A comet grazes a planet at a distance R. Show that the planet's tidal force can disrupt the comet is the planet's mean density is greater than that of the comet. P--------R-------C F=-GMm/r2 Now my TA advises me to expand this function about r=R using a taylor series. But c'mon, this is an introductory astronomy class. We're not supposed to know Taylor series! But even if I do, I get: F_g=-GMm/R2+2GMm/R3(dr) dr=dist from center of comet m=mass of comet M=mass of planet /\ |____ Is this even right? Then I show that F_t>F_sg where F_t=? F_sg=self gravity=? I'm so utterly confused. Please feel free to include a lecture on tidal forces and taylor series! Whatever help you can give would be great! Thanks.