Humanity has some unfinished business with the Moon.
The lunar surface has fallen back into the realm of the remote and unfamiliar for too long. The Apollo landings kindled a dream of an expansive, space-faring future for our species, and that vision continues to inspire us nearly a half century later.
Though we have sustained an ember of that dream through crewed missions to the International Space Station, it diminishes a little with every passing year that we do not once more step foot on another world. NASA’s upcoming plan to establish a sustainable human presence on the Moon via the Artemis program, therefore, constitutes a long-overdue reunion.
Every human on Earth has access to a night sky that is punctuated by the presence of our Moon. On a clear evening, it is visible from both dense urban environments and secluded rural landscapes. Whether we own a telescope, or have only our eyes to stargaze, it is there for us all to consider with wonder.
When we can look up at that jewel of the commons and know that it is within the reach of human experience once again, countless lives will be enriched.
There is, however, a significant inherent risk in returning to the Moon. I’m not referring to the physical hazards faced by the astronauts who will make that voyage, but rather the risk to our future security and development as a species, should that endeavor cost us our chance at Mars.
For the sake of the long-term survival and growth of life from Earth, the overarching goal of space exploration must be the pursuit of a multi-planetary future. By far the best candidate for this endeavor is Mars. The window to the red planet is open now, but given the unfortunate volatility of human history it could close at any time. The choice to insert the Moon as an intermediate step is therefore a substantial gamble.
The true efficacy of a lunar foothold, then, will be determined by whether it constitutes a commitment to that more pressing objective, or a distraction from it.
But why is Mars so essential to a multi-planetary future? The Moon is just a few days’ travel away – doesn’t that make it a more suitable choice for exploration and settlement?
A world of difference
The Moon has no appreciable atmosphere. Besides a thin layer of rarefied gas, it is engulfed by the vacuum of space. This means that the lunar surface has no protection whatsoever from radiation or meteoroid bombardment.
The lunar surface is covered with a layer of jagged particles generated by micrometeorite impacts. With no wind to erode this asbestos-like dust, it remains sharp, like tiny broken pieces of glass. In fact, it is so abrasive that it stripped away layers of the Apollo astronauts’ boots.
In sunlight, temperatures reach 260 degrees Fahrenheit (127 degrees Celsius) and, in the shade, they drop to -280 degrees F (-173 C). These temperature extremes are highly localized since there is no atmosphere to equalize the difference. Lunar equipment and infrastructure will therefore have to resist both freezing and overheating depending on whether they are in sunlight or shadow.
Artemis astronauts will experience 17% of Earth’s gravity on the Moon. The long-term effect of partial gravity on the human body is unclear, but we do know that the weightlessness felt by humans on the International Space Station results in tangible changes to their physiology, such as bone loss or muscular degeneration. It’s safe to assume that similar health consequences might result from long-term lunar habitation.
Furthermore, a day on the Moon is 29 times longer than a day on Earth. This drastic departure from our natural day-night cycle will introduce an additional challenge for our biological systems which are finely tuned to the daylight hours of our home world. The long lunar nights will also hinder the usefulness of solar power.
None of these challenges are insurmountable. We can, and should, carve out a sustainable human presence on our closest celestial neighbor (eventually), but the Moon is a dismal candidate for our next home.
Fortunately, our solar system contains a far better match for our technological and biological systems. It’s a bit of a fixer-upper, and it takes a few months to get there, but the red planet’s presence within our reach is nothing short of spectacular luck.
Home Is Where the Atmosphere Is
Today Mars clings to a thin atmosphere which has been blowing away in solar wind for millennia – however, it was once thick enough to support a warm, wet environment and possibly even life.
Despite the fact that it is presently only 1% the density of Earth’s atmosphere, the difference between some and none is significant. In the near-term, it will provide an invaluable resource to Martian explorers and settlers, who will convert ambient carbon dioxide into valuable oxygen and fuel. It will offer moderate protection against solar radiation and meteoroids, and eventually it can be restored to its previous thickness through terraforming and countermeasures against solar wind.
