Thread by @mike_malaska

Are viruses alive?
(Here is the thread y’all have been waiting for….)

Our survey says…..Yes! They are!

What do I think? Mmmmmm. No. they are not….well..sorta.
But no.

Digging into the big #science questions of #astrobiology
(Thread)

Definition of life is pretty fuzzy. Seems like its easy “yes or no” but IMHO it’s a big wonderfully complex beautiful spectrum. And by thinking about it, and how we would measure it, we can make better tests for detecting “life” on alien worlds, with alien biochemistries.

Here is a great link on “life” from NASA Astrobiology: nasa.gov/vision/univers…

And like any “working definition”, when new discoveries get made, we can “Pluto” it. By that, I mean change definitions to help classify all the new things we discover – including things that don’t fit.

An example is that we "currently" know that there are many kinds of worlds: rocky planets, gas giants, ice giants, dwarf planets, icy bodies, Ocean Worlds, Hydrocarbon Worlds (looking at you, Titan.), etc….

And there are some worlds that don’t fit our definitions: rocky bodies that vent like comets, then go quiet again. Is Ceres an Ocean World, a Dwarf Planet, or a Mud World? Complicated.
(Nice open-access article on Ceres here by Julie Castillo-Rogez: liebertpub.com/doi/full/10.10… )

For the “living or not” question, maybe it’s easier to start with the ends of the spectrum (as we know it so far) and try to work inwards. For now, we’ll take a basic definition that life is catalyzed chemistry, that is able to replicate, transfer information, and can evolve.

(This narrows out a lot of things. But our current instrumentation and ideas are good at detecting molecules. "Go with what you know.")

So we can start with a dead thing, that moves chemical energy, and replicates: crystals of table salt. If you take concentrated salt solution, and sprinkle crunched up salt crystals in it, it will crystallize out.

So the little pieces nucleate (or seed) new salt crystals.
Some crystal making fun here: learning-center.homesciencetools.com/article/crysta…

You’ve gone from a solution to crystals, so you’ve done a phase transition. Is it really “chemistry”? well yah (sorta), going from solution to solid the sodium ions are now with ionic bonds next to chloride ions instead of water molecules.

Did it reproduce? Well, you started with tiny salt pieces, and now you’ve got a jar full of crystals. You could take those and seed more…. Did it transfer information? Well, not much. The atoms are in a regular alternating lineup. So there's a repeating unit, but always same.

Here is a nice clip showing the beauty of crystal growth (with piano):

Can it evolve? No!…well, maybe….If you cool salt solution down below 0, it comes out not as NaCl, but as NaCl with a water molecule attached (called hydrohalite). This is chemically preferred, so did the salt adapt to the new conditions? MMMM…..arrrrrggghhhhh….prolly no?

Link to Wikipedia on hydrohalite: en.wikipedia.org/wiki/Hydrohali…

So. Even looking at the simple “dead” salt case, we need to go into a “yah but….” mode, and exclude regular crystal molecule/ion arrangements as information, and new crystal phases as adaptation and “evolution”.

You may ask: is the crystal formation competitive??? Google up “crystal polymorph pharmaceutical”. Once you get a bad crystal form (polymorph), it can win out over all the other crystal forms. It's a mini evolution experiment with only a few states, but one wins and propagates.

Could crystals ever actually ever be “life”? Uhm. Yeah. I think so. We’ve kicked around some ideas of solid phase life. You could have a single molecule with many polymorphs spatially arranged to make some type of coded structure. (think of a 2D barcode, but with molecules).

Like this: en.wikipedia.org/wiki/Barcode#/…

It would need to be catalytic, and carry information that doesn’t always perfectly copy, so it can evolve and get better (or worse) in terms of catalysis or any other functions. You’d need a sea of building blocks, or things that could be built up to become building blocks.

This is where you could start thinking about really funky things like mixed metal life etc. What instruments would we use to find these? Most of our typical stuff for spacecraft missions would be useless.

We would need some hardcore way of detecting spatial arrangements of atoms and molecules at super-tiny scales (molecular or even atomic scales.)
(SciFi authors feel free to riff off these ideas.)

Which gets to the next question: how do we look for life anyway? The basic idea astrobiologists use is to “look for funky things you don’t expect.”
“Hey, why are these complex amino acids here? I don’t expect that!”

“Hey, why are all these molecules in the chiral S form? I don’t expect that!”
“Hey, why is the stable isotope ratio here so goofy? I don’t expect that!”
“Hey, what is this funky complex shape looking thing doing here? I don’t expect that!”
en.wikipedia.org/wiki/Diatom#/m…

And if we saw something like this under the microscope on an alien world?
en.wikipedia.org/wiki/Naviculal…
You’d have a rough time explaining that away as a chemical or physical process (but you’d have to try.)

