Your statement is a little hard to refute because I don’t know what you’ll admit as “viable”, but here’s a recent proposal which doesn’t require the magnetosphe

Your statement is a little hard to refute because I don’t know what you’ll admit as “viable”, but here’s a recent proposal which doesn’t require the magnetosphere actually being located on Mars: https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmo... And I guarantee you that this isn’t the only proposal that has been worked out.