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109 There is one predictable event that will require our descendants to leave their planet of origin or go extinct. In roughly 1 billion years, our expanding Sun will render the Earth inhospitable for life. The real chal- lenge, said Jill Tarter, is surviving one’s star; there may be few who do so.” Astronomers are watching another sun die, burning its planets to cinders. This expanding star, 550 light-years away, has engulfed its children. As astronomer David Neufield described it, we are witnessing the apocalypse that will destroy our own solar system. Other intelligences might someday watch the tragedy of our own extinction—if we do not build self-sustaining habitats beyond the Earth.” Mind-Stretcher. If more advanced intelligent beings saw that we were in danger of being wiped out by an astrophysical event, would they do any- thing to help? They could give us advice on how to divert an approaching celestial body, or on a more affordable way of migrating outward from our expanding Sun—if they cared. Historian Will Durant once wrote that humanity exists by geological consent, which can be withdrawn at any time.”” We may now extend that concept to say that Humankind exists by astrophysical consent. That, too, could be withdrawn at any time. A civilization-ending accident could occur unexpectedly, even within the lifetime of humans who now populate the Earth. Although most of us now attribute disasters to causes identifiable through science, violent geological events in the past such as earthquakes, erup- tions, landslides, and tsunamis often were transformed into visits by gods and monsters.”” Some humans may attribute future disasters to deities—or to powerful aliens. Neither the optimists nor the pessimists have proven their cases about how long technological civilizations live. The future of life on Earth and beyond, a question hardly enunciated in early exobiology, remains the least developed of astrobiology’s major questions.”* We have no way of knowing the longevity of alien civilizations other than by detecting them and learning something of their histories. Inserting solid numbers may have to wait until we discover evidence of a civilization older than ours, or find the remains of one that is now extinct. Strangely, the possibly disastrous impact of contact with a more techno- logically advanced civilization is almost never mentioned in this context. Many of those most pessimistic about the human future are very optimistic when they speculate about the consequences of contact with intelligent A Growing Sun A Growing Sun