I am vaguely surprised it was not higher rated for a rover mission. 7k meters down should do something interesting to the atmosphere if nothing else.
1. https://trek.nasa.gov/mars/#v=0.1&x=72.07800218650755&y=-42....
2. https://trek.nasa.gov/mars/#v=0.1&x=-116.4913302335018&y=16....
So if you can get 7km down without digging, that's the first place to look!
Though the person you commented on didn't refer to habitation specifically I think, just humans on the surface.
Since Mars atmosphere is 95% CO2 you're pretty much good to go there with a moderate supply of hydrogen. And conveniently enough electrolysis of water yields of course hydrogen and oxygen. And water is shockingly widely available on Mars given the regolith is 2-5% water by volume (giving the unit bastardization of 1 cubic foot of regolith = 1+ liter of water).
Most of the issues people are concerned about like radiation aren't, in reality, that big a deal. I say 'in reality' to mean that the radiation isn't enough to just give you immediate radiation sickness, so the real effect will be a probably reduced life expectancy due to greater rates of cancer. Even that isn't so clear for reason outside the scope of this post, but it's not a show stopper in any case. In general early colonists will have a significantly reduced life expectancy - it's just the nature of colonization, and always has been.
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Beyond that the Moon is a nightmare. Relatively minimal resources, 2 week long days/nights that vary between way beyond boiling hot and something close to absolute zero. No atmosphere at all so no protection against meteorites, somewhat higher radiation than Mars, and so on. There's also gravity very near zero which can pose some issues with various processes (industrial/etc).
And other destinations like Europa not only have dramatically more difficult 'local settings', but also have significantly greater distances. For instance Europa is about 10x as far as Mars and a somewhat more difficult trajectory to manage. In practice you're probably looking at upwards of 5 years for a one-way trip. We probably need to level up the tech tree a few bumps before realistically looking at things like that and Mars is a good way to do that.
Having said that, there would also be the cumulative effects of low/no gravity on astronauts. Even a year on the ISS has profound negative effects on the human body. And humans have cumulatively spent less than a month total on the moon. We have no idea how astronauts would fare on Mars for 18 months, but it would likely be very bad. And then they'd have to successfully get home.
You also have abundant toxic chemicals in the Mars regolith. Whatever technology we'd use to extract drinking water from it would have to filter out perchlorates, which are extremely toxic to both mammal and plant life. AFAIK we've never done this at all on Mars, and now we're talking about having to do it successfully for 18 months (even with water recycling). Not easy!
To be fair, a lot of proponents of human Mars exploration -- particularly here on HN -- see astronauts as essentially disposable. "Who cares if they risk dying of cancer / poisoning / suicide? It's worth it!" But if you prioritize astronauts surviving both the mission to Mars and the return home there are many, many, many unanswered questions, questions which may indeed have no good answers at all.
Before you accuse me of being a hater: I fully support exploration of Mars, and the rest of the solar system. And the best way to do so, by cost and every other conceivable metric, is with robots. Lets spend way more on space exploration, do it with probes of all varieties, and learn more in our lifetime than in all previous human lifetimes put together!
Some misleading articles (or one heinous book) try to count in-transit space weather events as part of the average to bring the numbers to the point of absurdity, but that's plainly lying. Space weather events (like solar flares) are immediately lethal if not shielded against. Fortunately they're easy to shield against since they're predictable and all settlement ships will happen to have one of the best possible radiation shields in large quantities on board - water. Similarly for perchlorates. These can be filtered out with basic water purification tech and trace amounts are even present in much of what we consume on Earth, especially in certain areas.
I'm not accusing you of being a hater, which is quite pointless. But I would say you've probably been misinformed. And I suspect precisely by one book written by a comic book artist. Somebody should probably just make a site 'clarifying' it page by page because it's chock full of misinformation and certainly a contender for the single worst pop-sci book published in modern times. It's the analog of people thinking the Moon landing was a hoax because they read some misleading article about the Van Allen Belts, all of which tend to like suggesting you'd need a radiation shield which would probably have gotten the astronauts killed due to bremsstrahlung, but I digress.
And even then, again there's just something about a trained geologist being there, immersed in the thing, thinking on the spot, using a shovel that just can't be matched with robots.
Then you have all the ISRU (in situ resource utilisation) that you can take advantage of on Mars vs. in orbit around Mars. There have been experiments already demonstrating obtaining useful stuff (MOXIE got oxygen). And theoretically you can also make methane, you can melt water, etc.
Our existing method of moving between planets (heck, even the Earth & Moon) will take 9 months to get from Earth to Mars (or back). And the launch window is every 22 months. The return to Earth is either 4 weeks after you get to Mars, or 23 months later (so any fault that prevents a prompt return means you better have almost 3 years of food/water/air onboard).
Without some magical SF technology being invented, no, we're not going to see humans travelling to Mars in our lifetimes.
If folks are serious about human trips to Mars, there would be an effort to send supply ships ahead of time and stockpiling fuel/food/water/air in orbit around Mars. This would solve 2½ problems:
1 - Carrying supplies for both directions would require building spaceships bigger than we can currently build.
2 - If there is any failure on the way or at Mars, there will be stuff to let the astronauts survive until they can fix things or any sort of rescue mission could be sent.
And "that half" - Currently, the US has had a 70% success rate sending stuff to Mars (the Soviets had 50% success). Some of those supply ships won't reach Mars orbit. Some will break on the way there and drift past Mars. Some will smash into the surface of Mars.
Why send stuff? Supplying the astronauts on ISS requires sending 1000 pounds of stuff per person per month. And that's only 300 miles from Earth. And the ISS has water recycling, yet they still need water sent up.
My estimates for a successful "manned" trip to Mars (and return them safely to Earth again) would start around $200 billion.
https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
https://en.wikipedia.org/wiki/Launch_window
This page claims Earth/Mars launch windows are every 26 months:
https://en.wikipedia.org/wiki/Exploration_of_Mars#Launch_win...
So you are telling me we could have gone to Mars and back a few times instead..
But there's places like the araneiform terrain where you likely get much higher transient pressures, and maybe they create enough of a greenhouse effect to warm up before they burst through the CO2 ice crust. They'd be a great way for life to spread mechanically using those pressurized bursts.
Sounds like the Martian mantle is (or was) organized as a single giant convection cell, with the upwelling under the volcanoes and sinking at Hellis Planitia.
Effects of 7km upon the atmosphere seem easily predictable. Ditto the benefits of 7km for exploration - improved aerobraking, drone performance, etc. But not so predictable would be effects on the subsurface.
An obvious downside of 7km would be "better" air cooling of equipment that needs to stay warm during Martian nights.
Also, whatever caused the Noctis Labyrinthus (west side of the valley in the article south east of the volcanoes) is a wild geologic process I don't think I have seen anywhere else. The large valley looks sort of like a rift valley, and erosion canyons are obvious, but Noctis Labyrinthus with it's fragmented plate look is weird, my best guess is a rift valley where three plates are separating, but that is a weak guess.
Really the fact that the jpl was able to fly a helicopter at all in mars's weak excuse for a atmosphere was an engineering flex like I have never seen.
But visually, it's even less, because Mars is smaller than earth, so its curvature matters.
And Mars, with giant volcanoes and credible evidence of recent* vulcanism, obviously has more options for causing quakes.
*"Recent" in the geologic sense - https://en.wikipedia.org/wiki/Volcanism_on_Mars#Potential_cu...