What would happen to an astronaut if they floated off in space?
December 29, 2013 1:00 AM   Subscribe

After watching Gravity and Europa Report I started to wonder what would happen to an astronaut's body if they floated off in space. Googling reveals information about how long they'd be able to breathe (~8 hours) and that we have little jet packs that can help people maneuver, but nothing about what would happen over thousands or millions of years, assuming there's no way to rescue the astronaut alive or dead and they drift off into outer space, say on an interplanetary mission and not near the Earth's atmosphere to be burned up.

I want to know stuff like:

- Would the body decompose inside the space suit, or is everything sterile in there? Would bacteria inside the body decompose it inside the suit?
- Would the body freeze solid, or cook?
- Would space debris floating around or radiation eventually disintegrate the suit over time?
- Would the sun turn the suit completely white like the flags on the moon?

Basically, I want to know what we'd see if we stumbled across an astronaut who'd been long dead, floating around in space for a few thousand years.
posted by UltraFleece to Science & Nature (10 answers total) 9 users marked this as a favorite
It would probably help if you defined where the body starts from and it's trajectory over the thousands of years. Because a body floating in an orbit similar to mercury would experience different conditions than one on trajectory taking it out the solar system.
posted by Brandon Blatcher at 1:51 AM on December 29, 2013

Assuming being lost in deep space and not in the vicinity of a large gravitational mass, wouldnt the body would eventually become a frozen, endlessly floating astronaut-cicle? Space is pretty chilly. As long as the suit was not ruptured in any way (said astronaut died of a heart attack or suffocated) there may well be some decomposition after death but once the suits heating elements ran out of power, everything would freeze. Given the absence of any source of radiation other than background cosmic radiation, I would expect that the suit and the astronaut-cicle would be more or less perpetually intact.
posted by elendil71 at 2:51 AM on December 29, 2013

Space is vacuum and vacuum has no temperature. What most people refer to as the "temperature of space", 2.7° Kelvin, refers to the ambient infrared radiation of the universe left over from the big bang. An object left in interstellar space which is warmer than that will radiate infrared and get cooler. When it reaches 2.7° Kelvin, then the incoming infrared will balance the outgoing infrared, and the object will be at ambient.

2.7° Kelvin (about -270° C) is really, really cold. Everything except Helium is frozen at that temperature, and biological processes are completely shut down. There may be extremophiles which could survive that temperature and revive if they're warmed back up again, but they won't be doing anything as long as they're at that temperature.
posted by Chocolate Pickle at 5:09 AM on December 29, 2013 [3 favorites]

I read recently that space suits actually leak constantly at the glove and helmet attachments. Assuming that's correct, the suit interior would presumably be well below a life-compatible pressure well before any significant decomposition set in. My bet for a 10,000 year old dead astronaut is they're not decomposed, but they and their space suit have at least a few significant sized holes and are spinning very rapidly (both of these due to impacts from small particles traveling at a high relative velocity).
posted by russm at 5:18 AM on December 29, 2013

Vacuum, in addition to not having a temperature, is almost a perfect thermal insulator, so it would actually take quite a while to get to the ambient temperature. And in addition to that, the sun gives off quite a bit of radiant heat, to say the least. If the astronaut is exposed to sunlight, he's more likely to heat than cool over time.
posted by empath at 8:43 AM on December 29, 2013

An object in the Solar System would reach an equilibrium temperature that depends on its distance from the Sun, its albedo (reflectivity) and whether or not it's spinning. You can work out the temperature using these formulae. Regardless, the body would be neatly mummified by the vacuum.

UV from the Sun would probably bleach any patches or markings on the suit within decades. I'm not familiar with the materials that suits are made of, or their susceptibility to UV damage, but I imagine they would degrade over time. There would also be radiation damage from cosmic rays and the solar wind. Maybe the face plate would get foggy? Since there's no (regular) wind or rain, though, I imagine the suit would look fairly intact until you touched it, when it would fall apart. (I'm punking out and ignoring the degradation by micrometeoroids, because the flux would depend on where the body is in the solar system, and is not a well-known quantity.)
posted by BrashTech at 8:52 AM on December 29, 2013

One thing that hasn't been mentioned is that the body would be completely desiccated. Because of the extremely low pressure, any moisture eventually just "boils" away.

The temperature of the astronaut would depend on how far away they are from a heat source such as a sun. It is doubtful they'd be so far from anything as to be close to -270C. If its a metal suit, they may even be really hot, picking up radiative heat faster than they can lose it.
posted by vacapinta at 8:59 AM on December 29, 2013

Another thing that hasn't been mentioned is that an astronaut that "floated away" from an object in earth orbit wouldn't proceed out into space; s/he has merely experienced a force that puts him/her into a different orbit. Unless that orbit was extremely high, it would decay over the course of months or years, and a very efficient re-entry cremation would result.
posted by dinger at 10:51 AM on December 29, 2013 [2 favorites]

Apparently bacteria "survived for 31 months in the vacuum of the moon's atmosphere".

Space suits need to handle both heating and cooling: "in the sunlight temperatures might reach 248 degrees F (120 degrees C) and plummet to -148 F ( -100 C) in the shade".

When the astronauts take a leak while on a mission and expel the result into space, it boils violently. The vapor then passes immediately into the solid state (a process known as desublimation), and you end up with a cloud of very fine crystals of frozen urine.

Here's what I think might happen???
1. The suit loses pressure and (since we're ~60% H2O) the body would boil (like the urine)
2. Then the remains freeze (due to transfer of energy into boiling)
3. Unlike the urine, the suit keeps much of the body together
4. Radiant heat melts the body. Bacteria have a party!
5. If the body goes into shade, it freezes. Bacteria are sad for a while.
6. If body goes back in the sun. Goto 4
7. Bones stay largely intact (bones are ~30% water)
posted by sarah_pdx at 11:41 PM on December 29, 2013 [1 favorite]

Upon rethinking, #4 (melting) wouldn't happen. As vacapinta said, at almost zero pressure, water would be solid or gas - not liquid.
posted by sarah_pdx at 11:45 PM on December 29, 2013

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