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<blockquote data-quote="Umbran" data-source="post: 2525019" data-attributes="member: 177">Well, an impact that large releases a heack of a lot of energy.&nbsp; Some of that energy goes into ejecting mass (which would later become the Moon).&nbsp; But a lot of it has nowhere else to go, so it just goes to heating things up.&nbsp; Melt the surface enough, and it just flows and the whole thing becomes a sphere again, and you never know it happened.However, you'd certainly notice it all less if it happened over 3 billion years ago, instead of less than one billion years ago.Depends upon the star.&nbsp; The bigger the star, the faster it burns.&nbsp; Some stars only live several billion years.&nbsp; And it isn't &quot;fade or supernova&quot;.&nbsp; For one thing, the fade is preceded by an immense brightening - the thing swells into a red giant before fading.&nbsp; And, for another, between fade and supernova lies the more mundane, ordinary nova.We can't predict the minute details - like exactly when a given star will die.&nbsp; But, many of the generalities are figured out on somewhat more than a &quot;educated guess based upon conjecture&quot; basis.&nbsp; The reactions that make the star burn are more than conjecture.&nbsp; The effects of gravity are more than conjecture.&nbsp; The two get together, and make the lifespan of a star.&nbsp; And it isn't like we don't have observational data.&nbsp; There's an entire universe we get to look at, and see if our theories predict what we'll find.</blockquote>

[QUOTE="Umbran, post: 2525019, member: 177"] Well, an impact that large releases a heack of a lot of energy. Some of that energy goes into ejecting mass (which would later become the Moon). But a lot of it has nowhere else to go, so it just goes to heating things up. Melt the surface enough, and it just flows and the whole thing becomes a sphere again, and you never know it happened. However, you'd certainly notice it all less if it happened over 3 billion years ago, instead of less than one billion years ago. Depends upon the star. The bigger the star, the faster it burns. Some stars only live several billion years. And it isn't "fade or supernova". For one thing, the fade is preceded by an immense brightening - the thing swells into a red giant before fading. And, for another, between fade and supernova lies the more mundane, ordinary nova. We can't predict the minute details - like exactly when a given star will die. But, many of the generalities are figured out on somewhat more than a "educated guess based upon conjecture" basis. The reactions that make the star burn are more than conjecture. The effects of gravity are more than conjecture. The two get together, and make the lifespan of a star. And it isn't like we don't have observational data. There's an entire universe we get to look at, and see if our theories predict what we'll find. [/QUOTE]

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