NASA are idiots. They want to send canned primates to Mars!

—Charles Stross, Accelerando

The universe offers many more ways to die than to survive. Surprise! Possibly the only place in the entire universe for us humans is right here on good old terra firma. Even on our home planet, we can't survive just anywhere. A lot of the land is frozen tundra or arid desert—and don't forget that most of the area is covered by oceans.

I wouldn't want to see the scary ending of the “all eggs in one basket” scenario. What if an asteroid struck the earth, or global climate changes caused human extinction (unless we embrace transhumanism), or, if you want to go all science fiction, alien invasion? So, if not solely for the pure joy of exploration, some of us should probably hightail it off the earth and start filling other baskets.

To me, the most interesting alternative to being cramped inside enclosed space station habitats or hollowed-out asteroids is to colonize another planet. Only, as with most things in survival science, this idea isn't quite that simple to realize. What are the odds of landing on some planet that offers the bare necessities and biodiversity essential for human life? Probably less than getting two royal flushes in a row.

I've heard that, on rare occasions, cheating arises in poker. An unscrupulous dealer might manipulate the cards to help one player. Since it is unlikely for humans to move to a ready-made planet, scientists have been thinking up ways of doing a bit of cheating to improve the odds. They have thought up ways to rig our bodies through genetic modification or to rig the planet's environment. This chapter focuses more on the planetary science, but I'm sure genetic manipulation will pop in from time to time. Colonization will probably require a blend of both.

The climate science of the last chapter is important not only for understanding the earth but for understanding how to adjust the environments of other planets. As a science Zen master might say, “Before we can change another world, we must understand our own.” This outward-looking planetary science is called terraforming, the science of making other planets (or asteroids) more hospitable to Earth life.

Terraforming is all about tweaking what a planet already has. The amount of tweaking depends on how different the biosphere of the target planet is from Earth's and/or on how much we have modified our bodies. In the end, terraforming might be our escape hatch if something disastrous happens to our planet.

Fig. 12.1. Illustration of terraforming.

Terraforming was first mentioned not in a scientific journal but…in science fiction. The word was first used in the short story “Collision Orbit” by Jack Williamson in 1942.1 It took a while for mainstream science to get the jargon right. Does the original scientific term ecosynthesis sound as exciting? I thought not.

WHAT BASIC PLANETARY ELEMENTS MAKE FOR HAPPY COLONISTS?

1.They want what one of the Three Bears had

The most ready-made planets for colonization are probably located in the circumstellar habitable zone of a solar system. Thanks to the popular press, you've probably heard this being called the Goldilocks zone, where a planet will be not too far from or too close to a star for our type of life. The greatest chance of a planet having sufficient atmospheric pressure to support liquid water on the surface lies within this zone.

Outside the Goldilocks zone, water can exist, but it would probably have to exist below the surface of a planet or moon. It wouldn't be easily accessible. The zone's size varies between solar systems depending on a star's luminosity and age. And within a solar system, the zone doesn't remain constant. As our sun ages, it will bloat outward, pushing its own Goldilocks zone outward.

2.Flicking on the lights

To make the planet conducive to life as we know it, specifically human type, there has to be enough light for photosynthesis. Plants need that energy to produce oxygen, and oxygen tends to be a good thing for colonists. To terraform a planet outside the Goldilocks zone, giant mirrors might be used to focus sunlight onto a planet. A higher-level civilization, maybe a type II, might consider dragging a planet closer to a sun. For now, this is pure science fiction.

3.The need for gravity

The mass of the target planet is important. Remember that general relativity states that the more massive the planet, the greater the gravity. Colonists will be concerned about gravity for at least two reasons. First, the planet needs enough gravity to maintain an atmosphere. Second, it directly affects the quality of human life.

The effects of microgravity (when an object appears to be weightless as in a freefall) include loss in bone density, brain damage, eye damage, and heart damage. Don't forget that your digestive system needs at least some gravity to help push down food and waste. Our bodies evolved in an environment of 9.8 meters/second² (32 feet/sec²) of pressure. How low can gravity go before health is adversely affected? Scientists aren't sure.

On the flip side, scientists also aren't sure of the long-term effects of excess gravity. So, depending on the planet of choice, we must either alter the gravity to make it habitable or (again) alter our bodies to survive.

4.Take it out for a spin

The speed of planetary rotation matters. Too long or too short of a day can be challenging to baseline human life. We evolved on a planet with a twenty-four-hour day, so extreme day and night cycles might not be advantageous to our plant or animal life.

