Typically in science fiction, humanity enters space to find that it is filled with thousands of planets, all identical to Earth, waiting to be explored and colonized. However, in real life, we aren’t as spoiled for choice. Given our limited range of travel through our galaxy, and the technology of our time, what are our options? While more planets are being found all the time, there are three places right now that are major contenders for a possible colony: the Moon, Mars, or the neighboring extrasolar, or exoplanets of Kepler 62F and Alpha Centauri Bb.
To start, here is some background information of the history of these planets as options for colonization.
Earth’s natural satellite has always been the first thought when considering space travel. It was the finishing point for the space race between The United States and The Soviet Union in the 1960’s. It has been fantasized as the next home of humanity in popular culture, such as in the Robert Heinlein novel “The Moon is a Harsh Mistress” or the more recent film, “Moon”. Even during the George W. Bush administration, the United States government proposed a plan for an established lunar colony by the year 2020 (the plan fell apart after the 2008 economic collapse forced the government to cut spending from NASA). Despite these setbacks for the U.S, the space agencies of the countries that haven’t made it to the moon, such as China, The European Union, India and others have been planning their own missions.
Moon (Image credit: NASA)
If the Moon has been the first to come to mind when thinking of where to colonize, then Mars has been a close second. Although not the object of a worldwide race between rival countries like the Moon, Mars has been the subject of a decade long series of unmanned missions by the United States, most recently via the Curiosity rover, which has found evidence of frozen water.Plans have been made for a manned mission to Mars in the year 2020, with the rover missions first testing if Mars can support a manned mission.
Mars (Image credit: NASA)
Extrasolar planets, or exoplanets, are defined as “a planet that orbits a star in a solar system other than that outside of Earth”. Exoplanet systems contain the greatest chance of finding a planet that is similar to Earth in terms of atmosphere, ecosystem, or gravity. Additionally, exoplanets are being discovered at an extremely fast rate. The planet of Kepler 62F, the fifth planet of the recently discovered Kepler star system is found to have a slightly higher mass than Earth. In the relative context of planet discovery, this is a quality that draws the attention scientists. Additionally, Alpha centauri Bb has a mass similar to Earth.
Given the specificity of what humans would need to successfully live on another planet, the three factors to consider when choosing a planet to live on are its atmosphere, its gravity, and its distance from Earth.
An artists rendition of Kepler 62F (Image credit: NASA Ames/JPL-Caltech)
A crucial factor in deciding what other planet to live on is the quality of its atmosphere. Our first colony option, the Moon, has no atmosphere, which would require us to build an artificial structure to live on it. This could be both expensive and time-consuming. Mars’ atmosphere is composed of Carbon Dioxide, Nitrogen, and Argon. This would also require an artificial structure or an attempt at Terraforming, something out of the pages of science fiction. A recently discovered exoplanet, on the other hand, could have a similar atmosphere to Earth, which could both remove the factors of cost and time.
A second factor in considering where to colonize, is a planet’s distance from Earth. Given that a colony on another planet would require resources and colonists from Earth, distance is important to consider. The Moon would be advantageous in that it is only 384,400 kilometers, the closest of the three options. Mars, on the other hand, would take longer, with the distance from the Sun being 54,600,000 kilometers. Both of these distances are topped by the distance it would take to reach the nearest Exoplanet, orbiting the star of Alpha Centauri B. First, given by the fact that it is in another solar system, humanity would first have to find a way to travel 4.37 light years, the time estimated it would take light to travel there. For Kelper 62F, that distance would be 1,200 light years. Previous expeditions to both the Moon and Mars, such as the Apollo missions and the Curiosity Rover mission, have taken from 3-5 days to get to the Moon to 8 months to get to Mars.
Below is a graph showing the gravities of the four planets and the moon. We know so little about the surface of Alpha Centauri Bb, that its gravity is unknown to us.
Another part to consider is the force of that planet’s gravity. The Moon’s gravity has been measured at 5.328 ft./s2. Mars is measured at 12.2 ft./s2. The gravity of an exoplanet depends on the planet. Kepler 62F has a gravity approximately 1.4 times the gravity of Earth. The following graph gives an ample comparison of the four planets. An important factor to consider are the effects a different gravity can have on the human anatomy. Depending on the gravity of the planet, the human body would have to exert more or less physical energy than it would on Earth. This could potentially have negative effects on us: If certain parts of our body are not exercised on a regular basis, that part will atrophy (a state where an organ or other part of the body withers, weakens, and dies).
When deciding the next habitat of humanity, there is no perfect option. In terms of distance, all four options require a trip of thousands or millions of miles each. While the Moon and Mars can be reached in a short period of time, it would take thousands of years for humans to reach either of the exoplanets, unless a method of going faster than the speed of light existed. The Moon has no form of atmosphere, both exoplanets could potentially have suitable atmosphere, but their compositions remain unknown. Mars, on the other hand, has some making of an atmosphere, but it is toxic to humans. Lastly, the Moon and Mars both have similarly weak gravities, and the gravity of Alpha Centauri Bb is a mystery. only Kepler 62F has the most acceptable gravity for colonization. this all contributes to the fact that with every option has its pros and cons, giving the question of where humans could colonize an unclear answer.