We are generally not big fans of viruses right now, but we sure are thinking about them a lot.
That’s right, even astrophysicists are pondering these bizarre little critters.
In fact astrovirology, although very new, is actually an emerging subfield of astrobiology.
And that’s because it turns out viruses don’t just influence organisms - they’re
incredibly important on a planetary scales.
Perhaps an interplanetary scales.
There are far more viruses on Earth than all cellular organisms combined, and so they drastically
affect our entire biosphere.
And it’s increasingly believed that they are critical factors in the process of evolution,
perhaps even in pre-cellular days.
That’s right, viruses or their ancestors may have played a role in the origin of life
on earth, and may be needed to initiate life on any planet.
Oh, and astrovirology is also concerned with the possibility that viruses can travel between worlds.
I’m going to start with this absolute statement, because you know how the internet can be.
The new coronavirus - Sars-CoV-2, the virus that causes COVID-19 did absolutely not
fall to earth from space.
I’ll come back to how we can be 100% confident of that, a bit later.
First up, let’s talk viruses generally.
But let me preface this by stating the obvious - astrophysics channels are not the best place
to learn virology.
I want to do this review to highlight the details of viruses that make them important
on a planetary, and even interplanetary scales.
Viruses sit on the blurred line between living and not.
They contain genetic material - either single-strand RNA or double-strand DNA - and when not active
inside an infected cell, they surround themselves in a protein shell - a capsid.
We often think of a “virus” as this bundle of genetic material within a shell, but the
term for that bundle is a virion, and this is more of a transport mechanism for the genetic material.
The term virus better describes the entire microbal lifecycle, and inside an infected
cell, a virus has no shell - it is the genetic material.
Unlike cells, viruses do not metabolize - so they don’t produce their own energy, and
they can’t reproduce without coopting the reproduction machinery of a cell - hence the
dispute over whether they can be called “alive”.
One thing viruses do share in common with life is the ability to evolve.
Their extreme numbers and reproduction rate means rapid evolution.
As well as resulting in the vast array of existing viruses, this means some viruses
produce new strains every year.
That’s why you need a new flu shot each season.
But viruses aren’t just masters of their own evolution - it seems they may be an essential
driver of the evolution of cell-based life.
Because viruses insert themselves into DNA to reproduce, they are actually able to transfer
genes between organisms.
Viruses are the original genetic engineers.
And some of your own most useful genes were left in your DNA by a virus that infected
an ancestor.
As well as driving cellular evolution, viruses may have been critical in the formation of
cells in the first place.
For a long time it was believed that viruses evolved as escapees from DNA-based cells,
but more and more virologists think that viruses may predate cells.
RNA-based viruses in particular may have emerged from the pre-cellular RNA world, which would
make them our most distant cousins on the tree of life.
Or tree of "life"?
And pushing their gene-transferring powers that far back means they may have massively
accelerated the evolution that led to the development from RNA-based pseudo-life to
the first true DNA based cellular life.
Understanding viruses may be the key to understanding the origin of life.
The extreme abundance of viruses on Earth, and their critical role in evolution and possibly
even abiogenesis, suggests that we probably should be thinking about whether there are
viruses on other worlds.
One of the most promising prospects for our first detection of alien life is to find signatures
of its chemical activity in the atmospheres of alien worlds.
We’ve talked about how this is done before - but in short, when an alien world passes
in front of its home star, we can see signatures frequencies plucked from the starlight due
to it passing through that planet’s atmosphere.
Cellular life massively alters the atmosphere because it excretes gases - oxygen, methane,
nitrous oxide as that light metabolizes.
But viruses don’t metabolize, so won’t leave direct atmospheric biosignatures.
But what about finding viruses in rocks that fall to Earth?
Well because they’re so tiny, they aren’t likely to leave distinguishable fossils like
bacteria can.
Nor do they leave biosignatures in those rocks.
That means the remnants of dead viruses are unlikely to be found in meteorites from other worlds.
So the evidence of alien viruses is unlikely to come to us.
We’ll probably have to go out to look for it.
The first stop in our search for life is always Mars.
