The Most Famous Asteroid...

 ...may not have been an asteroid at all. A new, very solid theory suggests that what really killed the dinosaurs was a fragment of a comet.

Comets sometimes go so close to the sun that they hit the roche limit, the point at which an object loses structural integrity due to the tidal forces and gravity of the body it's orbiting. This causes them to break up, but they keep following the orbital path. The math shows that one such fragment is very likely what hit the Earth 66 million years ago. Kind of like a big piece of shrapnel.

And it hit at the worst possible angle. The dinosaurs got very unlucky. (Or it was aliens. Nah).