It is a refreshing fact that the prospects for human survival are substantially higher if we live on two worlds, instead of just Earth. The moon, say, or Mars… every extraterrestrial body poses unique technical challenges to colonization. Yet nearly all are at least potentially habitable – in theory. Our survival prospects climb higher for three worlds, higher still for four. The more worlds we colonize, the more likely a colony on at least one of them will still exist at any given future moment. It’s like flipping quarters: the more you flip, the greater the chance at least one will come up heads.
Last time: More Exotic Colonization Options. This time: Pluto and Eris — the Outer Limits
The outer limits: Pluto and Eris. Pluto just does not get enough respect. Last hired and first fired of the planets, it was discovered on Tuesday, February 18, 1930, in Flagstaff, Arizona by self-made astronomer Clyde Tombaugh. It was forced into retirement by an act of the International Astronomical Union, which revoked its full planetary status on August 24, 2006, after only 76 years on the job. Pluto has been technically renamed “134340 Pluto” and relegated to dwarf planet status, to the continued consternation of Plutophiles everywhere. To make things worse, it is not even the biggest dwarf planet, or for that matter the most distant. Those honors go to Eris, discovered in 2005 and not that well-respected either (many people have never even heard of it). As targets for colonization these bodies have problems, though nothing like those associated with the gas giant planets or even Venus. The main problems are getting there in reasonable time, and obtaining enough light energy to warm the colony (which is sealed to keep the air in), to grow food, and to generate electricity such as with solar cells.
A one-way trip to Pluto is feasible in about 9 years. The New Horizons spacecraft launch of January 19, 2006, destination Pluto, was designed with a planned travel time of 9 years and 176 days. Eris is less than four times as far away as Pluto. Sometimes it can actually be closer to the sun than Pluto, though this won’t happen next for about 800 years.
Prospective colonists will have severe energy challenges once they manage to actually get there. Pluto’s distance from the sun ranges from 29.7 times Earth’s average distance, up to 49.3 times Earth, depending on where it is in it’s rather uncircular orbit. For Eris, the range is from 37.8 to 97.6 times Earth. Unfortunately the brightness of the sun is related to the square of the distance, not the distance itself, so the sun on Pluto is actually between 880 and 2,431 times weaker than on Earth (i.e., 29.7×29.7 to 49.3×49.3).
With the sun so weak, sunburn would be the least of your worries. In essence, you’d need 2,431 computer-controlled mirrors all reflecting the sun to the same spot, to be sure to get up to at least Earth’s sunlight intensity at that spot. Then, if that spot was inside an transparent, airtight bubble, you could grow crops there, right at that spot. If you wanted to grow 1 acre of crops, on the order of what’s needed to support a person, you’d need up to 2,431 acres of computer-controlled mirrors. During favorable periods you’d need less, as “few” as 880 acres, but you do have to eat during the unfavorable times too. For Eris, the sunlight is as low as 9,518 times weaker than Earth (implying 9,518 mirrors for Earth-style light intensity). Though this sounds dim, it is actually about 35 times brighter than the full moon, so you could see well enough to get around without artificial light or mirrors. Still, mirror manufacturing definitely needs to get more cost-effective before colonization becomes feasible, unless some other energy source can be found besides the distant sun. Once the energy problem is solved — well, bon voyage!
What we can do now
Tracking the advance of space technology. It would be good to understand how quickly space-faring technology is advancing. Research on elaborating, testing, standardizing and using such technology tracking methodologies should be supported by academic research, incentivized by government research funding. That way we would know better what to get ready for in terms of a time frame for future space colonization. The leading approach could be expanded upon. It is termed “Technology Readiness Levels,” or TRLs, and is used in the US by the National Astronautics and Space Administration (NASA) and the Department of Defense (DoD) as well as other organizations worldwide. TRLs classify relevant technologies on a spectrum, such as from speculative on to mature. “Speculative” describes, for example, proposals for faster-than-light travel via cosmic wormholes. “Mature,” on the other hand, could be applied to space systems that reach operational status, like the US space shuttles of the early 21st century.
From sunbathing to moonbathing to starbathing. Closer to home, it is useful to keep in mind that moonlight is hundreds of thousands of times dimmer than sunlight. This means that, though sunbathing is hazardous even with sunscreen (as we will see later), moonbathing is perfectly harmless, and perhaps even fun. Feel free to go right ahead. But don’t expect to get a moontan as the light is simply too muted and pale, even compared to sunshine on Pluto or Eris. So that’s the situation with moonlight…but what about starlight?
The brightest star in the heavens is Sirius, with an apparent magnitude of –1.47. This is quite a bit dimmer even than the full moon, whose apparent magnitude is about –12.9. The lower the apparent magnitude, the brighter the object. The sun, for example, has an apparent magnitude of –26.7. We can explore this issue further, in case you run into someone inclined to concentrate starlight from Sirius to sunlight-equivalent intensity for the exotic purpose of tanning by starbathing. A difference in apparent magnitude of 5 is defined as a 100-fold change in brightness. The difference in apparent magnitude between the sun and Sirius is a little over 25. At a factor of 100 change in brightness for every 5 levels of magnitude, 25 levels means a hundred-fold brightness change compounded 5 times, for a total change in brightness of 100×100×100×100×100, or 10 billion. In other words, starlight from Sirius would need to be concentrated more than 10 billion times to reach the intensity of sunlight. At roughly 4 billion square inches in a square mile, that means about 3 square miles of starlight from Sirius focused onto a single square inch. Since starbathing requires more than a square inch of light, that pretty much means an entire metropolitan area or its equivalent devoted to focusing Sirian starlight onto your beach towel. Other stars are dimmer and would require even more area.
From starbathing back to sunbathing. However impractical, starbathing at sunlight-equivalent intensity is possible in principle! However, it would be unhealthy, and for the same reason that sunbathing is unhealthy. Sirius is much hotter than the sun so its light is more skewed toward the ultraviolet. Thus protecting the skin from UV (ultraviolet) exposure from super-concentrated starlight would be very important. Sunscreens are typically rated in terms of ability to filter out B (medium wave) type UV (abbreviated UVB), which causes sunburn. They tend to let through A (long wave) type UV. This UVA does not cause sunburn, but does damage the skin, causing the most dangerous kind of skin cancer, malignant melanoma. This is consistent with the lack of evidence that ordinary sunscreen use protects against this often-deadly cancer. Even ordinary window glass does not screen out UVA reliably. In short, star-tanning, like suntanning, should be avoided. On the other hand, appropriate sun exposure is needed to create vitamin D in the skin. And ordinary starlight is so attenuated that starbathing at night under unconcentrated starlight is perfectly fine if you feel like doing it, just like moonbathing. Enjoy!
Communing with your inner colonist. Take up vegetable gardening, just like space colonists likely will! Food production in extraterrestrial colonies might involve hydroponic tanks or chemical factories producing soylents of various colors for food. But production may also involve growing plants, just like on Earth. Off-Earth farming will resemble vegetable gardening more than commercial agriculture. Instead of acre after acre of a single crop, colonists will grow many different kinds of plants in modest quantities inside the colony’s bubble. That will give the colonies more diverse and thus robust ecosystems. It will also make for a more varied diet for the colonists, which is healthier as well as better-tasting. So, while growing your own vegetable garden, you can work knowing that you are doing what the space colonists of the future will likely do. Your gardening experiences here on Earth, both good and bad, will mirror to a significant degree those of future space colonists and deepen your understanding of space colony life.