How Will We Colonize Other Planets?

Ever since the Apollo program put the moon within our reach, establishing a lunar outpost has seemed a logical next step. Earth's natural satellite offers several advantages over more distant destinations, such as Mars or Saturn's moon Titan. First, it's relatively close, which means crews could get back and forth from the Earth and moon in just a few days. Additionally, a lunar base would enable use to learn a lot about the effects of low gravity, isolation, high doses of cosmic radiation, and disrupted circadian rhythms on human space colonists — knowledge that would be invaluable when we eventually venture to other worlds [source: Fecht].

Additionally, the moon's low gravity and closeness to Earth would make it an ideal location for a spaceport from which astronauts could embark on missions to Mars and worlds even further away. And in terms of long-term possibilities, the moon is a big place — its surface is roughly the size of Africa — and it has plenty of room for human colonists [source: Gent].

But living on the moon won't be any picnic. With no atmosphere, it experiences huge temperature extremes, swinging from minus 298 degrees Fahrenheit (minus 183 degrees Celsius), at night, to 224 degrees Fahrenheit (106 degrees Celsius) in the daytime at the equator [source: CalTech]. Its surface is also peppered constantly by micrometeorites and cosmic rays [source: Redd].

To survive those hostile environmental conditions, some experts think that colonists will likely have to place their habitats under the lunar soil or at the base of a lava tube [source: Redd]. Others envision domes built by robots equipped with 3D printers, which would provide protection [source: Gent].

Then there's the issue of food and water. In 2018, a team of scientists spotted the first definitive evidence of water ice on the lunar surface, a discovery that suggests that future lunar colonists might be able to extract their own supply, which could provide water for drinking and for irrigating plants in lunar greenhouses, as well as a raw material for rocket fuel [sources: NASA, Grush].

NASA's current plan for returning to the moon involves building a lunar orbital station, the Gateway, which will serve as a staging area for teams of astronauts to make short visits to the lunar surface. The first part of the Gateway is scheduled to be sent into space on a private rocket in 2022 [source: NASA].

Keep reading to find out what the plan is for Mars.

Some space experts have argued that NASA should focus on going to Mars instead of returning to the moon. But President Trump's appointee as NASA chief, Jim Bridenstine, has reassured Mars proponents that despite Trump's switch to prioritizing a lunar mission, the space agency still intends to go to the red planet. Bridenstine has said that returning to the moon will enable the agency to develop technologies for an eventual Mars mission, including "precision landing systems, methane engines, orbital habitation, surface habitation, surface mobility, long duration life support operations and much more" [source: Smith].

Since NASA's December 2017 shift to focusing upon returning to the moon, it hasn't put out any updated plans for making a manned landing on Mars and establishing a human colony. But in a plan that the agency published in 2015, the initial mission would be complex. Astronauts would make the 180-day trip to Mars in a crew habitat module, a two-level container that would double as a habitat on the Martian surface. By the time the astronauts landed, a separate laboratory module, a rover vehicle and other equipment — including a nuclear reactor — and supplies already would be waiting for them on the Martian surface, after being transported there by robotic spacecraft. Another spacecraft, fueled for a return to Earth, would be positioned in orbit to enable the initial crew to eventually return to Earth [source: NASA]. Subsequent missions might expand that original base or set up others to form a Mars colony.

On Mars, human colonists would have to grow their own food. NASA has been experimenting with growing vegetables on the International Space Station, and also has developed simulated Martian soil, which contains nutrients that plants would need to survive, to better understand how it could be used to grow crops [source: NASA].

Over the years, science fiction writers and futurists have speculated about the possibility of terraforming Mars, to transform its environment to something closer to Earth's. One approach would involve releasing carbon dioxide trapped within the Martian surface to make the atmosphere thicker, which also would help to trap solar radiation and warm the surface. However, a NASA study published in 2018 concluded that the Martian surface doesn't contain enough CO2 to be put back into the atmosphere to create a greenhouse effect, and it wouldn't be possible to extract much of what is there with present technology [source: NASA].

In the next section, we'll talk about the possibility of colonizing an asteroid or dwarf planet.

Asteroids — those rocky objects that orbit the sun in a wide band between Mars and Jupiter — could serve as stepping-stones to the outer planets. There are only 100 asteroids larger than 125 miles (200 kilometers) across, but a billion or more may exist, making them one of the solar system's greatest resources [source: Rees].

But colonizing an asteroid would be even more challenging than building a base on Mars or the moon. Asteroids don't have much gravity, so astronauts would face serious health problems from living in that environment unless they created artificial gravity inside the base, possibly by continually spinning the entire habitat.

Because the asteroid belt is so far from the sun, solar arrays that powered such machinery would have to be gigantic. There also would be the problem of shielding the colonists from cosmic radiation. You might think that tunneling into the surface might provide some protection, but doing that would be tricky, because a lot of the objects that we call asteroids aren't actually solid rock, but basically bunches of space junk without much structural integrity [source: Allison].

But if we were going to colonize a smaller distant object, the dwarf planet Ceres, the largest object in the asteroid belt and the only dwarf planet in the inner solar system, might have some possibilities. NASA's Dawn probe discovered that the asteroid has an outer shell that's rich in water, in the form of ice and hydrates [source: NASA].

The Obama administration had an ambitious plan, the Asteroid Redirect Mission, which called for capturing part of an asteroid and bringing it back to the vicinity of the moon, so that astronauts could land on it and retrieve samples. But the project was cancelled in 2017 by the Trump Administration [source: Malik].

Are you ready to head beyond the solar system?

If we're going to colonize a planet in another star system, we have to answer two questions. First, do any Earth-like planets even exist outside of our solar system? Thanks to NASA's Kepler telescope, the answer to this question is yes. Kepler, which was decommissioned in 2018, located nearly 2,700 planets — what astronomers call exoplanets — orbiting stars anywhere from a few hundred to a few thousand light-years away. Many of the exoplanets are gas giants similar to Jupiter and Saturn. But others are "super Earths," rocky planets slightly bigger than ours [source: Howell]. Some of those might possibly have the right conditions to be hospitable to human colonists.

The second question is purely logistical: How do we get to a planet located trillions of miles from our own? To answer this question, scientists will have to rethink space travel. For example, the idea that a single crew will fly to a remote planet is highly unlikely. Instead, spacecraft might need to carry family groups capable of living in space for generations [source: Feltman].

Scientists will also have to come up with better propulsion systems to cut the travel time. Nuclear fission- and fusion-based engines might be feasible, but more likely candidates include solar sails, ion-propulsion systems or antimatter rockets [source: Stromberg].

Light sails work by directing laser light onto a huge aluminum-foil sail. As photons strike the sail, they transfer momentum and push the sail forward. Ion-propulsion systems use solar panels to generate electric fields that accelerate charged atoms of xenon. Such an engine powered the Dawn mission, which hurled an unmanned spacecraft to two asteroids, Vesta and Ceres, before its mission was completed in November 2018. Antimatter rockets are the most efficient and achieve the highest speeds, but the technology is relatively untested. Such a rocket mixes equal amounts of antihydrogen and hydrogen, which annihilate each other in a combustion chamber to release enormous amounts of energy [source: Stromberg].

In the end, a combination of technologies may be the solution, proving once again that conquering deep space will require cooperation and collaboration among scientists of different disciplines and nationalities.