no, I was serious. at nearly the speed of light you just need a cutter and not an asteroid to end all life on a planet. heck you could probably just strap an FSD on a soccer ball
the asteroid we associate with dinosaur extinction was probably moving ~0.0001c
as the speed of any object with non zero mass approaches the speed of light, its energy will increase without bound. it's not even really an object anymore
so at a speed like .99999c, something very small could end all life on a planet, and an asteroid would probably turn the entire surface into magma and/or significantly change the planet's orbit
Hmmmm. Golf-balls of mass destruction!