Near identical axial tilt to Earth, meaning a similar seasonal cycle (none on the moon).
Day/night cycles near identical to Earth differing by less than an hour (2 week long day/nights on moon).
A land surface area near identical to Earth's land area, which means room for vast expansion. (moon is a bit more than 2x Russia)
Somewhat more tolerable gravity at 0.38g compared to .17g on the moon.
Vastly more tolerable temperature ranges. A day on the equator in summer can get up to around 70 degrees F, though nights hit -100 F. The large difference owing to no atmosphere. The moon ranges from nearly absolute zero at night, to greater than boiling during the day.
And many more. These are just a handful off the top of my head.
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And some would consider the distance to be a feature, not a bug. It creates a necessity for a large degree of self sustainability which is ultimately a prerequisite to becoming a multiplanetary species. On the Moon, self sustainability not only more challenging, but ultimately not really necessary given it's just a stone's throw away from a resupply. And necessity really is the mother of invention.
Ultimately I also don't even view Mars as a goal (though it may be able to over millennia developed into an amazing place, and I would be the first to sign on for a mission to such), so much as a stepping stone. By the time the first human settlement is established on Mars, we should be looking outward from there as well. Titan being a possible next destination.
The moon also offers a way to develop self-sustainability. When you've got "oops I forgot the ketchup" it's only 2 days away, not years. Far more people will be willing to spend a few weeks on the moon than several years to Mars.
If fuel and machinery can be made on the moon, with its lower gravity well, it becomes far more practical to build big ships to go to Mars and elsewhere.
That would all be outside. Polypropylene is proof against sulfuric acid.
But you will need that sulfuric acid for the hydrogen it carries. Carbon from CO2 for structural members, hydrocarbon for plastics and fabric for gas bags, oxygen to breathe. There is thin gaseous silicides, in case you need any silicon.
It will be hard to keep the concentration of CO2 in the breathing air thin enough not to make everyone stupid, with so much of it outside.
Sabatier reaction plus ordinary rain will solve that problem away but nothing will solve the slow rotation rate and lack of a molten core and resulting magnetosphere. Still Venus is a better candidate than Mars for terraforming.
What if we terraformed Venus by shipping the CO2 to Mars? That way we'd be terraforming both planets.
I've been wondering about the feasibility of self-replicating floating comet factories that make dry ice comets that could be launched to mars. You could even wrap them in some sort of carbon based exterior to prevent them from boiling off too much in transit.
It would be more efficient just to redirect some comets. There is more then enough of everything floating around the inner solar system, and the Oort cloud has even more.
The composition of Mars' atmosphere is less important then getting the pressure right - at 1 atmosphere, humans don't need suits just respirators, and Earth-microbes will be more then happy to normalize things to suit them (they did it here, after all).
For Venus the big problem is water: Venus is dry. The reason it's in run-away greenhouse is because all that CO2 just will not precipitate into carbonate minerals, which to do so needs water. Again: something comets have plenty of.
The difference between the two in suitability though is the tidal lock: Mars has a day-night cycle. Venus has a day-night cycle but it's 116 Earth-days long - half the planet, if you got the atmosphere under control, would be in a freezing night for 3 and half months. You could settle it, but life would only really survive at the polls. While we can process a planetary atmosphere with plausible near-future technology and local resources, there's no known way we could "spin up" Venus (ironically a fully-tidally locked planet would have much more usable surface area as an oculus-world).
The amount of water available in comets is laughably inadequate to fill Venus's shortfall. But anyway its day length would make it very close to useless to try to terraform.
Shipping in enough hydrogen from (say) Neptune might be possible in principle using billions of automated, self-reproducing nuclear powered spacecraft.
If its atmosphere could be precipitated and the carbon freed of oxygen and somehow permanently protected from runaway combustion, the planet's low (2.64°) axial tilt and solar proximity might make a polar existence possible. But the overwhelming excess of oxygen would need to be removed or bound up in water. (The carbon might then be safely kept under water. Or, be crystallized out as diamond, which is hard to ignite.)
Quadrillions of aluminum foil balloons full of nitrogen bobbing in the stratosphere might suffice to bring temperature down.
Perhaps surprisingly, the present 3.5% of its atmosphere that is nitrogen is more than Earth's total.
As noted elsewhere, Venus's magnetic field is not much like Earth's, although it stretches almost to Earth's orbit, and might have crossed it in the past. (Such events might account for Venus's baleful reputation in to the oldest myths.)
The clouds (and presumably anything floating in them) ‘orbit’ the planet much faster than the planet rotates. It only takes about 4 days for the upper cloud decks to circle the planet.
From an energy-efficiency perspective, the difference is negligible. Getting out of the gravity well is by far the biggest hurdle. From there you might as well just give it a gentle push over to mars.
Why waste precious carbon that could be turned into life, industrial equipment, and fuel when energy from the sun is plentiful and otherwise wasted as it radiates into space?
Depends how dense the oxygen is ;) It wouldn't, but there are methods to retain it. If we had the capability, which we definitely don't, currently.
On earth we have a magnetosphere that protects our atmosphere from erosion from the deluge the sun gives us (hello Auroras!) but Mars doesn't have that. It's size is an issue too plus it's distance and orbit around the sun now. It didn't used to be so barren, it had massive lakes and oceans and possibly life once upon a time. To terraform it now would take a level of engineering that we don't have, but could, if we manage to not nullify ourselves in the next 200 years.
No, particularly in combination with the lack of an active magnetic field to shield the atmosphere from the solar wind. It's thought Mars had a much thicker atmosphere in the far past, now mostly bled off into space. Though if a new atmosphere were created, it would be lost again on a very, very long time-scale -- hundreds of millions of years. It might work to just "top up" once in a while.
It's almost 10% less. It's either a really weird coincidence or it says something interesting about planet formation that Earth, Venus, Saturn, Uranus, and Neptune all have almost the same gravity at the surface. (Of those five, Neptune has the highest gravity at 1.137g and Uranus is the least at 0.886g.)
It is also unique, among those, in being wholly unable to sustain a buoyant aerial unshielded nuclear reactor.
Titan can. But its surface gravity is less than a seventh of Earth's. It seems unlikely people can live on Titan or the Moon for long without fatal loss of skeletal tone. (Mars might be possible, but why bother?)
For those wondering, the gravity, temperature, and air pressure in the cloud tops of Venus are all near Earth-normal. And, breathing air is buoyant.
Mars is a frozen, dry dump. There is really no value in sending live people there. They would take one trot around the lander and want to go home.