NASA is planning to send people to Mars to live there - but why they don't try to live on the Moon first?
Possibly because Mars is more similar to Earth.
Going through the official NASA sites, I couldn't find a direct reason for choosing Mars over the Moon, but the Moon One site perhaps offers an insight as to why NASA might also want to go to live on Mars rather than the moon:
"After the Earth, Mars is the most habitable planet in our solar system due to several reasons: - Its soil contains water to extract - It isn’t too cold or too hot - There is enough sunlight to use solar panels - Gravity on Mars is 38% that of our Earth's, which is believed by many to be sufficient for the human body to adapt to - It has an atmosphere (albeit a thin one) that offers protection from cosmic and the Sun's radiation - The day/night rhythm is very similar to ours here on Earth: a Mars day is 24 hours, 39 minutes and 35 seconds
The only other two celestial bodies in orbits near the Earth are our Moon and Venus. There are far fewer vital resources on the Moon, and a Moon day takes a month. It also does not have an atmosphere to form a barrier against radiation."
[clip from mars one, http://www.mars-one.com , faq section]
sidenote: There are quite a few people that think we should try living on the moon first rather than mars, such as Chris Hadfield (retired astranout).
There are lots of reasons:
- The day/night cycle on The Moon is too long compared to to Earth's, while Mars has one that is similar to earth's.
- The Moon's gravity is is very low, which has been proven to cause problems in humans. Mars' gravity is still only 40% of earth's, which is little, but at least better than the moon.
- Mars has water (in the form of ice and a little vapor). So does The Moon, but in much smaller quantities.
- The Moon is exposed to solar radiation. So is Mars (as compared to Earth), but at least a little protection is offered by what little it has in the way of atmosphere (Neither the moon nor Mars have a magnetic field like earth has).
The most important reason, though, is that there simply is no reason to colonize The Moon.
We are not trying to establish permanent livable cities on mars, much like Antarctica, the humans living on Mars would be scientists, there to make new discoveries, study the only known occurrence of extraterrestrial life etc.
The moon simply does not hold much value in that regard.
Money, as usual.
There's a very good answer over on space.stackexchange
Essentially, the increased cost of having to move stuff further when going to Mars is currently offset by the lower projected cost of creating a habitable environment and currently larger potential gain when going to Mars.
However, "projected cost" and "potential gain" are quite volatile variables at this point in time.
The question is really how the calculation looks once we're ready to actually build a research settlement on the Moon/Mars. If at that time the Moon or Venus suddenly looks more attractive than Mars (including considerations like PR and funding), we'll go there instead.