The red planet seems pretty dead these days, but it’s conceivable that an ecosystem of
extremely hardy microbes lives beneath the Martian surface. And some viruses are among
the hardiest of all microbes, so it might pay to look for the signatures of viruses
as we continue to explore Mars.
Perhap more promising are the ocean moons of the gas giants.
Jupiter’s Europa and Saturn’s Enceladus these are known to harbour vast oceans beneath
their icy surfaces; oceans kept warm by the tidal flexing caused by their parent gas giants.
If those oceans contain microbial life, then they may also contain viruses.
Both Europa and Enceladus spray geysers of ocean water into space that can be captured
by probes.
Again, specialized instruments on future missions could detect viral material.
OK, all this talk of viruses hitching rides into space brings us to our last, and most
sci-fi-horror-movie relevant point.
Can viruses from one planet infect another?
There are two parts to this question: can a virion survive an interplanetary journey?
And then can it actually do anything when it arrives?
The answer to the first part is definitely sort of maybe.
Like I said, viruses can be carried by tiny water droplets.
Earth’s upper atmosphere is thick with bacteria and viruses - mostly swept into the atmosphere
from the oceans by seaspray.
From there they can travel across the globe, but also perhaps be lifted into space.
Very light droplets can be lifted to the very edge of an atmosphere with the help of the
planet’s magnetic field and then swept into interplanetary or even interstellar space
by the radiation from the star.
This is radiopanspermia, and it’s a compelling way to transport viruses because the mechanism
is especially effective for very small water droplets - of the kind that viruses tend to
occupy.
In fact it would be surprising if there were not quite a lot of viral and other microbial
material riding the solar wind into interstellar space.
So yeah, stars sneeze, you might want to maintain 6 light years distance.
Viruses can also be launched into space embedded in rocks that are ejected in asteroid or comet
impacts.
This is lithopanspermia, and again - virus-ridden rocks have definitely left the Earth before,
and probably impacted other bodies in our solar system.
Earth certainly gets hit by rocks from Mars - so if Mars ever had viruses then some of
that material may have reached Earth.
Virus-bearing rocks from worlds beyond our solar system are possible, but those viruses
would need to remain viable for 100s of thousands to millions of years.
And it's the ability of viruses to survive long spaceflight that becomes the real question.
Outer space is deadly - it’s a freezing cold vacuum bathed in intense radiation.Virions
are a bit like seeds or spores - dormant until they come into contact with their prey.
And like seeds or spores, some virions are remarkably resilient.
Take the tobacco mosaic virus - it can actually be crystalized, protecting it from desiccation,
cold, and vacuum.
In fact that particular virus has survived being bathed in the equivalent of 250 years
of cosmic rays, simulated by an intense shower of energetic protons.
Polioviruses and bacteriophages have stayed infectious after space-like environments of
high-altitude balloon and rocket rides.
Some bacteriophages have also shown resistance to UV exposure in experiments on the international
space station, however their viability after that exposure hasn’t been tested.
Some viruses do have the remarkable ability to sort of reassemble their genetic code after
irradiation by UV or cosmic rays.
Even if most individuals within an infecting population have damaged genes, as long as
the full, correct virus genome is represented across the population within a given infected
cell, the viral genome can be reconstructed as the virus replicates itself.
All of that said, radiation from stars is probably our best hope for obliterating
space viruses.
Beyond a certain point, a damaged genome renders a virus non-functional and can’t be reconstructed.
It’s likely UV exposure would destroy most viruses trying to hitch rides via radiopanspermia
- and that’s good, because that’s the only known way to really spread LOTS of viruses
between planetary systems.
Lithopanspermia can spread vastly fewer microbes, but it’s more reliable because a barrier
of rock or ice will shield against ultraviolet light and cosmic rays.
OK, so we’ve established that there’s at least a remote chance of interplanetary
or interstellar viruses making their way to Earth.
Or Earth viruses going back the other way.
But are such alien lurgies really a possible danger?
In order for a virus to infect a cell, the virus needs to bind with receptors on the cell’s
surface and then integrate its genome into the cell’s DNA.
