Well its about 10 K in space. That 10 deg above absolute zero... so the body would be frozen. Also there is not atmosphere so that would help preserve as well... so eventually the body would evaporate but for a long time it would just be frozen solid...

The major cause of decomposition is the body's own bacteria, so it is possible for an astronaut to decompose. The two factors that could potentially preserve the body are drying out or freezing. Either would prevent the bacteria that cause decomposition from functioning.Despite the commonly held conception about bodies freezing in space,drying out is probably more likely.Heat transfer happens very slowly in a vacuum. Usually the majority of heat transfer occurs by conduction or convection which are not possible in a vacuum. Heat can only very slowly radiate away from the body. In fact, spacesuits are generally used to cool off astronauts, not to keep them warm. If the skin is uncovered, most of the heat will actually be removed from the body by the evaporation of water which will also occur slowly. At low pressures, water evaporates more readily at lower temperatures and carries heat away from the body (think about what it feels like to have water evaporate off of your skin).

I do not know enough to say for certain under what conditions the body will decompose, but it will depend of two things: how fast water is lost from the body and how fast the body cools off. Both of these factors will depend on whether or not the astronaut was wearing a spacesuit. The spacesuit would help to keep water in the body from evaporating/boiling away and also to keep the body from cooling off.

Let's look at 3 cases:
1) The astronaut is lost and dies because his suit runs out of oxygen(but remains sealed)
2) The astronaut's suit gets a hole in it and all of the oxygen leaks out
3) The astronaut has no suit

1) In this case, as long as the spacesuit's temperature regulation continues to function, the astronaut would remain at about body temperature and even after it ceased to function, the suit and space itself would continue to act as an insulator. It would be a long time before the body could cool off. There would be plenty of time for the body's own bacteria to decompose the body. In fact, the environmentwould be fairly similar to a body buried in a sealed coffin and Iwould guess that the decomposition should be fairly similar to thatsituation.

2) In this case, the exposure to vacuum would cause all of the oxygen(including oxygen dissolved in blood) to leave the body. However, the bacteria that cause decomposition are anaerobic so this would not prevent decomposition from occurring. Since space is essentially a vacuum and vacuums are insulating and have poor heat transfer, the body would not cool quickly, especially since it would mostly be protected by the spacesuit. The majority of the cooling that would occur would be due to water from the body evaporating. However, if there is only a small hole in the suit, water vapor will only escape from the body slowly. I am not sure how quickly the body would cool and dry out, but my guess is that it would have time to show noticeable decomposition before the body was too dry or cold to decompose further (It take about 2 days before the body will start to decompose noticeably).

3) This is the case I am not so sure about. The body will start to decompose, but I it may not decompose noticeably before enough water evaporates to halt the decomposition. There may not be enough scientific data to confirm what would happen in this case. However, I would guess that this situation is probably similar to what would happen to a body buried in a desert. A vacuum is probably at least as efficient at drying out flesh as dry sand which can preserve a body through natural mummification.

Interesting question. I suppose it depends on what you mean by decomposition. Most of what we mean is bacteria breaking things down. When living things die, their immune systems and other protective mechanisms shut down. That leaves bacteria free to consume the body, releasing nasty smells, liquefying tissue, and finally destroying almost everything except hair and bones. In a warm, moist environment, this can happen pretty fast.

Space is really cold and dry. That tends to minimize any bacterial growth. I would guess that it would stop it completely. Scientists have dug up bodies (at least one human and one mammoth that I can think of) that were frozen for thousands of years. They werent really decomposed the way we usually think about decomposition. Space would be even colder and drier than a glacier.

So if we were able to recover her or his body, it would be frozen, maybe dehydrated, depending on whether they were sealed in a spacesuit, but pretty well preserved. There would probably be lots of nice evidence for determining cause of death.

That would depend on whether the integrity of the astronaut's suit was compromised or not. If the suit were not compromised, then a form of decomposition would occur, but it would not be the normal decomposition that would happen on Earth because there would be no oxygen (presumably why the astronaut died in the first place). This means that the entire decomposition process would be undertaken by bacteria, and a different list of bacterial decomposers than under oxygenated conditions; sulfur would wind up being used instead of oxygen, and would lead to a lot of hydrogen sulfide being produced. There actually have been experiments done showing this, because animals buried in anoxic sediment represent a common way of obtaining outstanding preservation in the fossil record (e.g. the Burgess Shale), and these experiments were designed to try and elucidate how such preservation occurs and what it can tell us about the conditions of death and burial of the animals fossilized within.

However, if the suit were breached, all of the water in the astronaut's body would evaporate, which would lead to mummification, as happens to people or other animals that die in the midst of very harsh deserts on Earth such as the dry valleys of Antarctica. In this case, decomposition would not occur, as the decomposers would themselves be desiccated as well.