If you like to entertain some really interesting ideas, here's one.

Tunguska explosion in 1908 was, undoubtedly and beyond a shadow of a doubt, a nuclear explosion... almost half a century before the first nuclear weapon was made.

People have entertained all kinds of theories as to what the source of that explosion could've been, from an asteroid rich in radioactive elements to a malfunctioning alien spaceship.

But...

How about this theory: It was a nuclear ordinance that had been fired (and missed its target) in some alien interstellar war 10,000 years ago?

Remember Sir Isaac Newton?


[link to www.youtube.com (secure)]

Heck, it didn't even have to be an interstellar war.

A human-made ICBM that failed to return to Earth, and instead flew right off into empty space, could hit some inhabited planet (and, possibly, wipe out a whole budding alien civilization) on the other side of the galaxy in 1,000,000 years.

Now, here's the actually interesting part of this idea: What if we're living right smack in the middle of a galactic war zone (of countless alien wars stretching millions of years back), with bullets flying right over our heads... and we're acting like completely oblivious morons taking a casual stroll through a literal mine field of all the (long-forgotten) alien ordinance (some of which may actually be loitering munition with no expiry date) that has ever missed their intended targets?

... which is why you just don't fly a thinly-armored tin bucket in outer space.