Recently, the Trump administration discussed sending astronauts back to the moon, instead of on the Mars. It is well known that Space-X would like to send people to Mars. This has brought up a debate about whether the moon or Mars would be better to colonize first. Mars should obviously be the winner here, since, you know, Mars is awesome, but I thought that it would be interesting to look at both sides from a number of different points of view.
First let us look at advantages for Mars:
1. Mars spins at a pretty reasonable rate. Its day is just over 24 hours, so a day on Mars will be roughly a day on Earth. A day on the moon is 28 Earth days, which will take a fair bit of adjusting too. There is no need to readjust on Mars. Also, because Mars’s day is relatively short, the day-to-night temperature difference is not too dramatic, while on the moon, the day is very hot and the night is very cold. There is an almost 300C degree temperature difference between the day and night temperatures on the moon. Yikes.
2. Mars has an atmosphere. Not really a great atmosphere, but some atmosphere. It is all Carbon Dioxide (well, not all, but a hefty bit), which is great for plants, but really sucks for us humans. The atmosphere allows wind to blow, which helps to equalize the day-to-night temperature differences, but causes a lot of dust to move around too. We can pressurize domes and structures using air from outside. Having some atmosphere is better than not having any, which is roughly what the moon has. The side of the moon that is facing away from the Sun (the literal Dark Side of the Moon, not the metaphorical one), is one of the more vacuous places in the solar system, since the solar wind of the sun just plows into the moon, which leaves a giant wake of nothing behind it. We think of space as being pretty empty, but there are something like 12 orders of magnitude more particles per square meter where the International Space Station flies than on the dark side of the moon. That is pretty empty. (And dark – remember that the night lasts for 14 days on the moon!)
3. Mars may have a lot more water than the moon. There would only be certain places we could colonize on the moon and have easy access to water, while water may exist in the subsurface all over Mars. This is not really definitive, but is a relatively strong possibility. Of course, Mars doesn’t have much Oxygen to breathe in the atmosphere, but, hey, neither does the moon. We can make Oxygen out of water, though. So, it may be easier to sustain life on Mars, simply because of the (possibly easy) access to water. On the moon, we would have to live near the poles, which is probably ok, since you might not have as much of a day-to-night temperature difference.
4. Mars’s atmosphere could stop a bunch of harmful EUV and energetic particles from the sun. This would stop you from frying if you went outside. The moon doesn’t really have anything to stop you from getting zapped (technical term). So, really, you would have to definitely live in caves on the moon, but on Mars it might be possible to live above ground. You would still get a lot of radiation exposure though.
5. Gravity on Mars is much larger than the gravity on the moon. This keeps the atmosphere on the planet, and would help us keep things down on the ground and keep our bones a bit more robust.
6. Mars is really cool. It is red, and there are gods named after it (or it is named after a god? Not sure which…) Mars is capitalized, while the moon is not. Clearly, Mars is better. Heck, life could have formed there, then been transported to Earth and flourished here. So, if you are interested in science, Mars wins.
Advantages for the moon:
1. The moon is really close to Earth. In fact, it is orbiting Earth. So, we don’t actually have to leave the Earth system to get to the moon. This saves a HUGE amount of fuel (money). We have rockets right now that can land a lot of stuff on the moon. Like, we could start dumping supplies on the moon in months if we really wanted to. We would have to do a lot of research to really dump an equal amount of stuff on Mars (i.e., years away). Don’t get me wrong, we do have rockets that can land tiny amounts of stuff on Mars, but that is tiny. We had been talking about a sample-return mission to Mars, but NASA has basically dropped it, since it would be about $20 billion dollars, and we find Mars rocks quite often. It is really hard to get big things to Mars, while it is much (much) easier to get big things to the moon.
2. It only takes 3 days to get to the moon, while it takes 6 months to get to Mars, and you can only do that every 2 years. If you miss the two-week launch window to get to Mars, you have to wait another 2 years. In the two-week launch window to go to Mars, we could literally go to the moon and back. If we need to rescue people from the moon, it would only be a few days, while on Mars it could be years. Remember the movie “The Martian”??? Also, if you want to have a conversation with someone on the moon, it would only be a few seconds of time delay, while the delay to Mars is between 4 and 24 minutes, depending on whether Mars is on “our side” of the sun or the opposite side. Imagine trying to have a conversation with someone with a 24 minute delay. Ugh.
3. Because the moon is much smaller than Mars, it is easier to get stuff down to the surface and back up into orbit (i.e., it takes less fuel and therefore less money). In fact, shipping stuff from the moon to Earth is very, very cheap (read the Robert Heinlein book, “The Moon is a Harsh Mistress”) . So, if we mine the moon, we could get stuff back to the Earth for almost no cost at all. If we mined Mars, it would be incredibly expensive to get it back to Earth (harder to get off the planet, and it is much further away). So, from a purely commerce oriented stand point, a moon colony is a much better economical venture.
4. Remember the 6 month trip to Mars? That is on a tiny ship out in the vastness of space. If there were a large solar event that caused the radiation to increase significantly (happens a lot), then you would die unless there was significant (very heavy) radiation shielding on the ship. The space between here and Mars is not friendly at all. This is true of the space between here and the moon too, but it is only 3 days to get there, so it is easier to avoid times in which there may be bad solar events.
5. Earth-rise. That would be awesome. Unless Earth was a nuclear wasteland. Then it would just be a reminder of what used to be.
So, in summary, Mars is a nice idea, and could probably sustain life better and provide a much better scientific exploration opportunity, while the moon is a much more economically feasible location for a colony. Because of that, Mars will continue to be far off in the future unless the funding and political winds shift. If something horrific happens on the Earth, and it can no long sustain life, then Mars is probably a much better place to live because of the possibility of finding water, its higher gravity, and its atmosphere. The moon is a bit too harsh to be anything but a temporary stepping stone to the future.