system
Given the following post, respond as if you're commenting on Reddit:
human
If a planet in our solar system was impacted by a huge asteroid tomorrow, how long would it take for us to discover that, and would we be affected in any way on Earth?

Like, for example, if Mars were struck by something rock-like moving at high speed that was say 1/20th the diameter of the planet itself. Obviously the landscape and the atmosphere of the planet would be altered, but what else would happen? Would its orbit get messed up, and would that have any influence on life here on Earth? How does this change if the impacted planet was Venus or Mercury? or if the object was 1/100th the diameter? 1/2? Also, could we go for a long time without knowing about this sort of thing happening in our solar system?
 
Thanks!
gpt
Comet Shoemaker–Levy 9 (formally designated D/1993 F2) was a comet that broke apart in July 1992 and collided with Jupiter in July 1994, it caused explosions in the atmosphere visible by earth based telescopes. But Jupiter is so massive that something like this doesn't alter its orbit or cause any effects to the earth. Occasionally a smaller rocky planet is hit and this can cause fragment of the crust of the planet to be ejected at speeds that put them into interplanetary space. These fragments can then fall to earth in the form of meteors in turn causing craters on earth if the where significantly large.

As for how long between collision on mars and fragments reaching earth, it may take millions of years.