[Cincinatus]

IMNSHO, Nuclear is the only way to go. The advantages far outweigh the risks.

It's not really a risk issue -- it's cost. Using an RTG pushes the total mission cost up by at least several tens of millions of dollars. We already know we can operate successfully using solar power on Mars; why not use what works and is cheap?

[cripplecreek]

We know that solar works well in well lighted areas of mars but what about areas that don't catch as much sunlight? I'm thinking of canyons and polar regions. Also this will be a much larger lander requiring a lot more power.

[Yo-Yo]

Solar works for a short time. Solar cells on both Spirit and Opportunity have steadily degraded as fine dust covers the collectors. Batteries must be used to store energy during the daytime for use at night and in shadow. Battery efficiency dwindles over time with each subsequent charge/discharge cycle.

For short term missions, Solar is the only way to go. If you want to maximize reliability over the long term, Nuclear is your best choice.

[chimera]

We already know we can operate successfully using solar power on Mars; why not use what works and is cheap?

Cheaper doesn't always mean better. You'd be better to maximize the (scientific) return on your dollar invested by spending a little more to assure reliability and enhance capabilities (i.e., being able to go where you couldn't otherwise go, like polar regions and/or canyons and deeper craters, where there may be evidence of water).