The smallest self-sustaining ecosystem: Part I

Ecosystem in miniature: A mushroom grows among moss and decaying pine needles on the forest floor. (Lahemaa National Park, Estonia)

Life on Earth is complex and if we want to live out in space, it’s unlikely that we can take every species with us. Our ventures off-planet have carried only the bare necessities and due space constraints (pun intended), that’s unlikely to change in the near future. But constraints breed creativity, so to honor that spirit let’s look at what we small groups of species we can send off into space that would continue to survive without the umbilical cord of earthly supplies. Specifically, our question is:

“What is the smallest self-sustaining ecosystem that we could send to space?”

That’s a tough one, so we’ll start by defining what we mean in this question. First, let’s tackle the meaning of ‘ecosystem’. This is the word we use to encompass many different species living and interacting with each other and the nonliving components of their environment. This is the mix of all the microbes and trees and animals in a rainforest, combined with who eats who and conditions like the amount of rainfall or sunlight available. It is the tiger that eats the deer that eats the leaves, who dies to be eaten by the worms and microbes, who make the dirt to feed the leaves to feed the deer to feed the tiger. This isn’t merely poetic, it’s the literal passing of matter and energy, physical stuff and the power to move it, between individual parts that comprise the ecosystem.

Simple Ecosystem: dead plant matter (a log) feeds moss and fungi, which in turn feed a fly that will die to become food for more plants. (Bialowieza Forest, Poland)

Now, let’s move on to ‘self-sustaining’, the hardest part of our question. We want our ecosystem to continue without supplies from Earth. Is that even possible? Hypothetically yes, but it depends what you mean. Earth itself survives without supplies from elsewhere, passing matter between the living and nonliving in ecosystems – in this sense, Earth is a closed-loop system, moving physical stuff, matter around without gaining or losing matter from an outside supply*. But that’s just matter. Energy is a different story; the sun constantly supplies Earth with energy that flows through ecosystems and eventually dissipates back out to space, mostly as heat. So if we’re talking energy, Earth is an open-loop system, constantly being supplied more energy.

While it would be amazing to make an ecosystem that is both closed-loop for matter and energy, the problem with energy is that it decays into ‘useless’ energy like heat that cannot be used by life. Yes, I feel that irony writing from -10C temperatures in Boston, but it’s scientifically true. So for our question, we’ll aim to find an ecosystem that’s closed-loop for matter, but gets an energy supply from elsewhere. Even this is a hard problem; Earth is huge and while individual ecosystems are mostly ‘closed-loop’ for matter, they’ll shunt waste products off to other ecosystems to use. In space, we won’t have that luxury. Any waste made in an isolated, spacebound ecosystem must be used by something else in that same ecosystem.

Stuck in the bucket: matter usage in a spacebound ecosystem would have to be almost entirely, if not totally closed-loop. (Banks of the Danube in Budapest, Hungary)

And lastly, what do we mean by ‘simplest’? We could say that ‘simplest’ just refers to the fewest number of different species in our ecosystem. After all, fewer moving parts that can have something go wrong is better, right?  Or we could say that ‘simplest’ refers to how complex the species in our ecosystem are, meaning we’re looking to work with the simplest parts we can get. This would be microscopic life like bacteria, amoebas, fungal yeasts, cyanobacteria, and single-celled algae, which have the benefit of being small as well as ‘simple’.

Finally, we could take a step back and erase species from the equation and instead say the ‘simplest ecosystem’ is just the fewest number of chemical reactions to keep matter moving through the environment when you add energy. This is like cutting away all of the walls and membranes on cells and just looking at their metabolism, what chemical reactions they are running to convert starting reactant A into finished product B. Another reaction then need to take B and make C, and a third reaction then takes C and makes A. For now, we won’t settle on a specific definition of ‘simplest’, but will keep all of these in mind as we look for the simplest self-sustaining ecosystem.

A “simple” ecosystem with only a few visible species may have thousands more unseen microbes carrying out complex chemical reactions. (Bialowieza Forsest, Poland)

Speaking of, where are we going to look?

Good question! Stay tuned for Part II, in which we’ll speculate on where to start looking for  the simplest self-sustaining ecosystem.

The Plan


The best friends in life are those that challenge you to be more than you are already. This is the first post on this blog, answering a challenge from two of my closest friends to lay out plans for a future not yet possible: long-term space travel to other worlds and planetary systems. For this future, we’ll need not only dramatic advances in not only mechanical and energy technologies, but also biological technologies that will support our survival in space. As someone with a PhD from synthetic biology, where we are beginning to engineer life as we can imagine it, I’m going to build a company that will create these technologies. 

This blog is part of that: I will using it to discuss biological research breakthroughs and how they can be applied to help humanity achieve long-term space travel. Below is the rest, a 10-year plan for the future. 

My ten year plan to move from PhD in biology to CEO of a biotechnology company enabling space travel breaks down into three parts: developing business understanding, building startup-related expertise and connections, and identifying problems in space travel that can be addressed with biotechnology. Starting in 2018, I will develop business understanding through my consulting work at ClearView Healthcare Partners. I will focus on working with startup clients for medical and microbiome applications, building my connections and expertise in running a startup. After I settle into my consulting role, I will start research projects in a local DIY bio laboratory to maintain a hand in research connect with talented new researchers.

In 2020, with a perfected view of what we need to make living in space a reality, I will harness my expertise and connections to launch TerraForma, a company that creates biotechnologies for space travel. TerraForma will initiate with two branches of projects: “sure bet” projects with a high likelihood of success and applications to non-space travel (e.g., medical supply and storage), and “big play” projects that are riskier but solve problems essential for surviving in space (e.g., fuel and materials production, self-recycling miniature ecosystems). We will begin with one project in each branch, and expand our project number as our research capacity and funding grows. Revenue will initially come from grants and angel investors, and will switch to licensing for developed technologies and patented innovations within 5 years.

By 2022, the year Elon Musk plans to send humans to Mars, we will have our first commercial technology from a “sure bet” project completed and fully tested on the International Space Station or a private spacecraft. By 2025, TerraForma will bring its first “big play” project to fruition, creating a microbial community capable of either sustained resource production from minimal inputs or a self-sustaining microbial ecosystem that can support animal life. And in 2027, the first of our ‘big play’ projects will be available in spacecraft as a primary support system for human life in space. Past the first 10 years, TerraForma will work to create several self-sustaining biological systems onboard spacecraft, with the ultimate goal of enabling indefinite space travel and making us an intergalactic species.

This blog will stay quiet for a while, as I finish the last six months of a yearlong trip to circumnavigate the globe. That journey is being detailed here

Biological stars: glow-worms in New Zealand