A couple of solutions are possible. We could use solar shades to manipulate a planet's day and night cycle. If you happen to come from a type I or II civilization, you might decide to change the rotational speed of a planet by crashing asteroids against it, thereby causing drag against its gravitational field to slow it down. Naturally, this is before settlement.

5.Magnetism

Our planet has generously constructed a magnetic field (called a magnetosphere) around itself to protect us from solar winds. Solar wind is a stream of charged particles blowing out from the sun at a rate of five hundred miles per second.2 When solar winds strike the earth's magnetic field, the field stretches as it repels the winds and keeps our atmosphere intact. Finding a planet with one already constructed would be nice.

Fig. 12.2. Illustration of the magnetosphere. (iStock Photo/aaronrutten.)

Could one be added? In theory, yes. In terms of energy cost, it might not be worthwhile. A planet's core could be liquefied (like the earth's molten iron core) to create a planetary dynamo. The outer layer would rotate at a faster rate than its liquid center. How would you liquefy a planetary core? Many (many) nuclear bombs set to detonate around the core.

6.Tectonic plates

Colonists wouldn't want volcanic eruptions spouting out CO₂ at random times. Not to point any fingers, but if I did, my index finger would be aimed at Venus.

Tectonic plates are rigid plates in the planet's uppermost mantel. Subduction is the process where one plate is shoved beneath another. Subduction helps regulate Earth's natural CO₂ levels.

EXTRA RESOURCES: CAN ASTEROIDS BE USED TO OUR ADVANTAGE?

Quick fact: An asteroid is a large, rocky body in orbit around the sun. A meteoroid is a chunk of an asteroid, and a meteor is a meteoroid burning up in the atmosphere. A meteorite is what survives the passage through the atmosphere and whacks into the earth's surface.

It probably isn't a good idea to haul the earth's natural resources to the target planet. A better way to deliver raw materials is to mine asteroids. This idea first pops up in science fiction when we learn of Martians mining asteroids for gold in Garret P. Serviss's 1898 novel Edison's Conquest of Mars. I'm thinking that if exploiting asteroid resources was good for the fictional Martians, then it could be good (and possible) for us real earthlings. To keep the expense down, a multistep process called optical-mining would have to be used.

Step one is to design a vehicle that captures an asteroid in an inflatable bag. The spacecraft would have to be outfitted with reflectors that concentrate sunlight onto the asteroid. The heat would release water and other volatiles, chemical substances such as nitrogen or carbon dioxide. The best part is that the sun would be doing the mining, and for free!

Because mechanical drilling isn't required, maintenance would be cheap. Another benefit is that tons of water (a volatile) could be harvested and stored as ice. The water would be available for rocket propellant, used to produce oxygen, or even as drinking water for travelers.

Also, don't forget that hurling asteroids at a planet is not always a bad thing. Above, I mentioned that asteroid strikes can slow the rotational speed of a planet to make our day lengths more pleasant. As you will see below, asteroid impact can be used as a delivery system for volatiles.

THINKING GALACTICALLY BUT SEARCHING LOCALLY FOR A VACATION HOME

A snippet from Futurama:

Fry: I'm impressed. In my time we had no idea Mars had a university.

Professor Farnsworth: That's because then Mars was an uninhabitable wasteland, much like Utah. But unlike Utah, Mars was eventually made livable when the university was founded in 2636.

Leela: They planted traditional college foliage. Ivy…trees…hemp…soon the whole planet was terraformed!3

I suspect that this is not how Mars will be terraformed. The science sounds a bit shaky. I'm sure any colonist would be happy to locate a planet with the environment of Utah. Anyway, Venus and Mars make for some juicy local choices. As with most things, these choices come with their own unique set problems, but none are scientifically unsolvable. Although it might take a higher-level civilization.

The award for best size and location for habitation goes to Venus. It has 82 percent of Earth's mass and 95 percent of Earth's diameter, so gravity wouldn't be much of a problem at 91 percent of what you feel here. At its closest, Venus is only a half-shell away at a scant forty million kilometers (about twenty-five million miles).⁴ Not too shabby, but I haven't told you the problems or, rather, the single big problem. The runaway greenhouse effect gasses make the atmosphere over ninety times thicker than Earth's, making it the hottest planet in our solar system. Did I mention it is also toxic?

