Viruses are pretty weird things.
They border the line between the living and non-living and seem to only exist for the
purposes of reproducing.
They are simply DNA or RNA strands wrapped up in a protective layer, often hundreds of
times smaller than bacteria.
There are millions of different types of viruses which means that every type of cell-based
life out there can be infected.
And they outnumber every other living organism on Earth by about 10-1.
With all the talk of the coronavirus recently, I started wondering about how a space environment
would affect viruses.
Can viruses survive in space?
Could landing a spacecraft on another world potentially contaminate it with Earth-based
lifeforms?
How do astronauts react to disease while in space?
And also, is a “War of the Worlds” scenario something that could actually happen, where
alien microbes easily infect the host that has no immunity to it?
I’ll tackle the first questions to start with.
Can viruses, or bacteria for that matter, survive in space on a spacecraft, and if so,
could we be contaminating other worlds with Earth-based lifeforms in a process called
panspermia?
When a space probe is being constructed, it is often made in a clean room to ensure dust
doesn’t damage the sensitive equipment.
It’s also to reduce, as much as possible, contaminating the probe with terrestrial lifeforms.
If the spacecraft is only going into an orbit around Earth, germs onboard won’t be such
a big deal because even if the spacecraft was contaminated, chances are that the satellite
will fall back to Earth eventually anyway.
However, probes going further afield undergo a much more stringent sterilisation process
before they are launched.
During construction, each part will be individually sterilised with alcohol wipes.
They then undergo a process called dry heat sterilisation, where the probe is heated as
much as possible, up to a maximum of around 120°c for 30 hours.
This method isn’t always possible though if the instruments onboard are too sensitive
for such high temperatures.
In that case, there are other methods available.
The overall goal from these processes is to reduce the count of bacterial spores on the
surface to less than 300,000, as completely eradicating every single microbe is a near
impossibility.
Polyextremophiles, or a type of extremely hardy bacteria, are known to be resistant
to various sterilisation processes, so they may still linger on the spacecraft even after
the sterilisation process.
Which means once launched, there could well be microbes on the spacecraft that have survived
the whole ordeal and are now in space.
But can they also survive there?
Well, scientists clearly think they can, or the initial sterilisation process would be
pointless.
However, the survivors now need to be resistant to UV radiation, low temperatures and the
vacuum of space.
And once the probe arrives on the extra-terrestrial world, it would then need to find a habitat
to start reproducing on.
So, could this have already happened?
Maybe, although from all these processes, scientists think there is only a 0.01% chance
that we have contaminated another world, or in other words, that panspermia through forward
contamination has happened.
What about viruses?
Well, viruses outside of a host cell aren’t really considered alive to begin with, however
they don’t last long without a host before they are damaged or destroyed.
Most viruses won’t last longer than a week without a host, and that is under good conditions,
let alone the harsh environment of space.
So, if there were no bacteria on the surface of a probe, but a few viruses remained, they
wouldn’t last long in space at all.
Onboard a manned spacecraft is another matter entirely though.
Us humans are a lot more needy than robotic unmanned missions in space, needing a similar
environment to what we experience on Earth.
Unsurprisingly, this is the same environment bacteria and viruses also thrive in.
Humans aren’t really built for being in space, the launch process, the zero g’s,
the artificial habitat, all heighten astronaut’s stress levels, even if they are very good
at coping with it.
A recent NASA study has found that dormant viruses in the astronauts have been awakened
while their bodies were under increased stress, as urine and saliva showed a marked increase
in the number of herpes viruses shedding, or in other words, herpes viruses trying to
find new hosts.
Herpes viruses include oral, genital, shingles and chickenpox.
However, stress being a factor of viral shedding doesn’t really come as a surprise; our immune
systems do a lot better when we are not stressed.
But it does means that right now, in the ISS, viruses and bacteria and reproducing and flourishing.
However, there are lots of filters onboard which clean and recycle the air, meaning that
the risk of these viruses spreading and making the whole crew sick would be reduced.
The study goes on to say that the longer the spaceflight, the more the viruses reactivate.
This is another factor to consider when we want to send humans to Mars which would require
a lengthy spaceflight.
One solution to this would be vaccinations against the viruses, however there is currently
only a herpes vaccine for chickenpox.
So, we’ve talked about panspermia through forward contamination, or in other words,
us bringing microbes to other worlds.
Something that if it hasn’t already happened, will certainly happen if we ever send humans
to Mars.
But what about panspermia the other way, back contamination?
Could there already be alien bacteria or viruses flourishing on Earth right now, or even if
it’s not, is it a possibility in the future?
Well, first of all, let’s discount the possibility of alien spaceships having visited us already.
Let’s just focus on something we know a little more about, and that is asteroids and
comets.
Now numerous missions have been conducted, which have studied asteroids and comets closely.
Some of these missions, like ESA’s Rosetta mission, rather surprisingly found complex
organic compounds on the comets surface.
Compounds like nucleic and amino acids, which are the building blocks of DNA and life.
However, none of these missions had dedicated instruments which were able to detect life,
meaning we still don’t know definitively if there are alien microbes to be found on
comets.
I should note though, that while complex organic compounds are a fascinating find, there is
still a massive gulf between organic compounds and even the simplest of life forms.
Scientists just don’t think that a comet or asteroid can provide the environment needed
for life as we know it to develop, for instance, no atmosphere, no liquid water, no protection
from the Sun.
But let’s say there is life to be found on these objects, and that some of them landed
on Earth, surviving the fall and the atmospheric entry.
Could we be in for a massive problem with an invasive species?
The chances of that are very slim indeed.
Viruses are good at infecting species they have evolved and adapted with.
They are constructed in very specific ways to penetrate and infect very specific cells.
Let’s give a basic example.
Say the alien virus species was much bigger than typical cells on Earth, then they simply
wouldn’t fit into most cells.
And that’s assuming these viruses also use DNA or RNA to spread, in a different environment,
they might have evolved a completely different system, and so would not be compatible with
Earth-based life.
It should be mentioned though, that we are talking a lot about probabilities here.
Even if the risk is low, should we ever send samples of Mars back to Earth, NASA’s protocol
suggests that these samples would be quarantined and studied intensely to reduce the risk of
any back contamination.
So, they clearly aren’t discounting the idea.
A minority of scientists are convinced that back contamination does happen and continues
to happen.
In fact, a paper in Nature called “an Overprotection of Mars” suggested why bother with the sterilisation
of space probes when Mars and Earth have been exchanging space rocks for millions of years?
This is referring to meteor impacts ejecting material into space, some of which eventually
fall onto the neighbouring planet.
So, while panspermia is seen as highly unlikely, we can’t actually prove anything either
way just yet.
Which means I would be very interested to hear your opinion of this in the comments
below!
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