Sending humans to Mars seems less attractive to me than sending robots to Ceres. Is there an argument for Mars that doesn't include the phrase "multi-planet species"?
Mars has a more terrestrially-similar gravity level.
Mars has way more solar power.
Ceres is basically vacuum, can't aerobrake. And its gravity well is so small you also can't take advantage of the Oberth effect.
Mars' atmosphere shields you from the vast majority of solar radiation (so no risk of death from acute radiation poisoning), from all micrometeorites, and even a significant amount of galactic cosmic radiation. It also provides global access to gaseous CO2, nitrogen, argon, and even some water vapor.
Mars can be terraformed.
Two questions:
1) How exactly does this work, when the mean surface temperature on Mars is below freezing? [0] I don't know a lot of plants that can grow very well in below freezing temperatures with a ton of CO2. Evergreen trees come to mind, but you won't find too many of them above the arctic circle.
2) If we cannot even properly manage the atmosphere on our own planet, why do you think we'd fare any better on another planet?
To put it another way: why aren't we aggressively working to terraform Earth back into a usable state than talking about doing this on another planet where resources are much more limited and everything needs to be built locally or shipped in from another planet?
[0] https://www.space.com/16907-what-is-the-temperature-of-mars....
Mars is a barren desert almost a vacuum. But no one lives there, so political opposition is less of a problem in principle. Besides, I think we'll solve the Earth's problems, too. Hopefully doesn't require extreme geoengineering like Mars does, but that's possible.
The idea is you start a self-sustaining civilization on Mars /first/ that has sufficient industry to do terraforming on its own. It will have a strong cultural and political interest in doing so. The hard part is getting a self-sustaining civilization (a city of at least a million people).
Terraforming Mars would involve pumping super greenhouse gases into the atmosphere, warming the surface by reflecting sunlight from massive (but extremely thin) mirrors in orbit, modifying the surface albedo by placing dark colored dust on the poles, and perhaps more directly by continuous sequence of fusion pulses (think inertial confinement fusion) over the poles as Musk has previously suggested. This all would cause the regolith to outgas and increase the atmosphere's pressure which should lead to more warming. Might need to beef up its atmosphere further with external source of volatiles, like icy asteroids or comets. The impact would also liberate a lot of heat itself.
Obviously this is engineering on an extreme scale and long timeframes.
First off, in the 'backup' argument Mars isn't meant as a bomb shelter for the human species. It's a shelter for human civilization, which is a higher level and much more fragile thing. Think about the libraries of the Arab world, not "The Arabs have to exist or humanity could die out when Rome falls!"
The other argument is as a launchpad. Mars is halfway to anywhere in the same way low earth orbit is, but Mars comes with exploitable resources. In the future, we can debate whether those resources are better exploited by enormous robotic fleets and autonomous systems or with humans on site, but with current tech readiness levels nothing beats in-situ humans for adaptability. A strong Martian industrial base will produce huge returns for terrestrial society. From dense high-throughput communication networks to massive orbital manufacturing depots to idyllic ring-world habitats, everything we want to put in orbit is cheaper starting from Mars.
They're only just proving this out, but one of the theses behind Made in Space [0] is that there are all sorts of microscopic manufacturing processes - optical components and chips being the most obvious - which would benefit from manufacturing in an ambient gravity between 0-1g. Which you simply can't get on Earth.
The argument for space-based industry has to start with economics, where it's cheaper because it's closer to the raw materials (asteroids) or closer to the consumers (Mars, lunar, and orbital habitats). The elimination of dirty industry from Earth would only come about as a far-downstream side effect of a well-developed space economy that makes it cheaper for Amazon to drop a Kindle on your house from orbit that it would be to manufacture it in China.
* Human capability >> robotic capability
* Mars as a very long term "Backup Earth"
* If you can go to Mars with humans you can go to the Moon with humans as well.
* Human capable systems can also carry robots, the reverse is not always true.
1) If we can live on mars, we can live on whatever state earth would be in, even if it was mars-like.
2) If earth becomes unlivable, the exhaustion of resources would mean we'll never be able to get to mars in the first place.
Either way, I just don't see a mars colony happening as anything except a temporary experiment. It's a really hostile environment.
And in the case that "multi-planet species" is the goal, is there a better target? I'm not aware of one.
Yes. I don't see what concrete benefits we gain becoming such a species, and I doubt it's possible to send live humans to Mars, or suspend life there. This is the new alchemy.
By the actual definition of alchemy, sending living people to Mars can't qualify as such: we know for a scientific fact that it's possible. It's not even particularly challenging to successfully send (and land) living people there, it's extremely dangerous and risky to their well-being to do so. The idea is to not kill a lot of people in the process of attempting it.
Mars is also a more hospitable place; it has gravity, atmosphere, water, etc.. It's possible to create methane fuel on Mars.
There are also more reasons for people to want to visit Mars that aren't motivated by becoming a multi-planetary species. For instance: science, tourism, entertainment (sports, movies, reality TV, whatever), and low-gravity benefits for people with mobility issues who would be stuck in a wheelchair in Earth gravity.
That isn't to say we can't or shouldn't go to Ceres as well.
1st result) Ceres - Non-profit organization in San Francisco, California
3rd result) Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter.
Colonizing Mars is, by comparison, vastly cheaper in blood. Just not in treasure.