[tjmc]

Mars has no magnetosphere which makes it a non-starter due to radiation unless you live underground or in heavily shielded dwellings.

If you have to do that you might as well start at either the Moon or my personal favourite Europa - a vast ocean of water kept warm by tidal forces underneath a thick protective crust of ice. Power would be a challenge, but there might be a way to harness either those tidal forces or the radiation from Jupiter.

[adastra]

Mars is a non-starter? I think you've received some bad information.

Average radiation on the Mars surface is 10-20 rem/year. With a thicker atmosphere it will be less. And for people spending 12-15 hours a day indoors in shielded dwellings it will be a lot less. It's not a showstopper at all.

[mixmastamyk]

The low gravity may not be enough to hold a thick atmosphere, no?

[jswhitten]

Not for more than 100 million years or so. But then, Earth will also become uninhabitable within the next few hundred million years.

[rosser]

If you want to colonize Europa, you'll have to dig a lot deeper than on Mars or the moon. Cosmic ray dosage on the lunar surface is around 30 rem/year. On Mars, it averages 50.

On Europa, it's around 500-600 rem per day. That's a fatal dose.

[tjmc]

Indeed it is. Colonizing the surface of Europa would be madness without serious shielding. What's the dose under a 200m thick ice sheet though?