[annie123 (OP)]

If a body were buried in a vacuum could it remain fresh? or would the oxygen in the tissues and the bacteria in the body cause it to decompose?
And why do bodies buried in peat stay in shape - i thought peat was acidic?
And why do bones stay in one piece for so long?
And how cold does one have to get before freezing to death?
I'm not morbid - but i heard 4 podcasts called talking about death on the BBC and these questions weren't answered.

[Kryptid]

The exact conditions would be important. If you are talking about a human body floating in the vacuum of space, then the fate of that body will be strongly influenced by where it is. If it is far from sources of heat, such as the Sun, it will eventually cool off enough from water evaporating through the skin and mucous membranes and thermal radiation to freeze. That will preserve it for a while, but cosmic rays would cause cellular damage over longer periods of time. Close enough to the Sun, it could potentially remain warm enough for the anaerobic bacteria in the gut to start decomposing the body. Then again, cosmic radiation may well kill gut flora before they could do that. I'd probably need to see the numbers first.

[evan_au]

If a body were buried in a vacuum could it remain fresh?

If a body were exposed to a vacuum out near the orbit of Saturn, it would quickly freeze solid, and all life processes would stop, preserving the body.

However, freezing causes ice crystals to grow, puncturing cell membranes.
So the body would be "fresh", but if you tried to defrost the body, it would turn to mush.

And why do bodies buried in peat stay in shape - i thought peat was acidic?

Yes, acidic and low in oxygen. This slows down many kinds of bacteria.
If it is also very cold, that slows down most kinds of bacterial decomposition, preserving the soft organs.
But the acid will often break down the bones.
See: https://en.wikipedia.org/wiki/Bog_body

And why do bones stay in one piece for so long?

Outside a bog, or other forms of mummification, bacteria and fungi will quickly break down the skin and soft organs, as they contain readily-accessible water, fats and proteins. Insects, rats and vultures also make quick work of bodies.

However, bacteria are not so good at breaking down bone, especially the hard enamel of teeth.

If there are scavengers around (like hyenas), they will often disturb the bones, and crunch into them to reach the marrow.

In the ocean, bone worms make quick work of whale skeletons, despite the 4C temperatures in the deep ocean.
https://en.wikipedia.org/wiki/Osedax

And how cold does one have to get before freezing to death?

If your core temperature drops below about 35C, you are suffering from hypothermia.
With a core temperature below 20C, most bodily functions cease and you are effectively dead.
However, there have been cases where children have been resuscitated after falling into frozen lakes and rivers, with core temperatures as low than this. At low temperatures, oxygen consumption is reduced, delaying brain death from oxygen starvation (hypoxia).

How long it takes to drop your core temperature this low depends on many factors such as the external temperature, the duration of exposure and the thermal conductivity of the environment.
- A frozen ocean has a temperature slightly lower than 0C, but the thermal conductivity is very high. You can die in a couple of minutes.
- A child has a large surface area compared to their mass, and lose heat very rapidly
- Antarctic explorers have survived bitterly cold temperatures for long periods with very warm clothes, but are likely to suffer from frostbite and gangrene.
- Wind greatly increases heat loss from the body, the "wind chill" factor.
- Members of the 300 Club have survived temperatures of -100F outside at the South Pole in the middle of winter with no clothes - for a minute or so.

See: https://en.wikipedia.org/wiki/Hypothermia

[mrsmith2211]

Would there be evaporation in a complete vacuum?

[Kryptid]

Would there be evaporation in a complete vacuum?

Every substance has a finite vapor pressure. As long as the temperature is sufficiently above absolute zero, it should evaporate in a vacuum (potentially very, very slowly if it's too far from a source of radiation to make it a little warm, though).

[chiralSPO]

Since the OP says the body is "buried in a vacuum," I will take that to mean that the body is in an airtight container, which otherwise contains no matter, and is itself buried.

The next important question is how big is the container?

The smallest possible case, the inside of the container has exactly the same volume as the body (I immediately regret imagining a body in large vacuum-sealed plastic bag, and apologize for the image--you can also imagine a person encased in a block of lucite, if that is preferable). In this case there really isn't a "vacuum" there just isn't anything else there. If there are live anaerobic bacteria   inside the body (as there should be in any recently deceased human), they will probably eventually go rogue and do some biological digestion. But if we assume that everything is rendered inanimate, we would still definitely expect chemical degradation of the body. When we are alive, we expend vast amounts of energy (most of our metabolism) maintaining an artificial chemical equilibrium often called homeostasis (I would also consider polarized neurons as part of this). Once we die and stop expending energy to maintain the balance, everything is going to go to a new equilibrium state (which will probably take months or years to fully stop, at which point the body will probably just be a skeleton in a mixture of salty, gelatinous water and grease with some bubbles of low-solubility gases).

In cases where the volume of the casket (gasket?) increases then the volatile components of the body have the option of escaping into the gas phase (essentially just water at the beginning, but also other small molecules will be produced as decomposition occurs.) But I think the container would have to be pretty big for it to make much difference. If the casket is at 25 °C then water has a vapor pressure of 0.0313 atm, which means you would need a coffin at least 43000 times the volume of water in the body for all of the water to be in the vapor phase (I can provide calcs for that, if asked). So, yes, in space rapid mummification is totally possible, but not in a container, unless the person is sealed in an enormous underground cavity the size of a small pyramid (which could be pretty cool, I guess, but very expensive).