Your hypothetical example is interesting because I'd come to the opposite conclusion. If we knew now that the solar system would become inhospitably to human li

Your hypothetical example is interesting because I'd come to the opposite conclusion. If we knew now that the solar system would become inhospitably to human life in, say, 500 years, no person alive now would be directly affected. But I think we'd absolutely have a moral obligation to start spending resources now to prevent harm from our descendants. Isn't this almost a sci-fi trope? I think it's hypothetical, either because while we know that the solar system has a finite lifetime, the time spans involved are absurdly long -- billions of years --, or because there are many more imminent problems that need solving (which, I suppose, is also related to the large time spans, which makes the solar system's death rather non-imminent).