So let’s go to other side of the spectrum. Something definitely alive. We always teach the idea of a single isolated cell surviving in the wild by eating some chemicals or harvesting light and not needing any friends.

How about one of my favorite microbes Shewanella oneidensis?
en.wikipedia.org/wiki/Shewanell…

IT EATS METALS! HOW SERIOUSLY BAD-ASS IS THAT???

But…what about microbes and other critters that don’t do so good by themselves? Some microbes are connected up with other microbes in a community. “It takes a village”. By themselves, not-so-good. Buddied up. All good. Are these alive?

Mmmmmmaybe...OK. yah, sure. But evolution/adaptation and information transfer all kinda messed up in a not-so-clean-and-straightforward story.

(Stuff they don't teach you in Biology 101 coming up...)

Want a real wild ride? Buckle up, we’re gonna talk about about Wolbachia - a bacteria that is a parasite of arthopods.

Per Wikipedia “Some host species cannot reproduce, or even survive, without Wolbachia colonisation”

en.wikipedia.org/wiki/Wolbachia

Say what?

Yeah. You read that right. Some Insects cannot reproduce without Wolbachia bacteria riding along.
Wolbachia could parasitize up to 70% of all insect species (one of most dominant forms on life on planet).

“SO ARE YOU TELLING ME COULD BE RESPONSIBLE FOR THE REPRODUCTION AND EVOLUTION OF SOME OF THE DOMINANT LIFE FORMS ON PLANET EARTH?”
Yup.
They definitely did not cover this in sex ed. The Birds, the bees, and Wolbachia driving the bus.

The evolution we were taught in basic biology is pretty much BS (strike 1).

So are those host insects alive? (not by themselves, if no reproduction then game over) And the Wolbachia (well, maybe, sorta). If we isolated and examined either item we don’t get the whole picture. As someone in the poll comments said, we need to understand the whole ecosystem.

And our spacecraft mission instruments just aren’t designed to “understand the whole ecosystem” and disentangle all the relationships. We'd have to deal with the bulk, assuming the bulk is all right where we sampled.

How about hardcore parasites that MUST have a host to reproduce. Are they alive? Well no, not without the host. Or hosts. It takes a village.

(but not every individual in a village is helpful. some are parasites.)

This is where we can start also thinking about the origin of life. Did RNA come first? Membranes? Proteins? Inorganic catalysis? I personally think that way to simple a view.

Let's stick with that idea of community. This thing here makes A-->B. The thing over there goes B-->C. Over there C-->D, which is needed by the thing that makes A-->B. Village.

So maybe at origin of life, you had separated functions. A-->B waaaay over there (hydrothermal vent, say). And B-->C in that evaporating pond on surface. And C-->D in sea ice during freeze jacking.

At some point, functions got combined. Closer, proximity, faster. More competitive. Not sure when cells kicked in, or if the cells were complete units. Could have been mutualistic. Who knows? (I wasn't there.)

Same thing could happen on other worlds. Especially in nutrient poor, low temperature environments where geology/diffusion happens faster than catalysis. You may have localized spots that are good at one process. We should be thinking about that.

In that case only a few of "life-check" boxes could work on an astrobiology mission. Other limiting nutrients and processes (that work better elsewhere) may fall below instrument detection limits.
"Here is where we make the phenylalanine."

So...now to viruses. Are they alive? They have information. But they can't reproduce by themselves. They can evolve, but they need a host. So by themselves. No. They are not alive. As part of a community, yes.
I'd give them a 2/5.

(they get bonus points for sometime carrying and coding for their own machinery.)

How about prions? Bad protein crystal forms. They aren't really part of a community. They can't evolve. In most cases you need to have a host protein that started out and went bad. Propagated out the defective form by converting the other proteins into prion form.
So 1/5.

They don't get high points because no evolution. But I'll notch them up above table salt because they did start as a protein made by a living critter. So it a signal (biosignature) that 'something' out there is alive.
Just not the prion.

Now...imagine a minimal set of linked molecules. Maybe it formed randomly and naturally. Bends itself into an-ever-so-slightky autocatalytic form. Think of it as a prion-plus.

Autocatalytic but not perfect. Sometimes it gets a little better. This getting interesting, right?
It's the idea of a protein world.

Or if RNA which can be autocatalytic. Is now scoring much higher in our life-score. But still missing bits. Maybe no cell wall, no energy carrier.

So that's the idea of an RNA world.

Can imagine alternant scenarios. What if instead of genetic information packaged in virus, it's catalytic? So viruses help cells they infect by making more efficient. More efficient more viruses (till "pop" game over.)

I'm convinced there are a lot of weird scenarios that we can even think of that are out there. Might need to rethink how we look, define, and explore.and develop tools to just look for weird stuff.