I believe solar would work, but it would just take longer. EDL for a substantial payload to Mars hasn't been done before, but there's no reason to think it's a

I believe solar would work, but it would just take longer. EDL for a substantial payload to Mars hasn't been done before, but there's no reason to think it's a show-stopper. A lot of the engineering challenges for that are the same as the engineering challenges for returning the first-stage to Earth, like supersonic retrorockets.