In a week when some pretty high profile stories got some less notable corrections (no, cell phones are not giving young people skull horns and no, we have not convincingly transmitted autism to mice via microbiome transplants), I thought it might be a good idea to try to get ahead of the curve on a new story. This one involves a topic likely to be of greater interest to the science & faith community: life on Mars. Last week, the Curiosity rover detected a plume of methane on Mars in a higher concentration than previously observed. If you had a chance to watch and/or listen to the BioLogos Conference presentation on origin of life and life on other planets (which is now free to view), you have some context for this news. If not, let me try to get you up to speed so you can understand what this observation does (and does not) mean.
“Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” So writes Douglas Adams, and he’s not wrong. Because space is so big, getting into a spaceship and traveling to meet our neighbors in another solar system would take far longer than a human lifespan at the kinds of speeds we can reach now. Sending a friendly text would still take almost a decade round trip. That’s all just to the nearest star, and we have no idea if anyone actually lives there or anywhere else but here. Fortunately, other planets have already been spending millenia sending us messages–not text messages (as far as we know), but reflected and emitted light. And it turns out that light can tell us something about the chemistry on other planets, because different kinds of atoms and molecules emit distinct patterns of colored light.
Planetary chemistry, in turn, can tell us something about biology. Take oxygen, for example. Oxygen is the third most abundant element in the universe, after hydrogen and helium. However, oxygen is a chemical extrovert; rather than be alone with itself, it will react with many other elements, often in a thermodynamically favorable way that releases energy rather than requiring energy input. This is the essence of fire. So most of the oxygen we see out in the universe is bound up with other elements into molecules like water. But here on Earth, we have a lot of oxygen in our atmosphere hanging out by itself, not because Earth oxygen is shy, but because plants and algae and other photosynthetic organisms are constantly making more to replace what reacts and becomes water and carbon dioxide and such. So we think an oxygen-rich atmosphere is a pretty good indication that a planet at least has some kind of photosynthetic life, even if it is only cyanobacteria.
So scientists have been thinking a lot about what to look for in planetary chemistry that might suggest life. Methane in the right abundance is part of that planet-scale signature of life. At the same time, there are other ways to get methane besides living organisms. It is even possible that the gas was made by bacteria but then trapped underground only to be released now, maybe long after the bacteria died. So methane, even methane plumes like this one, is not by itself proof of life on Mars. It is exciting for Curiosity scientists, and it does warrant further investigation. But don’t bake that batch of neighborly cookies just yet.
Just so we’re clear, if we do find life on Mars it will almost certainly just be microbial life. There is no photosynthesis on the surface and no liquid water on the surface. Microbes can tolerate a wide range of conditions, so they could be thriving underneath the surface somewhere, but probably not Martian fish or mammals or Marvins. And actually, even if we do find life on Mars it may not actually be Martian, strictly speaking. We’ll have to check to make sure we didn’t accidentally track bacteria there on our robotic “shoes.” To avoid that scenario, every effort is made to sterilize the probes we send, but it can be challenging to guarantee they are 100% gone precisely because microbes are so hardy . For example, bacteria like Deinococcus radiodurans can survive sterilization procedures like gamma radiation bombardment (pretty incredible, wouldn’t you say, Hulk?).
And while space may be big, it is not as empty as you might think. Space is dusty, and some of that dust is from Earth. Some of that Earth dust could be harboring bacteria like Bacillus subtilis, which has survived reentry into Earth’s atmosphere. And not on the cozy inside of the spaceship either, a stunt not even Chuck Norris could pull off. So even if we did not bring bacteria to Mars on a spaceship or probe, any bacteria we might find there could still have ultimately originated on Earth. We don’t know how likely that is compared to the possibility of life starting independently on Mars, but it is an option that will definitely be explored should we find bacteria there.
Since bacterial colonization-via-dust could have happened 100 days ago or 100,000,000 years ago, we may never be able to get a definitive answer about whether it is truly Martian life or ex-pats from Earth. A similar genome to a known terrestrial bacterial species would be very suggestive of colonization, and recent at that. But what if we find a genome with minimal similarity to anything we know? It could mean the Martian cousins departed a very long time ago, or it could mean they never were here to begin with. For that matter, it could also just mean we haven’t searched enough on Earth for their closest relatives; there are plenty of undiscovered microbes right here at home. So even the very remarkable finding of life on Mars still wouldn’t necessarily answer our big questions about how life started here or how easy it is for biology to emerge from chemistry. And it definitely won’t answer questions about how or even whether God fits into that picture.
So, to sum up: No life on Mars yet. So far, just some methane, which is interesting and exciting because it could be bacterial burps, but also could just be some non-biological chemistry or geology. And no matter which way it goes, scientists (with good reason) will just have more questions and more to study and probably still won’t be able to give you the simple answers some want to all the fun questions about life, the universe, and everything.
Good news for folks who like to read about science & faith via physical media! A collection of STEAM grant-funded posts from this blog have been edited and expanded with discussion questions and compiled into a book. Our own Hannah Eagleson did the editing, and our friends at Hendrickson did the publishing. Pre-order details can be found here. The book comes out in October. Each post features a scientist or theologian addressing a question submitted by students, so you’re getting the perspectives of experts on topics relevant to young people today. And in a format designed to foster discussion. Sounds like a great resource for students and those who minister to students–almost like someone (not me) had a plan.