Ricardo Lopes


What if we found life on Mars?

A week ago I gave a lightning talk at FutureLearn called “What if we found life on Mars?”. It’s a highly speculative theme, outside of my usual discussions around tech and software development, but one that I find particularly fascinating. So I thought that it would be a good idea to bring that talk’s ideas into a blog post format.

Recently we’ve been greeted with exciting news: Curiosity rover, which roams our neighbour planet Mars, has found active organic chemistry. This is big news because organic matter is one of the necessary conditions for life to emerge. Here’s what the team said about the discovery (emphasis mine):

We think life began on Earth around 3.8 billion years ago, and our result shows that places on Mars had the same conditions at that time – liquid water, a warm environment, and organic matter.

So if life emerged on Earth in these conditions, why not on Mars as well?

Curiosity confirms organics on Mars; Opportunity’s 10 year anniversary

This exciting piece of news makes us all wonder: what if, indeed, we found evidence that there is or there was at some point life on Mars? And what does that mean for us?

The Fermi Paradox

To better understand what that would mean for us, we’ll look at the Fermi Paradox. Let’s start with some maths:

There are around 1022 to 1024 stars in the observable universe. That’s 10,000 stars for every grain of sand on Earth. Our galaxy alone has between 100 to 400 billion stars. Knowing that around 5 to 20% of those stars are similar to our sun, then the lowest estimate points to at least 5 billion sun-like stars in our galaxy. Also, we know that those stars have a probability of around 22% of having en Earth-like planet orbiting it. Adding everything up, there’s at least 1 billion Earth-like planets orbiting sun-like stars in our galaxy alone.

Now we need to start getting speculative. How likely is it that a planet like that develops life? We know that Earth did, but we don’t know if this was a rare occurrence or not. So if we go for a conservative route and say there’s just a 1% probability of an Earth-like planet orbiting a sun-like star to develop life, then that means that there should be at least 10 million different planets with life.

Now, how many of those planets get life to evolve into an intelligent species? Once again, we know that life on Earth evolved to that point, but we have no way of knowing how rare we are. If we keep speculating with the same probability, then out of 1% of all those planets that developed life would emerge intelligent life. Adding all these conservative estimates up, that’s at least 100 thousand different intelligent species across the galaxy!

And that’s not all. The Earth is a young planet orbiting a young star. Our galaxy is old, and there are much older planets than ours out there. Can we imagine what would it be like for a species that evolved at the same rate as ours, but in a planet that’s just 1 billion years older? How would we be in a billion years from now? Colonising our galaxy? That’s estimated to take around 5 million years, so if we’re talking about a 1 billion year period, then that’s something relatively quick to do for such a civilisation. Sending communications to other places in the universe? Also pretty likely. So if there are younger intelligent species, they should be already at that stage. The universe should be full of interplanetary communications from many different civilisations, and our galaxy should have been colonised by now.

Where is everybody?

So if the universe should be so full of life and communications, how come haven’t we seen anything yet? Our observations never registered any kind of artificial device that wasn’t launched from Earth. And although we keep listening for signals in many different wavelengths from space, we still didn’t get a single message. This doesn’t make any sense, when we think of our previous estimations. So there must be something else going on.

Theory 1: They’re there, we just haven’t heard from them

One theory is that those civilisations exist, but for some reason we just never heard from them. And there are many possible explanations.

Maybe some colonising species did indeed visit Earth at some point, but since our civilisation and recorded history are so young, they could have visited well before that, and so we would have no way to know about it now.

Or maybe our galaxy is colonised, but we just live in some desolate rural area. Similarly, we could still be considered too primitive by more developed species, and so we could be living in some protected environment (think of something like a zoo).

One scary possibility is that there might be a highly developed predator species. This would explain not only a lower number of existing intelligent civilisations than what we estimated, but also why they could be hiding their presence instead of broadcasting it. Let’s not think too much about this one, OK?

Maybe our technology is just too primitive and our understanding of space too incomplete. We’re listening for radio signals, but maybe they use radio as much as we use smoke signals. Maybe there’s a lot of communication going on using different channels, like by manipulating sub-atomic particles, and we’re just too primitive to be able to listen to that.

Many other possibilities exist to try to justify this. Maybe colonisation doesn’t make sense for higher civilisations after all, or maybe we’re just a product of a simulation of some other species, or maybe it’s something else no one thought of yet.

However, there’s a scarier theory to explain this paradox.

Theory 2: There are no higher civilisations in existence

Maybe we’re really alone and there’s no one else in the entire universe. This should be highly unlikely, because of all the numbers we’ve seen before. So the best explanation for this is that we’re taking too much stuff for granted, and one of the steps between having a habitable planet and actually developing a galaxy-colonising civilisation must be nearly impossible to achieve.

This hypothetical nearly impossible step is commonly referred as the Great Filter: there are probably many planets creating the simplest forms of life out there, but at some point in the evolution process there’s this filter that eliminates almost all of them. These are some of the steps that might qualify as the Great Filter:

  1. Habitable star system
  2. Reproductive molecules
  3. Simple (prokaryotic) single-cell life
  4. Complex (archaeatic and eukaryotic) single-cell life
  5. Sexual reproduction
  6. Multi-cell life
  7. Tool-using animals with big brains
  8. Intelligent life
  9. Colonisation explosion

In this list, we’re currently on step 8, which means that we’ve successfully transitioned from all the previous steps. Unfortunately, because we don’t about any species from other planets, we don’t know how easy any of these steps are. Did we already pass the Great Filter and we’re now on our way to colonise the galaxy? Or is the Great Filter ahead of us?

There are many reasons to why the Great Filter could lie ahead of us: maybe a civilisation is unable to start harvesting its galaxy’s resources before running out of its own planet’s. Or maybe the development of advanced artificial intelligence can result in extinction due to unexpected consequences. Or getting to galaxy exploration may take too much time to avoid some life-ending asteroid collision. Among many other depressing possibilities.

Back to Mars, what can we learn?

Looking back at the list of possible steps for the Great Filter, what would it mean for us to find life on Mars?

Imagine that we find life on Mars at step 5: “sexual reproduction”. This means that that step and all the previous ones were easy steps, since 2 out of 2 studied planets (Earth and Mars) managed to get there. So the probability that the nearly impossible step lies ahead suddenly increases. In addition, still considering that example, we can assume that the next step, “multi-cell life”, would also be easy, since we’ve got records of that happening 46 times already. So the only possible difficult steps would be 7 (“tool-using animals with big brains”), 8 (“intelligent life”) or 9 (“colonisation explosion”). That would mean that the probability of having the Great Filter ahead of us would suddenly jump to 1 out of 3.

So, in conclusion, if we found life on Mars, we’d probably be doomed, because that would mean that the chances of having the Great Filter ahead of us would increase dramatically. And having the Great Filter ahead of us means that our chances of reaching the next evolutionary step are as good as none.

Some interesting reading material if you found this topic interesting: