity (between 0 and 1).

Now you might think that a white space suit with a 0.2 absorptivity should also have an emissivity of 0.2, but these things are not constants. They can depend strongly on wavelength. Most things that look white still have an emissivity at longer wavelength infrared (where "cool stuff" radiates) above 0.9. If you go to the linked Wikipedia article for emissivity again, it says:

Paint (including white)   0.9
Paper, roofing or white   0.88 to 0.86
Snow                      0.8 to 0.9
Water, pure               0.96
Concrete, rough           0.91
Glass, smooth (uncoated)  0.95

So if you had infrared eyes (say 15 or 20 micron wavelength) all those things would be pretty much black. None of them would be transparent. Snow is black sand. Water is ink, "transparent glass" is obsidian or black marble, and white paint is black paint. Actually all paint is black paint.

Clean bare metal is brilliant, but let it oxidize and it will darken as well.

If you think about it, those infrared thermometers - while they do or should have an emissivity setting for accuracy - tend to work without it, because "most stuff" is roughly 0.9 at room temperature, and they often have a default of 0.90 or 0.92 or something like that in the firmware, if you don't specify one.

Nice unoxidized metal surfaces however are good reflectors at visible wavelengths, through infrared all the way down to radio. Those can be down around 0.1 and below.

So let's just chose 0.9

$$ P_{out} = P_{in} $$

$$ A \epsilon \sigma T^4 = P_{in} $$,

$$ T^4 = \frac{P_{in}}{A \epsilon \sigma} $$,

Plugging the numbers in I get 180 K. That's c-c-c-cold, about -93C.

Solid ice on the moon, exposed to space (but not sunlight) for millions of years is expected to be stable at 100K (see Lunar water). While we're not that cold, this is not exposed - it's deeply embedded in a complex biological and crystalline ice matrix, and we may be talking about years or tens of years - faster if David Bowman is in his pod.

The body will probably have a substantial amount of ice. If you bring it in to room temperature it will have some water in it. It will maintain integrity to some degree, which means any bacterial spores (some bacteria have spores) and fungal spores (in other places) may activate, even if only one in every billion bacteria actually survives being frozen in ice, it's going to be a LOT of them. New surface contamination will be present too. It's a race against time between all those competing biological sources.

Not, it won't be a dried out mummy. It will become a problem inside a spacecraft. Keep it frozen, or outside, but I personally prefer to leave it (or me) as a burial at sea so to speak.

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    $\begingroup$ Maybe you'd want to have a way of deorbiting bodies, so that they burn up in the atmosphere instead of becoming navigational hazards. $\endgroup$ – Howard Miller Aug 12 '16 at 1:17
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    $\begingroup$ @HowardMiller OK but if you start down that road you'd be obligated to pick up all the space junk - and put it inside your spacecraft? Can you come up with a scenario where removing this one item from space would be mission critical? These days things are tossed (or deployed) from the ISS all the time because orbital mechanics (and tracking) seems to work. I'm imaging a deeper space scenario where "space is big - really big" applies. LEO objects at the very low ISS altitude will reliably de-orbit. $\endgroup$ – uhoh Aug 12 '16 at 2:20
  • $\begingroup$ @HowardMiller This has got me thinking (oh no!) I've asked this question, let's see if it flies. You can also consider SuitSat! Also here at NASA. $\endgroup$ – uhoh Aug 12 '16 at 2:37
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This has happened once, kind of. Soyuz 11, which was re-entering Earth, had a loose valve that subjected it to the vacuum of space. The astronauts returned to Earth eventually, with the capsule in perfect condition. A few things of note:

The autopsies took place at Burdenko Military Hospital and found that the cause of death proper for the cosmonauts was hemorrhaging of the blood vessels in the brain, with lesser amounts of bleeding under their skin, in the inner ear, and in the nasal cavity, all of which occurred as exposure to a vacuum environment caused the oxygen and nitrogen in their bloodstreams to bubble and rupture vessels. Their blood was also found to contain heavy concentrations of lactic acid, a sign of extreme physiologic stress. Although they could have remained conscious for almost a minute after decompression began, less than 20 seconds would have passed before the effects of oxygen starvation made it impossible for them to function.

Also of note is this video, showing support crews attempting CPR on the cosmonauts. If you want to see that, check it out at YouTube

Would they decompose after being brought back in to a human environment? Yes, eventually. It would probably be somewhat slower than otherwise.

There is some evidence that the decay process would be different. Of some note is the forest around Chernobyl. Of some note, they did an experiment where they took leaves that hadn't decomposed for an extended period of time in a high radiation area, and brought them to a low radiation area. The leaves decomposed as expected. So one can expect that the decomposition process would return to normal, given the correct enviroment.

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    $\begingroup$ @uhoh Good thought I suppose. It's surprisingly difficult to not auto-embed YouTube videos, but I think I've managed it. $\endgroup$ – PearsonArtPhoto Aug 13 '16 at 11:48

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