You may have read today's article in New Scientist about NASA possibly scrapping plans to go back to the Moon. As the article says:
NASA will probably not build an outpost on the moonMovie Camera as originally planned, the agency's acting administrator, Chris Scolese, told lawmakers on Wednesday. His comments also hinted that the agency is open to putting more emphasis on human missions to destinations like Mars or a near-Earth asteroid.
NASA has been working towards returning astronauts to the moon by 2020 and building a permanent base there. But some space analysts and advocacy groups like the Planetary Society have urged the agency to cancel plans for a permanent moon base, carry out shorter moon missions instead, and focus on getting astronauts to Mars.
However, there's one other destination not mentioned there that would be just as worthwhile but much easier to explore than Mars.
It's the planet (dwarf planet, planetoid, whatever) called Ceres, located in between Mars and Jupiter. I've been a proponent of putting Ceres on the map as a destination for colonization for a while and have written a fairly long explanation here on my blog (yes, I know the calculations made for the rocket images are far, far too simple - they're just there to make a point), and here's a quick and very simple summary of the facts contained there.
First of all, in terms of resources there really isn't much to do on the Moon and it's not really bad news that NASA might decide not to go there. The only real advantage the Moon has is location.
Now on to Ceres:
Ceres is 950 km in diameter, giving it a surface area equivalent to Alaska plus Texas plus California - plenty to explore.
Ceres contains more fresh water than the total fresh water on the Earth, which is a huge plus. Take a look at the interior here.
Ceres has a gravity only 3% that of the Earth. It may be true that humans need full gravity to live somewhere in the long term, but if this is true then Mars is out of the question too. Ceres' much smaller gravity means an escape velocity ten times less than that of Mars, and since you have to bring the return vehicle with you when launching from Earth in the first place, that means much much less mass when launching from Earth in the first place, which saves a LOT of money.
Launch windows: yes, Ceres is farther away than Mars, but in fact it's easier to get to more often than Mars because Mars has the most infrequent launch windows of any major object in the Solar System. You have to wait 780 days for a single launch window to Mars, but only 466 days to Ceres. Since it's somewhat farther that means that the journey will take a few more months, but a journey to Mars already takes at least six months so we're talking about months in space in any case, until we have more advanced propulsive technology to our name (something like VASIMR).
To understand why launch windows to Mars are so infrequent compared to Ceres, see this video.
Weather: Mars has weird weather with dust storms blanketing the planet and making it hard to collect electricity. It also has seasons like those on Earth - a winter with less sun and a summer with more. Ceres has a short 9-hour day (that means less night to get through before the Sun rises and you can collect electricity again), no weather to worry about, and almost no seasonal variation.
Finally, terraforming. The answer to this is simple: we're so far away from being able to terraform anything that it's not even worth considering at the moment. We can barely manage to keep a station in LEO. Trust me, by the time we've reached a point that we can start actually thinking about terraforming we'll have long since achieved the ability to get to destinations close to the Earth with ease.
The first step is the probe Dawn, which is on its way now and will be at Ceres in 2015. A Ceres lander later on is being considered by NASA as well. When 2015 comes around we'll have the first close-up images of Ceres and hopefully the excitement about this new destination up close will be enough to put Ceres on the map as a possible destination for colonization, but until then (barring any extra observations before then) this is about the most detailed image we have.
Finally, I respect that many will still prefer Mars, LEO, the Moon or perhaps another destination since no destination is perfect and completely trumps the others, but we should at least keep in mind that there's no reason why Ceres should not be another serious possibility if we're actually considering sending humans out as far as Mars.