It is also in part due to the presence of an atmosphere that temperature variability on Mars is far less extreme than on the Moon. NASA’s InSight lander recorded the average daily air temperature of the Martian equatorial region for years. At its coldest, it dipped to around -148 degrees Fahrenheit (-100 Celsius) and the balmiest days peaked somewhere near 32 F (0 C).
The red planet is very cold, but a 180 F (100 C) temperature range is far more manageable than the drastic, 540 F (300 C) fluctuations of the lunar surface. Developing systems and procedures at-scale to accommodate a consistently cold environment is vastly more achievable than engineering against both freezing and overheating.
Additionally, whereas the cold extremes on Mars are certainly well beyond the tolerance of an unprotected human, the average global temperature of -81 F (-63 C) is comparable to the coldest inhabited regions of Earth.
(Then again, as a Canadian, my optimism regarding the extreme cold might be called into question.)
A day on the red planet, known as a sol, is just slightly longer than a day on Earth, at 24 hours and 40 minutes. This familiar day-night cycle will be essential in regulating the circadian rhythms of both humans (for healthy sleep) and plants (for successful growth cycles). This also drastically improves the feasibility of solar power relative to the Moon.
Mars also has an enormous volume of water. Though mostly trapped in ice, there is enough to cover the entire planet to a depth of 35 meters, and to sustain a civilization for the foreseeable future.
Eventually, large-scale farming will be achievable because Martian regolith contains the requisite nutrients for agriculture (once relieved of its troublesome perchlorates.) It can also be converted into strong bricks for construction simply by compressing it mechanically. Just as our first cities on Earth took form using mud bricks, so too might our initial surface structures on the red planet.
We have good reason to believe that expansive lava tubes exist below the surface, which – once reinforced by adapting construction techniques we’ve been practicing for centuries – might offer excellent protection against surface radiation and dust storms.
Lastly, the partial gravity of Mars might be problematic, but this is uncertain. We may discover that 38% of Earth’s gravity is sufficient for our bodies to adapt. Regardless, there is already promising research into possible countermeasures, and we can certainly assume that with more than twice the gravity of the Moon, the red planet’s habitability is far superior in this regard as well.
A Means to An End
I await our return to the lunar surface with mixed emotions.
Whereas I look forward to sharing in the wonder experienced by my parents’ generation as they witnessed the Apollo landings, I cannot help but worry that this renewed focus on the Moon (and resulting delay of our journey to the red planet) might cost our descendants their chance at the stars.
There is value in establishing a permanent human presence on both the Moon and Mars, but only the red planet has all the vital elements necessary to host a self-sustaining branch of civilization, and therefore to usher in a multi-planetary future.
At this moment in history, our world is stable enough that we can do things like train aerospace engineers and launch rockets. This was not the case a century ago, and it might not be the case a century from now.
The choice to delay our journey to Mars by first returning to the Moon tacitly assumes that this window will stay open long enough to achieve both goals in sequence. Though hopeful, this supposition constitutes nothing short of a gamble on the future security and growth of our species. This is particularly true given that a direct journey to Mars has been achievable for some time, and is rapidly becoming even more feasible.
Our national space agencies tell us that the Moon will be used as a testbed for technologies in preparation for Mars. Given the substantial difference between the two, however, it is difficult to see how systems designed for one might carry over to the other, without significant alteration and duplication of effort.
Further, given that the current Artemis architecture unnecessarily relies on the staggeringly over-budget, endlessly-delayed SLS rocket, and introduces the baffling overcomplication of an orbital outpost, it is difficult to imagine that the new lunar program will be carried out with any sense of urgency.
Are we going back to the Moon with the zeal and determination that got us there in the first place? Will the next human footprints on the Lunar surface be our first steps on the path to Mars, or will they bog us down in a quagmire of obstructive redundancy?
On the day that we can look up at the Moon and know that it is once again host to our species, I will smile, but my focus will quickly return to that pale red dot where the outcome of all our hopes ultimately lies, and I will worry, and I will wait.