All this means is that we have a fixer-upper. Ideas for terraforming range from seeding the atmosphere with hydrogen, to produce water that will rain down and create surface oceans, to mining magnesium and calcium on the planet for chemical carbon sequestration. As they have with the earth, geoengineers suggest putting up solar reflectors between Venus and the sun to cool the planet.⁵ The panels would also help deflect the sun's solar winds, protecting the planet from radiation.

Venus has no magnetosphere, so it would be vulnerable to the solar winds without its thick atmosphere. As an alternative, it might be possible to place reflective balloons in the upper atmosphere. Why not have humans live in floating reflective cities while further terraforming is done?

If you asked the fictional Mark Watney from Andy Weir's The Martian, I'm sure he'd tell you that Mars is a solid possibility for settlers. Only make sure you don't go it alone. Mars is farther away than Venus, so the costs and risks involved of getting there are greater. At its closest orbital point, it is about fifty-six million kilometers away (about thirty-five million miles).6

Distance aside, Mars has a similar enough orbit compared to the earth's. Its day is only about forty minutes longer than ours. The planet contains both water and carbon. Mars is 53 percent the size of the earth, so visitors are stuck with only 38 percent of the earth's gravity. The lower gravity makes it hard to maintain an atmosphere. No magnetic field exists to protect colonists from solar radiation.

Back in the day (billions of years ago), Mars had a much more substantial atmosphere. Since then, most of it has leaked out into space. Thank the sun's solar winds. Because Mars is not protected by a magnetic field, solar winds blow off the planet's gas molecules at a rate of about one hundred grams of atmosphere every second.⁷ When the sun is in a particularly foul mood, it bombards poor little Mars with solar flares, increasing the loss by a factor of ten.

Not having a magnetic field is a problem but not a scientifically insurmountable one. It might all come down to transhuman genetics or liquefying the planet's core. An alternate idea was proposed at the Planetary Science Vision 2050 Workshop hosted by NASA in February 2017. NASA discussed how positioning a magnetic shield at a specific location could create an artificial magnetosphere to wrap around Mars and protect the planet.⁸

Another headache is temperature. While Venus is too hot, Mars is too cold. Don't worry, an aspirin will help. Take (at least) two of the following ideas on warming and call me in the morning.

Carl Sagan thought it possible to transport dark materials that would reduce albedo to the planet's polar ice caps. There they would absorb more heat and melt the ice. NASA suggested introducing greenhouse gasses to create an oxygen- and ozone-rich atmosphere.⁹ Volatile-rich asteroids could be aimed at the planet's surface where the volatiles would bolster atmospheric pressure. We could also try a reverse-Venus maneuver. There we had solar reflectors blocking sunlight; on Mars, we use orbital reflectors to direct more light onto the planet.

The Mars Trilogy by Kim Stanley Robinson does an amazing fictional presentation of the science of terraforming. The trilogy begins with the voyage to Mars and then follows the lives of generations of colonists. After creating and sustaining a habitat, they increase atmospheric pressure and temperature so that water can exist on the surface. This series has a lot going on from politics (within and between Earth and Mars) to the details to terraforming.

I would be remiss if I failed to mention other local options for colonies, namely the various moons of our solar system, including ours. Europa, Jupiter's largest moon, lies outside the Goldilocks zone but has water underground. To survive, colonists would have to live in permanently enclosed habitats or below ground.

With our own moon, we know that it is close, water sits beneath the poles, it's packed with helium-3 (an isotope we could exploit for safer nuclear energy), and we've been there before. At the very least, we could set up a base to mine the water and break it down into hydrogen and oxygen for use in rockets we launch to other destinations.

SEARCHING GALACTICALLY: WHAT IS AN EXOPLANET AND HOW DO WE FIND ONE?

Exoplanets are planets outside our solar system. Roughly 3,400 exoplanets have been discovered at the time of this writing.10 They are pretty far away, but I like to think that someday they might be colonized during the expansion of the human empire. Only the government I envision wouldn't be as uptight as the Alliance in the Firefly film/TV franchise.

So, how do we find these planets? Because of the difficulty in detecting exoplanets with direct imaging (i.e., by seeing them), scientists use two highly successful indirect methods.

1.Transit method

When a planet crosses in front of its parent star, the star's brightness dims a very small amount. The size of what passed in front of the star can be estimated from this decline in luminosity.

In February 2017, the existence of seven Earth-sized planets about forty light-years out in the Aquarius constellation were announced.11 Galactically, this is practically next door. All seven planets were found using the transit method. The closest three are just within the Goldilocks habitable zone. Their sun, Trappist-1, is only one-twelfth the mass of our sun and less than half as hot, so its Goldilocks zone is considerably closer.

