On its face, carbon monoxide is an extremely dangerous gas, at least to humans.
There are two reasons for this, one, given that it’s toxic to humans, it’s also somewhat
insidious in that it has no color or odor leading to easy accidental poisoning in people
exposed to it.
The other is that it’s chemically active within the body, which is what makes it so
toxic, essentially making the body unable to distribute oxygen.
Up until now, it’s been assumed that if carbon monoxide were detected in the atmosphere
of an exoplanet, it would indicate that life probably did not exist there, at least as
we can envision it.
Not only because it can be outright poisonous to some biology, it would also serve as a
ready source of carbon and energy for any life that can use it.
Thus it was thought it wouldn’t stick around long in an atmosphere with microbial life.
But this is being rethought in a broader context.
Are some assumptions we make about certain things that would seem to preclude life from
existing on an exoplanet not as set in stone as we might think?
In a paper by Edward Schwieterman and colleagues, link below, they modeled hypothetical exoplanet
atmospheres that contain carbon monoxide and found two interesting scenarios where life
and carbon monoxide in high amounts might co-exist, and that may have been the case
here on earth long ago.
With earth, carbon monoxide doesn’t persist in the atmosphere very long, being destroyed
by chemical reactions.
But this may not always have been the case.
Before the great oxygenation event, there was little oxygen in earth’s atmosphere,
and the sun’s luminosity was less than it is today.
If there were higher levels of carbon monoxide at the time and conditions here allowed it
to build up more than today, it would have been maintained when simple life was everywhere
on this planet.
If that could happen here, then it should be possible on exoplanets.
But there’s another scenario that came from the modeling, that might be even more interesting.
In a planetary system centered on a red dwarf, such as the Trappist 1 planets or Proxima
B, it may be easier to create and maintain carbon monoxide, and that oxygen rich planets
with high abundances of carbon monoxide, could also host life.
That these possibilities exist calls into question the so-called antibiosignatures at
large, which are a group of atmospheric scenarios that would rule out an exoplanet being inhabited
by life.
For example, Venus.
Normally, this would be the last place one would expect to find life.
If Venus were a distant exoplanet, the crushing heat and pressure would probably preclude
it from being considered a candidate for a world inhabited by life.
But, the specific conditions Venus was subjected to over the course of its history changes
that equation.
Venus is suspected to have once been very different, possibly a water world like earth
for a time earlier in its history.
If this was the case, then that’s the first criteria for earth-like microbial life to
have its genesis.
If that life adapted to the changing conditions of Venus, it’s possible that it could still
be there high in the upper atmosphere where conditions aren’t anything close to as harsh
as that of the surface.
Another example is Jupiter’s moon Io.
Again, this wildly volcanic radiation bathed moon wouldn’t intuitively be considered
as a candidate for microbial life, but it actually is one.
Io once had as much water ice as any of the other galilean moons of Jupiter, and deep
down may still have small amounts under volcanically heated conditions.
While a huge long shot, in fact probably the longest shot of all the candidates for microbial
life in the solar system, it is in principle possible for life to be eeking out a living
deep down in a moist, warm Io lava tube.
These kinds of scenarios where a body’s unique history gives inroads for life will
make it very difficult to definitively rule out life on some exoplanets that might otherwise
seem too harsh for it.
Life on earth has proven to be ridiculously resilient and adaptable once it gets a foothold,
particularly the microbes, so it may well be that only the harshest antibiosignatures
can be used to definitively rule out of the possibility of life on certain exoplanets
in the universe, even ones rich in gases like carbon monoxide.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently musing about ANNA
and my personal carbon monoxide factory, the le baron.
She thinks it would run more efficiently on hydrogen, which is highly flammable, but I
would prefer to remain alive and be sure to check out my books at your favorite online
book retailer and subscribe to my channels for regular, in-depth explorations into the
interesting, weird and unknown aspects of this amazing universe in which we live.