Thomas M. Kehrenberg

Extraordinary things on Mars

This article was inspired by some objections to Elon Musk’s plan to put 1 million people on Mars before the end of the century. I am not concerned here about practical or financial objections to the plan but the objection that a human colony would harm Martian life.

The hypothesis of life on Mars has a long history. Already in the 19th century people entertained the thought of contact with Martians. Around 1900, Percival Lowell became famous by speculating about a civilization on Mars after the astronomer Giovanni Schiaparelli had found canals there with his telescope. The sighted structures turned out to be an optical illusion but the lure of alien life remained.

Traditionally, Martians are represented as small green humans with weird ears, but with legs, some sort of feet, arms, some sort of hands, a head and some sort of eyes. It is of course extremely unlikely that a species that evolved separate from us looks so similar. The NASA scientist who look for life on Mars presumably don’t expect to find these kinds of Martians with their probes. What they don’t rule out are some simpler life forms. Mars landers typically look for organic molecules and water that could be a clue for Martian life.

The possibility of life makes Mars very interesting. Since the end of the cold war there have been 7 missions to Mars which is only topped by 9 missions to the Moon (Missions to other celestial bodies: 1 to Mercury, 2 to Jupiter, 1 to Titan, 2 to Asteroids and 2 to Comets).

So, why do we care so much about the possibility of life on Mars? There are multiple reasons. One is academic interest. Scientists simply like to know stuff. And if we found life on Mars, it would help a lot in answering the question of how life originated on Earth. This is a valid reason and pretty uncontroversial.

Another minor reason is the fear of Martians attacking us. In order for them to be a significant threat they would need to be able to affect other planets. As we haven’t found any artificial structures on Mars, any potential civilization is either living underground and unlikely to have invented rockets or is so advanced that it could have killed us ages ago but didn’t. In general, it is unlikely that an alien species is ever roughly at the same technological level as we are. We aren’t even at the same technological level as humans 100 years ago. And 100 years is a rounding error on the relevant time scales (our species has existed for at least 200,000 years already). So either way, there is not much use in worrying about attacks from Mars.

Now, since human colonization of Mars became a serious possibility there is a third reason why native life there is relevant: ethical concerns. The concern that we somehow harm Martian life. For example by introducing terrestrial bacteria which then reproduce until they have taken over and driven Martian life to extinction.

I have a couple of objections to this concern. My objection is not that terrestrial life has the birth right to destroy everything that gets in its way. Rather I will argue that either Martian life is so alien that terrestrial life poses no threat or there is no life on Mars.

To begin, let us ask where these ethical concerns come from. What is it about Martian life that we value? My answer is that we care about it because it has the potential to be interesting. (If we found conscious beings on Mars they would be eligible for additional consideration beyond their being interesting to look at, but I consider that possibility extremely unlikely.) As humans we value diversity. If every animal on Earth looked the same, that would be very boring. That’s why we protect endangered species. Life on Mars is potentially much more interesting that terrestrial life because it might not be based on DNA and we could marvel at the possibilities that our universe permits.

Before we go into the details I want to broaden the scope of the consideration a bit. “Life” is notoriously hard to define anyway so let’s talk about instead about a class of phenomena that definitely includes life. Let’s talk about extraordinary things. Our sun is not extraordinary, there are at least a few billion stars like it just in our galaxy. As we now know, Earth-like planets are also pretty common and therefore not extraordinary. I propose the following definition of extraordinary things: things that were produced by optimization processes.

An optimization process that we are very familiar with is evolution. Evolution is based on replication with small errors combined with natural selection over many, many iterations. The chances of a living fox spontaneously forming in a primordial pool are basically zero. What makes the fox extraordinary is not just its rarity but also the fact that it seems to serve a function, that it consists of many different parts that work together. Without the first replicator there would have never formed anything like it (except Boltzmann foxes of course). The first replicator and the subsequent optimization process made it possible.

The chances of a fox spontaneously forming on Earth out of nothing is negligible but evolution can pull it off! Evolution can step-by-step discover things that work which it then keeps and discard all the other ideas that don’t work.

Other optimization processes don’t have to look like evolution. However, evolution is always an obvious candidate because it requires relatively little to get started. I haven’t heard anyone proposing an even easier to start process but of course that doesn’t mean it doesn’t exist.

Now, the possibilities for extraordinary things on Mars are literally endless so I would like to distinguish two cases: things that are roughly similar to terrestrial life (call this category 1) and things that are incredibly alien (category 2). I will apply the term ‘similar’ very broadly.

Basically, category 1 things are things we should notice. Bacteria are category 1, von Neumann probes are category 1. I’m not really sure what the necessary properties of category 1 are; but here is my attempt:

  1. made out of atoms
  2. reproduces in some manner

Property 1 is necessary so we can notice one another at all. Maybe this constraint can be relaxed a bit but I don’t see an obvious way how.
Atoms seem to be the most stable building blocks in our universe.
Concerning property 2, if something does not reproduce it is unlikely that we ever meet it because there are presumably very few of it. The universe is large and our lives short.

Category 2 is everything else. Things we probably won’t notice. They could be on Mars right now and we would have no idea. Maybe if we lived there we would notice strange patterns in the wind or something.
Communication would be basically impossible. Still, we don’t want to harm those non-corporeal Martians, right? Well, here is the thing: if it exists on Mars, it probably exists on many other planets as well. It would be way too much coincidence if right next to Earth would be the only planet with these cat2 things. Remember, we can’t see them.
They’re probably on Venus as well. Maybe even on Earth. In that case it’s really terrestrial life that needs protection. Terrestrial life is the one that is threatened by extinction, not cat2 things.

