Going to the Moon is a bit like going south with Ernest Shackleton to the Pole, or rowing across the Atlantic in a dinghy. Such endeavours may take a great deal of courage, effort and dedication, but the reasons we undertake these dangerous feats remain unclear. Doing them twice is even harder to understand.

We need satellite technology to communicate, forecast the weather and monitor global warming. Absent advanced robotic technologies, this may require an occasional direct human presence in Low Earth Orbit. Nasa points to “spin-offs”, or technologies that benefit life on earth and justify space exploration. Freeze drying, cordless vacuums, enriched baby food and scratch-resistant lenses were all pioneered through space travel.

But no human ever needs to go deeper into what Aldrin called the Moon’s “magnificent desolation” in order to drive technological innovation or economic growth. The story of the Apollo mission is not primarily one of economic efficiency or technology, but something deeper and more human.

Consider Richard Branson, for example. To date, his promotion of commercial space tourism in sub-orbital flights has been an enormous hole into which he has poured a great deal of his own money and that of other investors. So why has Branson persisted?

No doubt he would like to make money eventually, and one day his company, Virgin Galactic, may do so. But part of his motivation is more difficult to explain. It transcends economic reasoning. Branson wants to go into space, and he wants others to have this same opportunity. What does he hope we might gain from doing so?

To understand the reasons for space travel, we can think of it according to three lines of argument: one ethical, one educational and one colonial. The ethical argument goes like this: we need a new frontier, or a grand challenge to focus on, in order see humanity and the Earth from a different perspective – to understand our own planet as one small rock within a larger system, and to comprehend the enormity of the universe beyond it.

Seeing the Earth from space has impacted positively upon the worldview of a number of astronauts who speak of an “orbital perspective”, or “overview effect”. The astronaut Ron Garan has described his experience of an gazing out of a window International Space Station at the Earth and reflecting on the need for an interconnected response to global problems. Perhaps all world leaders should be exposed to this feeling.

But the psychological benefits of viewing the Earth from orbit don’t automatically produce advantages elsewhere in space, especially when we begin to think about issues such as mining and political control. Conflicts over key resources on the Moon and Mars are likely to reproduce terrestrial problems rather than overcoming them. These outer-space ventures are as likely to produce acrimonious divisions as they are to produce universal harmony.

The educational argument centres on the advancement of human knowledge, particularly scientific knowledge. This may come closest to what the prominent space ethicist James Schwartz calls “myth-free space advocacy”, where we neither over-estimate the commercial potential of space or appeal to questionable ideas of human destiny. The big prize here is knowledge about life itself. We currently have only a single example of the emergence of life on earth to work from. Yet there are many other places where life could look very different, and the discovery of historic traces of microbial life could be a seminal moment in human history.

The scientific community is divided over how necessary an actual human presence in space is for education or research. Keeping humans alive in space is a complex and expensive business, and there will likely be far cheaper and more viable robotic alternatives in the near future. Moreover, science may even benefit from maintaining conditions in outer space that are untouched by a human presence. If we discover any evidence of life, we will want to make sure that we didn’t bring it there ourselves.

Most of the media commentary around modern space travel hinges on Elon Musk’s desire to back up the biosphere on Mars and Jeff Bezos’ talk about limitless capitalist expansion with millions of humans living in free-floating space structures. This brings us to the third argument for space travel: colonisation, or settlement. But given that there is nobody out there in the solar system for us to colonise, “colonisation” may be a misleading term.

Suggestions that we could find a backup planet for life on Earth may also be confused. We cannot literally back up the biosphere. Conditions on Mars will always be very different from those on Earth. On Mars, gravity is only a third of the strength of gravity on Earth; it’s strong enough to hold us to the surface, but the difference will affect the growth patterns of animals and crops. Temperatures on Mars swing from the equivalent of a warm day in Scotland to 100 degrees below freezing point, even at the equator.

But there’s a possibility that Mars and a limited number of other surfaces within the solar system could sustain life. This possibility could perhaps be enough to justify the idea that the Earth has a duty to extend life to such places – if the universe is in some way better with life in it. Our activities in space could then be what Harvard astronomer Martin Elvis calls “a vector for life”, when no other life or vectors for actual life are known to exist.

The trouble with the idea of a vector for life is that it provides little justification for the flags and footprints of the first visit to the Moon, let alone the grander visions of human settlement in space. Putting humans back onto the lunar surface, or onto the surface of Mars, may be acts with powerful symbolism, but the spread and consolidation of life is unlikely to be in a human form. Though we may one day be able to send microbial forms of life to other galaxies, we cannot send people across vast distances in space without condemning them to death.

Ultimately, our duties end with what we can do. And while a handful of humans may soon return to the Moon, at most we have reason to propel basic forms of life beyond our solar system. We may hope that it will not be lethal to any unknown but indigenous life elsewhere. And we may cherish the thought that, in some place far away, rudimentary signs of life might one day evolve into sentient beings.

Tony Milligan is a teaching fellow in ethics and the philosophy of religion at King’s College London. He is the author of Nobody Owns the Moon.

This article is part of the Agora series, a collaboration between the New Statesman and Aaron James Wendland. Aaron is Assistant Professor of Philosophy at the Higher School of Economics. He tweets @ajwendland.