Different viruses have evolved to infect a vast array of different cells, and some even
infect other viruses.
But one thing they all have in common is that viruses all infect life as we know it.
At the very minimum, a cell needs to be DNA or RNA-based to be susceptible to earth viruses.
Would alien viruses have evolved to attack the same genetic structure?
That would only be the case if DNA/RNA based life was the norm for extraterrestrial life.
And we have no idea whether that’s the case.
Perhaps DNA is the only possible basis for complex life, or perhaps panspermia seeded
DNA-based life and DNA-preying viruses across the galaxy.
But it’s very likely that an alien virus that made its way to earth would find it had
absolutely no way to attack the cells it finds here.
Let’s get to the last pressing question, which is also the easiest.
Could any of the past recent pandemics have resulted from alien viruses?
No.
We can trace the origins of viruses by their genes.
Take the SARS-CoV-2 virus - it shares the overwhelming majority of its genes with coronaviruses
found in populations of horseshoe bats - and the philogenics - the evolutionary path - is
consistent with it evolving out of that population.
Same with other epidemic-causing viruses like ebola and the spanish flu.
It’s never aliens if there’s a sensible earthly explanation.
But like I said - this is an astrophysics show, so I’ll add some links for more expert
analysis of the virology in the description.
In the meantime, please stay safe from the current very terrestrial virus outbreak, and
at least appreciate this: we are now MUCH more aware of the importance and danger of a
hidden world that has always lived alongside us, driven our evolution, and perhaps predated
life itself - the world of viruses, our currently not-so-favourite, but still fascinating fellow
denizen of space time.
Last time we explored the possibility that the existence of hidden extra dimensions might change the law
of gravity on the smallest scales, and we saw how the 120 year old Cavendish experiment
might reveal those dimensions.
Long story short - it hasn't yet, but the search continues.
Krunoslaf Sokic asks how we can know the inverse square law for gravity holds on the cosmic
scales if we haven’t explained dark matter yet, which originated from the apparent failure
of the inverse square law in the first place.
In other words, maybe the inverse square law breaks down on large scales, producing the
illusion of dark matter.
So people have investigated this in great detail actually.
The theory is modified newtonian dynamics - MONDS - in which gravity doesn’t drop
off as quickly as the inverse square law when you get to very large distances.
Two issues with this idea: MONDS fails to get rid of the need for all dark matter.
Some invisible mass is still needed, and so that eliminates a lot of the elegance of
the idea.
Second, we have other evidence of dark matter - for example in gravitational lensing,
in the cosmic microwave background speckles, and in things like the bullet cluster where
it seems like that the dark matter is separated from the stars and therefore can’t be
due to just having the wrong theory of gravity.
Now A few of you had a really interesting insight - I said that when the masses of the
Cavendish experiment are very close together, you need to factor in the Casimir force between
them to get an accurate measurement of the gravitational force.
So what if the Casimir force itself IS a modification of the gravitational force on tiny scales?
Well the Casimir effect is thought to be due to an alteration in the vacuum energy between
a pair of conducting surfaces, which leads to those surfaces being attracted to each
other.
So why couldn’t it be an increase in the strength of gravity?
Well it’s because you would then expect experiments to measure a Casimir force that
has a simple dependency on the mass of the two plates and their separation.
But that’s not the case.
The Casimir effect depends strongly on the material of those plates - its conductive
and dialectric properties, as well as the geometry of the plates, and for the most part
that dependency agrees with so-called lifshitz theory, which is based on this altered vacuum
energy hypothesis.
CastleKnight7 asserted that Gravity, as with all forces is created by consciousness.
Well I’d accuse you of propogating quantum woowoo, except that this theory is actually
supported right at the top.
The experimental physicist wile-e-coyote demonstrated this on multiple occasions.
And I believe the great Douglass Adams that had a similar hypothesis.
Remember in one of the later hitchhikers guide books when Arthur Dent figures out that the
secret to flying is to throw your self at the ground, and at the last minute get distracted
and miss?
I believe the full theoretical framework was published eminent science journal The Onion
- it’s a refutation of mainstream gravity called Intelligent Falling.