Hey Doc – what’s this I heard that space radiation might have helped form organic molecules in deep space? And here I thought radiation killed living things, not that it helped create them. Huh?
Your confusion is easy for me to understand – when I was learning about reactor water chemistry I learned that the radiation inside a reactor core can disassemble water molecules, which we saw as (among other things) hydrogen gas in the reactor coolant. Then the next day we learned that we needed to add hydrogen to the reactor coolant from time to time to make up for the hydrogen that, when exposed to radiation in the reactor core, would combine with oxygen dissolved in the coolant to form water. Which left me confused – I wasn’t sure if radiation tore water molecules apart or welded them back together. And it turns out it can do both – different types of radiation have different effects on water molecules, and when we say “radiation” it can mean alpha, beta, gamma, or neutron radiation, as well as protons, x-rays, and more. But heavy particles (alphas, neutrons, and protons) have a different effect than lighter ones (beta and gamma); the reason for my confusion was that simply saying “radiation” doesn’t give enough information to know whether it’s a type that will disassemble water molecules or put them back together.
So with your question, the simple-yet-confusing answer is “yes.” Yes, radiation can hurt or kill living organisms and yes, radiation can help to assemble the organic molecules that form the basis for life as we know it (more on this later). The question can come down to what kind of radiation we’re talking about, how much of it there is, and what kind of life is being exposed.
Backing up a little bit, spacecraft orbiting Saturn have made observations of the major moons they’ve encountered. Some of these are icy moons – they seem to be made largely of ice and water with salty oceans lying beneath a frozen covering tens of kilometers thick. But what’s most exciting is that some of our spacecraft can identify elements and molecules by studying the way they interact with light and radio waves. Interestingly, some of these moons have occasional jets of water spraying into space, and many of these jets have been found to contain organic molecules – the molecules from which life (on Earth) is constructed.
We ought to start with what a scientist means when they talk about “organic” molecules; to a chemist (or biologist, or any of a number of other specialties), all “organic” means is that the molecule contains carbon atoms bonded with hydrogen or with other carbon atoms. So carbon dioxide (CO2) is not an organic molecule but methane (CH4) is; organic molecules can be as simple as methane’s five atoms or as complex as proteins that can have thousands to millions of atoms. So when a scientist reports finding “organic molecules” in space (or anywhere else) we’re not sure if they found something as simple as methane or as complex as the proteins upon which life on Earth depends. As a rough rule of thumb, the larger and more complex the organic molecules that are identified, the closer they are to something that was once (or might be) alive. Incidentally, among the organic molecules found in space are the amino acids from which proteins are made.
All that being said – here’s the thing. Organic molecules have been found in plumes of water shooting out of some of Saturn’s icy moons. If the water in these plumes comes from the oceans beneath the ice then this means that those oceans must be laced with these same organic molecules, which means it’s possible that, beneath all that ice, these molecules might have assembled living organisms, even if only bacteria or viruses. But if those jets of water are formed closer to the surface – well above the hidden ocean – then all they signify is the presence of organic molecules in the ice. And that’s what the latest study seems to show – that the organic molecules our craft have found seem to have been formed in the upper layers of the ice by the action of radiation on the elements and molecules contained in the ice.
What the research you mentioned discusses is an Earth-bound laboratory experiment to see if the sort of radiation (ionized water molecules) that some of Saturn’s moons might be expected to encounter can cause simple organic molecules to form the moderately complex organic molecules detected in the water plumes emanating from Saturn’s icy moons. And what the scientists found is that this is plausible – exposure to radiation can cause simple organic molecules to join together to form more complex organic molecules. Which means that simply finding these moderately complex organic molecules doesn’t mean that we’ve found proof of life – it just means we’re (maybe) a little closer.
In a sense this is sort of frustrating – it’d be nice to be able to say “Wow – organic molecules! There’s life out there!” But that’s a little too easy – and important questions don’t necessarily have easy answers. And it’s important to do this sort of thing – if only so that every observation that might reveal the presence of life be rigorously and exhaustively tested and, if possible, shot down. Only by doing this – by trying to find an unexciting reason for discoveries that might indicate the presence of life – can we be sure that, when scientists generally agree that we have found evidence of life somewhere “out there,” that it’s likely to be true. As Carl Sagan noted, “Extraordinary claims demand extraordinary evidence” and announcing the discovery of life anywhere other than on Earth is certainly an extraordinary claim that demands scrupulous examination before it can be accepted.
And that brings up one other point – we’re very good at understanding “life as we know it” – life that requires liquid water, organic chemistry, moderate temperatures, and all the other factors thought to have contributed to life’s arising and surviving for four billion years here on Earth. But we have no idea what other forms life might take, and it’s entirely possible that we might not even recognize “life as we don’t know it” if it joined us for breakfast. There are all sorts of learned discussions about why carbon is essential, why there must be liquid water, and so forth – all coming down to why, since there’s life on Earth, only a planet exactly like ours can host life (or, at least, intelligent life). The problem is that this is sort of like trying to figure out how to win at roulette by studying a single spin of the wheel.
Think about it – say I’m trying to get an edge in roulette so I watch one spin and measure everything about it, then try to figure out why the ball landed in slot 14 instead of one of the 36 or 37 slots. We might look at the position of slot 14 at the exact instant the ball was released, the speed of the ball, the speed of the wheel, and any other parameter we feel relevant. We might check to see how tight (or loose) the dividers between adjacent slots are, look for minute differences in the dimensions of the winning slot – whatever we can think of to find out why, on that one spin, slot 14 was a winner and every other slot was a loser. Similarly, when we look at the one place in the universe where we know that life exists we’re tempted to say that the conditions here must be the only ones that can give rise to life. But that’s just our best guess – until we can find life elsewhere and confirm the conditions under which it appeared and thrived, we can’t really differentiate between what we have here on Earth and what is absolutely necessary for life to exist at all.
In any event, the work you read about doesn’t mean that there’s no life in the ocean of any of the icy moons in the outer solar system – it just means that there are ways to form these organic molecules that don’t depend on the presence of life. One of these days (we can hope), we’ll be able to go out there ourselves to find out for sure. And we can comfortably say that we have not proven that life requires radiation to form, nor that the presence of radiation makes the existence of life impossible.