= Mars =

 * Pro:  Because it's there.
 * Con:  Very little there.
 * Con:  Hellishly expensive to get there.
 * Con:  Nothing leaves (so far).
 
||<-5>  '''Very Little There'''                          ||
||                 || units || Earth  ||   Mars || Ratio ||
|| Distance  (avg) || AU    || 1.0    ||   1.52 || 1.52  ||
|| diameter  (avg) || km    || 6371   ||   3290 || 0.52  ||
||<-5> ''Resources''                                     ||
|| atmosphere mass || kg    || 5.2e18 || 2.5e16 || 0.005 ||
|| water mass      || kg    || 1.4e21 ||   5e18 || 0.004 ||
|| gravity         || gee   || 1.0    ||   0.38 ||  0.38 ||
|| cosmic rays     || rem/y || 0.03  || 10 to 20 || 500  ||
||<-2>lethal perchlorates || not yet  || yes    || ~+∞+~ ||
||<-4>total insolation (diameter/distance)^2    || 0.12  ||
||<-5>''note: Mars "water" mass may be smectite clay''   ||

Phobos and Deimos are zero for the ratios, but 6 to 8 km/s easier to visit then return.  3 meters of local regolith shielding can easily be supported by a 6 psi (50/50 oxygen/helium ) balloon containing a 1 gee rotating habitat.