Theoretically, how long could microbes survive on a spacecraft?

There was a study a few years ago which concluded that frozen, desiccated, Deinococcus radiodurans could survive on Mars for almost 300 million years if they were buried ten meters below the surface. However, they were only chilled to -63 degrees Celsius and the ship would get much colder than this. But they were exposed to UV, gamma rays, and high-energy protons, which would likely penetrate a drifting ship.

So, it's conceivable microbes could survive six million or so years in a spaceship, and they might even survive atmospheric reentry, that ship looks big enough.

No comment on the microbes, but that movie definitely left me with a dreadful feeling. It’s been a while since I saw it, but probably not one I’ll rewatch although I thought it was pretty good.

We don't know the upper limit.

If sufficiently shielded from ionizing radiation (a metre or six of regolith ought to do it) then a quarter of a Gyr appears to be tolerable by at least one flavour of psychrophile.

https://www.bioprocessonline.com/doc/250-million-year-old-bacterial-spore-comes-ba-0001#:~:text=Researchers%20from%20West%20Chester%20University,cavern%20in%20southeast%20New%20Mexico.

Some microbes can survive for millions of years, so yes they have a chance. It’s the entire premise of the pan-spermia theory.

My guess is that one day we'll discover microbes on a comet

In terms of temperature and chemical stability it seems at least conceivable that a microbe in some frozen dessicated stasis could remain viable for millions of years - but interstellar space is filled with various forms of radiation that would almost certainly obliterate complex organic molecules over that timeframe unless they were very carefully shielded.

So... Probably not in that scenario. A mars bound vessel would not be built with that level of shielding, as it would be designed to keep humans reasonably safe from dangerous radiation exposure for ~6 months - not six million years.

The analogy is deep rock microbes on Earth. In nearly every place geologists have drilled miles deep holes in rock, microbes have been found if the rock temperature has stayed below 250 degrees F. Some of these microbes may have been buried in such rocks for tens of millions of years with minimal food sources.

I heard the mir station developed a rather nasty internal biome

Just props for mentioning one of my favorite movies of all time (though my wife wasn't as enthused as I was). Easily in my top-ten.

One note though, on the ending: Aniara doesn't collide with anything; it either passes or enters the orbit of an earth-like planet.

Some bacteria survived on surveyor 3 on the moon's surface for years. Some microbes, it seems, can do well in space. 

NASA has a job specifically for this to make sure we mitigate contaminating the solar system while searching for life.

Gee, I am so glad I bailed on that movie 20 minutes in. I had a bad feeling about it.

A study done on patients in a nursing home showed residents who lived in a certain room kept catching the same illness over and over again (different residents would move in, get sick). The bacteria was linked back to the very first resident who fell ill with it seven years prior. They found it on the door knob. It was proven to be the same organism after testing was done.

2 1/2 years inside the solar panel of Surveyor 3 that Apollo 12 brought back from the moon.

There is really not a straightforward answer for this

First, how do we define survival?

Defining death is much more difficult for microbes than humans, and there is still the occasional person that wakes up in the morgue. Meaning that they were declared legally dead but they weren't.

Viable but nonculturable is this whole controversial subject, that people even argue about the definition of.

Then 99% of microbes don't have defined culture conditions.

There are ways to detect microbial metabolic activity without culturing them (that have metabolic activity we can test for), but spores aren't metabolically active.

There are many many species of microbe that are living their best lives in the environment or taking a nap (sporulated) that we can't prove if they are alive or dead.

Very few microbes can infect people in a noticeable way, or even live as commensals on our skin even transiently. If any particular thing is alive, it isn't very likely it would cause us as much as an itch. I'm not saying it isn't a possibility, just that the odds are very low on an individual microbial species.

Anyway, yes, it isn't implausible that a spaceship crashing into an earth-like planet after 6 million years could have a chance at altering an existing biosphere. We might not be able to grow it in a lab on earth,and it might not be able to grow in or on us.

Not an easy question to answer exactly. But 5+ million years of radiation exposure is going to get everything. Spores are the hardiest thing bacteria make but they are not invincible. So sort of depends on where the craft is, how much radiation it is exposed to etc. but with enough radiation those spores will be killed. If the craft gets a lot of radiation in a short time it would be sterilized pretty quickly. If it is a lower level of radiation over a longer time it will take longer. I think you would be hard pressed to find anything alive at 50k years, but would probably be even faster than that. Regular, growing bacteria, that is non spores would only survive as long as there were nutrients and proper conditions for growth so those are not going to last long at all unless you have tried to set up some situation where they could survive longer. I haven't seen the movie so am sort of assuming it is just a regular space ship and not something designed to protect spores as long as possible.

I’m just commenting so I can come back to this post when someone more knowledgeable answers. Super interesting question!

For the rest of their life. Just like you and me. Haha

It is very reasonable to believe that some microbes would be able to survive within the ship, despite the conditions. Sounds like a good premise for a sequel haha