Over the span of only a couple of days, the innermost planet zips around the pygmy (Jupiter-sized) red dwarf Trappist-1. As a shout-out to Johannes Kepler, credited as the first person to determine that planets nearer to their suns orbit faster than planets farther away, I'll mention that the farthest planet orbits at a sloth's pace of twelve days.

Astronomers measured the wavelengths of light blocked by each planet. Each gas has its own light wavelength, so eventually we might be able to determine which gasses are in the atmospheres of these planets. The exciting bit is that if oxygen is present, that might be the result of plant photosynthesis. Yes. I'm bold enough to say life, of the extraterrestrial kind.

2.Radial velocity (the wobble method)

An exoplanet exerts a gravitational pull on its sun. Granted, the pull is miniscule relative to a star, but it does have a measurable effect. The force causes the star's orbit to wobble a wee bit away from the solar system's center. The bigger the planet, the greater the wobble.

The Alpha Centauri system is composed from a triad of stars. The closest of the three is named Proxima Centauri. Circling it is a planet about 1.3 times as massive as the earth. This planet, named Proxima b, is only about 4.24 light-years away.¹² Evidence of this planet was discovered using the wobble method.

The planet is pretty close to its sun, only 5 percent of the distance Earth sits from its sun. Its orbit is only 11.2 days. Despite the short year, it is potentially habitable.

I know—how is that possible? Well, Proxima Centauri is a red dwarf, a low-mass star. That makes it cooler than our sun, so the planet's nearness doesn't create a heat problem. The projected temperature of the planet is just about right for water to flow on its surface. In chapter 17 you will learn about a project to send unpiloted ships to Proxima b.

TO INVADE OR NOT TO INVADE?

Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us.

—H. G. Wells, The War of the Worlds

How would you like it if Martians invaded the earth and transformed our ecology to suit their habitation needs? I'm sure the humans in the 1890s had a lot to say, especially when Mars attacked—at least in H. G. Wells's The War of the Worlds.

I'll reverse the question. What if we find a planet with life already on it? Do we alter the planet to meet our needs? Would you terraform if you knew it might be environmentally disastrous to life that had evolved according to its own environment? The moral issue goes past intelligent or even sentient life; it reaches all the way down to microbial life that might someday evolve into intelligent life. The cost of terraforming won't be paid only by us. The cost will also be paid by the planet we homestead.

PARTING COMMENTS

It is always sad when someone leaves home, unless they are simply going around the corner and will return in a few minutes with ice-cream sandwiches.

—Lemony Snicket, Horseradish

Thanks to evolution, humans have a special relationship with the earth. Can we divorce it and pair up with a shinier and younger planet? Yes, but not easily. The science of changing a planet into a habitable version of the earth is called terraforming. Terraforming is adding to, or augmenting, what a planet already has. For some planets, it might be as simple as adding volatiles by dismantling a small nearby moon or as complicated as directing asteroids at it.

CHAPTER 12 BONUS MATERIALS

BONUS: HOW DO WE HANDLE ALL THE RADIATION THE UNIVERSE THROWS AT US?

It might be possible to modify humans for space travel and inhabiting planets that don't have radiation shields. Our cells have the bad habit of undergoing decay and mutation when they are hit by radiation. And a lot of radiation fills space in the form of cosmic rays, high-energy particles that damage living cells. In fact, due to their exposure to cosmic rays outside the earth's magnetic field, the Apollo astronauts have been five times more likely to die of heart disease.13

A good start would be to find a way to protect our bodies from all that radiation. The solution might come from stealing a few genes from the microscopic invertebrates known as tardigrades. Because of their looks, they have been nicknamed the “water bear.”

These creatures are capable of surviving extreme conditions including dehydration and the vacuum of space. Tardigrades also have a unique protein that shields its genes from radiation. When exposed, their genes do not split apart or mutate as would the genes of most other life-forms on Earth. The protein probably evolved as a defense during dehydration, which causes similar cellular damage.

And now for the cool part. Scientists have inserted the protein into cultured human kidney cells, boosting cell tolerance to X-ray radiation damage by 40 percent.¹⁴ So it might be possible for the tardigrade protein to protect human DNA from the radiation of space. Someday our space explorers might have water bear DNA.

Fig. 12.3. Picture (illustration) of water bear tardigrade. (iStock Photo/Eraxion.)