This rests on the argument that if cat2 things exist, they’re everywhere. This argument is borrowed from the Fermi Paradox. The Fermi Paradox asks, “where are all the aliens?” It is concerned with cat1 beings, i.e. beings we can notice.

There are a lot of good discussions of the Fermi Paradox with possible explanations, so I won’t reproduce them here. The summary is: considering that life happened at least once, and there are 20 billion planets in our galaxy and the universe is 13 billion years old, there should have been some species before us. And some of those should have become intelligent and built machines that replicate. At 1% of the speed of light, a probe only needs 10 million years to traverse our galaxy. A civilization with a head start of 1 billion years could have easily colonized all planets in the milky way by now.

However, we haven’t found any signs of aliens.

This gives something of an upper bound for the frequency at which cat1 things arise. If life happened on every planet, we surely would see aliens. Similarly if it happened on every 10th planet.

For the Fermi Paradox to make any sense, cat1 things have to be quite rare. So, there probably are no cat1 things on Mars. (Except for the case where life originated on either Mars or Earth and spread to the other, but in this case Martian life is just terrestrial life and it loses a lot of its specialness.)

As an aside, the general fact that there is life on Earth is not a very good indicator for the probability of life on other planets, because considering that we are here to ask this question, life on Earth is a given. Life only has to happen once for us to exist. This is related to the anthropic principle.

For cat2 things there is no Fermi Paradox because as far as we know the galaxy is full of cat2 things. There are a lot of planets like Mars. And some that are a lot older than Mars.


Further notes:

Proposed new structure (rewrite the whole thing):

  1. explain Fermi paradox (we don’t expect alien ships to land here, we expect gray goo)
  2. propose solution to Fermi paradox (abiogenesis is hard)
  3. discuss other solutions (great filter)
  4. answer the question: but if abiogenesis is so rare, how come we are here?
  5. introduce anthropic reasoning

stars. But a successful replicator does spawn other successful replicators that can improve upon their already successful ancestor.
That is why life is seemingly improving and stars are not.

The chances of a brain spontaneously forming out of nothing is negligible but evolution can pull it off! Evolution can step by step discover things that work which it then keeps and discards all the other ideas that don’t work.

As an analogy consider sorting an array of integers. The way it works without evolution (or any other kind of optimization process), is that you shuffle the array at random until the numbers are in the right order. This strategy will work okay with smaller arrays. If there are 10 elements, there are about 3 million possible orderings. But assume we want to built a cat. There are about 10²⁷ atoms in a cat and they all have to be roughly at the correct position; otherwise the cat won’t work. Even if we say we only need to get 10²⁰ positions right, the number of possible orderings is still gigantic. It is a number with 10²¹ zeros. (So, not 10²¹ but 10^(10²¹).) As a comparison, in units of Planck time (10⁻⁴⁴s), the universe is only about 10⁶² units old. If you tried one cat design per Planck time since the beginning of time, you still wouldn’t have any chance of discovering a working version any time soon.

In the integer array example, evolution could be likened to bubble sort. It doesn’t have optimal time complexity (merge sort is even faster) but bubble sort gets the job done much faster than simply trying out every possibility.

The first ever brain structures appeared in worms over 500 million years ago. Accordingly it took evolution about 3.5 billion years to come up with brains. A modern genetic algorithm on a computer cluster could have come up with worm brains in maybe a hundred years (this is a wild guess of mine), so evolution is not especially fast, but it does eventually get there.

What this illustrates is that optimization processes are pretty powerful. It’s the reason why brains can be so complicated while the rest of the universe is pretty uniform. You can describe the structure of the sun in one book and with a few formulas. But we’re nowhere near understanding the human brain.

This leads us to the second point of this article. For there to be extraordinary things on Mars there had to be an optimization process to produce them. In a sense, the existence of a watch depends on the existence of a watch maker.

Now, the optimization process doesn’t have to look like the process that generated us. But it is required that the process is able to accumulate improvements. Evolution wouldn’t work if children had nothing in common with their parents. Humans are able to built airplanes only because Newton developed mechanics and all the scientists after him improved upon it.

That leaves us with the difficult task of estimating the chances of such an optimization process occurring on Mars and it running long enough to produce non-trivial results. As in estimating the probability of an Earth-like replicator appearing on other planets, the only things to guide us are our understanding of the laws of nature and the Fermi paradox.

I see basically only two possibilities:

  1. There is a form of weird alien life that we aren’t able to detect and the galaxy is full of it.

  2. Life in any form is so rare, that there are at most a handful of planets in the galaxy that have it (Mars not being one of them).

This rests on the following hypothesis: if it happens on Earth and on Mars, it happens everywhere.

You’d have to have a good reason for claiming simultaneously that evolution-like processes are rare and that they happened on two neighboring planets. Sure, I can think of reasons (like exchange of DNA through a series of unlikely asteroid impacts), but they would all imply that terrestrial and Martian life are extremely similar. So it wouldn’t really count.

In case possibility 2 is true, I see no valid objections for colonizing Mars. On the contrary, as Earth-like life is so rare, we should spread it. Plant a few flowers on Mars, for example.

In case of possibility 1, I would still be in favor of colonizing Mars.

I’ll end this article with a scandalous appeal to emotion: Watch this and tell me you don’t want to visit those places. (Humans can fly on Titan by muscle power!)