Planet B: the math of a new home in space

topMichel Mayor was one of two scientists awarded the Nobel prize in physics for finding the first earth-like planet outside of our solar system. This is one of the more exciting parts of discovering thousands of new planets, including the seven-planet Trappist system, forty light years away, diagrammed above. He gave an interview which has been widely distributed in which he said we will not colonize another planet as a way to deal with Earth becoming uninhabitable. The reason to write a blog about it is that what he is saying is both critically important and almost certainly wrong. The problem, as it often is, is a lack of nuance that can be restored by looking at the basic math. In this case the key phrase is “we will colonize” — the idea is problematic.

We begin with an analogy to European colonization.


It would be very difficult not to believe that Europeans colonized the Americas. They are all over the place, almost everyone in the Americas speaks a European language, and there are organizations fighting to preserve what little remains of the aboriginal peoples, cultures, and languages. Colonization off Earth will at least have the signal advantage that it will avoid horrible mistreatment of aboriginal peoples.

Many of the people who came from Europe left to avoid war, famine, religious persecution, and poverty. Given the technological differences, we are facing a similar situation. Earth is getting less comfortable, it may get a lot less comfortable, and leaving for somewhere else may be an option. Yet a Nobel Prize winner in a field completely unrelated to colonization says we will not do it.

While I do not presume to put words in Dr. Mayor’s mouth, my best guess is that he is correctly making the assertion that, if we do not take care of Earth much more effectively than we are now, billions of people will die and we will absolutely not be able to rescue them by moving them to another planet. That has little or nothing to do with the chance we will colonize another planet. The fraction of the people that moved from Europe to America was tiny — almost everyone stayed behind. The European swarms in present-day America were born here. A few colonists can generate a lot of people, because populations expand exponentially until they hit resource limits.

Usually, there are survivors.


The scenario that everyone will die because we are wrecking the Earth is pretty much nonsense, but the scenario where almost everyone dies and the survivors end up in domed cities that need machinery just to keep the air breathable — that one is plausible to Occupy Math. Likewise, it seems very likely that we will colonize at least the Moon and Mars, living in domed cities or underground colonies. We have already found the resources in both places to make a colony work. The trick is that the number of people transported will be in the low hundreds in the first century and, even after a thousand years, will be a drop in the bucket compared to the population of Earth. We will colonize and we will not take everyone along.

Human beings are all about what they are used to. Living on planets may be highly overrated. The picture above is the inside of a 20 kilometer long rotating cylinder in a stable Lagrangian orbit in the Earth-moon system. A space colony can be constructed from lunar materials. It spins to prevent health problems due to low gravity. It is ideally positioned to collect vast amounts of solar power. It is already in orbit so there is no cost of fighting your way up from the surface of the earth if you want to travel. The surface of the moon has enough materials to make hundreds of thousands of such colonies that each house hundreds of thousands of people. Using space colonies makes the number of people rescued pretty large — maybe as high as one in a thousand. Still not an argument for not taking care of Earth.

We are not colonizing an extra solar planet anytime soon!


Dr. Mayor won his Nobel prize for finding an earth-like planet outside our solar system. Conservatively there are a billion such planets in our galaxy. All of them are too far away to take anyone to them. Take the Trappist system — at forty light years away, it is a system right in our galactic backyard. Forty light years is about 37,800,000,000,000,000 kilometers. It would take centuries for the best unmanned probe we have to get there. This is just not practical right now and will not be practical for some time to come. Worse, “earth like” currently means “about the right size and distance from its sun”. A horrible example is the planet Venus. Venus is an earth-like planet by this definition. It may even have been a habitable planet 3 billion years ago, something that makes Occupy Math really nervous with respect to our current green house problems.

To colonize an extra solar planet, we either need new physics or a huge amount of time. Let’s look at the options.

  • We build a ship that can make the trip in several centuries maintaining an earth like eco-system in its interior. The ship is probably fusion powered and is called a generation ship. This notion requires a huge breakthrough in fusion power and in balancing an ecology, something we have failed to do multiple times in sealed environments.
  • Send a fast unmanned probe with the information needed to build humans at the far end and to raise them. This is science fiction, but it may someday be possible. This involves no one at all from Earth being in the proposed colony.
  • Discover new physics that permits faster than light travel so we can get somewhere in less than centuries. This is science fiction and we only have a sniff that it may be possible. In any case, faster than light ships will be like European colonization all over again — almost everyone must stay home.


Definitely preserve Earth!

Dr. Mayor’s central point — that colonization is utterly not an alternative to taking care of the planet we live on now — is one with which Occupy Math agrees without qualification. There is an unfortunate tendency in the ecological community to view off-planet colonies as a dangerous distraction from working to preserve the earth. This is almost certainly arrant nonsense. Resources from space, especially cheap solar energy and safe places outside the biosphere to conduct research, are potentially key tools in preserving the current ecosphere. Off-planet colonies are also a way of hedging our bets.

A good example of this is Neil deGrasse Tyson’s statement that “If we have the technology to terraform another planet, we have the technology to save this one.” This statement assumes that these goals are in conflict when they are actually synergistic. Terraforming Mars, for example, would teach us many things about geoengineering that would be extremely dangerous to experiment with on Earth. Beyond that, Earth has a huge number of people on it that need a continuously intact ecosystem and whose permission is ethically required before we take steps to save them. It seems likely that terraforming Mars is actually much easier than fixing Earth and potentially a critical lab for figuring out how to fix Earth.


Since this is Occupy Math, let’s conclude with a nod to the math. Most of the excitement over potential extra-planetary colonies suffers from a lack of understanding of the scale. Space is deep, interstellar space is intractably deep, and most plans that look possible would take centuries to bring to fruition. Estimation of and understanding of scale are basic mathematical skills and extra-planetary colonization is a wonderful place to explore these issues. Any thoughts? Please make an appearance in the comments.

I hope to see you here again,
Daniel Ashlock,
University of Guelph,
Department of Mathematics and Statistics

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