The 21st century will forever be remembered as the one during which humanity became multiplanetary.

We stand at the brink of a new era in human evolution. Some would say we’re standing at a precipice. We face unprecedented global challenges while simultaneously merging into a true global culture and commencing expansion into space. Perhaps that’s the way the universe works; maybe huge challenges often or always coincide with huge opportunities. Maybe that’s the nature of planetary transformation; maybe it’s the way it has to happen. Regardless, space settlement will assuredly have overwhelmingly positive effects for our species, and will provide us with all the necessary resources to overcome any of our current global challenges, whether environmental, economic or social.

Elon Musk, CEO of SpaceX, said that human expansion into space and becoming a multiplanetary species is an evolutionary leap so great and significant that it can be compared with life crawling out of the oceans. The stated purpose of SpaceX is to be a key player in that event, and put thousands, if not millions, of humans on Mars.

But it’s not just SpaceX taking steps towards Mars. We’re seeing a general surge of interest in Mars at this time, spurred on by the recent announcements of two serious human missions. The first, Mars One, proposes to send as many as 40 astronauts on a one-way mission to the surface of Mars, where they’ll spend the rest of their lives as the subjects of a reality TV show. The second mission, Inspiration Mars, is a Mars flyby that will carry two people, most likely a married couple, to within just 100 kilometres of Mars. After more than 60 years of space agencies planning to send humans to Mars but not actually doing it, for the first time in history, entrepreneurs are taking matters into their own hands and making things happen.

But why Mars? Why not the Moon, or Venus, or Mercury? Why not just build cities in Earth orbit? Why all this hoop-la about Mars?

Mars has a feature set that makes it a stand-out champion in terms of potential settlement targets. It has an abundance of all the resources necessary to support life and technological civilisation. There’s plenty of water, carbon and metals, and energy is available from solar, wind, areothermal and nuclear sources. The length of the solar day on Mars is just 40 minutes longer than Earth’s, suggesting that humans and other Earthian species could adapt to the Martian environment with comparative ease. Mars’ axial tilt is also very nearly the same as Earth’s, giving it a familiar seasonal cycle. Another advantage, often overlooked, is that Mars is the only planet in the Solar System other than Earth with a transparent atmosphere. This gives you the advantages of an atmosphere – an easily accessible resource, effective heat distribution, aerobreaking/aerocapture – plus you can see the surface of the planet from space, and vice versa. Mars is colder than Earth, but not excessively so (it’s comparable with Antarctica), and it’s right next door. Almost everyone in the space community agrees: Mars is the target. It is the new “New World”. Even most “loonies” (lunaphiles, or Moon-lovers) agree that Mars is the next logical step beyond the Moon.

Mars will be the first planet that humans live on other than their home world, Earth.

Ideas and plans for sending humans to Mars have been proposed for many years now; at least since Das Marsprojekt was published by the great rocket engineer Wernher von Braun in 1948. As our knowledge of Mars has grown, so has our ability to believe in a future where humans live there. The more we learn about Mars and the better our technology becomes, the closer Mars becomes. And we are getting close. Those entrepreneurs who openly state their intentions to put humans on Mars are being taken seriously because most people can now see that the necessary technology, people and other resources are all available to make this dream true. It’s possible, and is happening now.

Robots vs. Humans

Many people believe that it’s preferable to send robots to Mars instead of humans because it’s cheaper and doesn’t jeopardise human lives. However, if settlement is our aim – and it should be – we must send people. In fact, even if exploration and science are our only goals, we can still achieve much more with humans.

In recent years we’ve witnessed a number of tremendous successes with robotic exploration of Mars. This effort has moved us significantly forward in our scientific understanding of Mars, how sensors and actuators function on Mars, and how to land stuff on Mars. The Mars Exploration Rovers Spirit and Opportunity have been a fascinating triumph: with an initial planned mission duration of just 90 sols (a “sol” is a Martian day, about 24 hours and 40 minutes), Spirit lasted about seven years and Opportunity is still going strong and making discoveries after 10. The landing of the Curiosity rover in 2012 was also a spectacular achievement in terms of engineering, being the largest mass (900kg) ever soft-landed on Mars.

Although much can and has been achieved with robots, humans on Mars will achieve much more. Although robots may not require air, water and food, humans offer greater cognition, dexterity, flexibility, adaptability, creativity, independence and efficiency; at least for now. The robots we’ve sent to Mars are in fact semi-autonomous, remote-controlled machines, directed by people on Earth. Astronauts on the surface of Mars will be guided by experts on Earth, but they’ll also have the freedom to indulge their own curiosity, pursue individual interests, and organise their own time and activities to a large degree.

Whether humans or robots go to Mars, the goal is for humans to gain knowledge and experience of Mars. Robots are simply a tool to achieve this, and are therefore effectively the “middle-man”. But the middle-man can be removed in order to get a better result. With humans on Mars, the experience of Mars can be obtained more directly and much more efficiently.

Robotic exploration proceeds extremely slowly and cautiously, partly because of the time delay in communications, but partly because these machines cost millions or billions of dollars to develop and send to Mars, and are therefore designed to move very slowly to ensure their survival. Every action must be considered and approved by a team on Earth before being sent to the robot. Every instruction takes between four and 20 minutes to reach Mars, and every photo and piece of data collected takes at least the same amount of time to be sent back to Earth. These machines have limited cognitive and physical abilities; if one becomes stuck in soft soil, such as what happened to Spirit, sometimes nothing can be done to get them out.

Humans will also move cautiously on Mars, but they can still move a lot faster while being careful. They can do many more things, both cognitively and physically, they don’t have to wait for instructions from Earth for every little decision, they can react in real time to unexpected events or discoveries, and if they get stuck in soft soil (for example) they can figure out a solution themselves or one of their crewmates can help them. A group of co-operating humans is functionally equivalent to a group of networked bipedal dexterous robots with strong AI. Perhaps in 20 to 40 years we can send machines to be that; or, we can just send people now.

Humans on Mars will not only deliver new information about Mars, but also the experience of Mars. They’ll be able to communicate with people on Earth in a way that robots simply cannot; they’ll be able to share emotions and sensory experiences that robots can’t have. This empathy will engage humanity with the Martian adventure and bring Mars within the sphere of our collective experience. The gates of human imagination and ingenuity will open, stimulating a flood of new ideas, missions, projects, experiments, businesses and plans, leading us directly into our dream of becoming multiplanetary.

Robots will always be part of our life on Mars. But we must send people, to more rapidly increase our knowledge of Mars, to bring Mars within the human sphere, and to commence a process of settlement.