Usually you'd want to scout before hopping a planet if at all possible, too. Otherwise heavy casualties and wrong-turns are really likely. And if the AI is really entrenched, then just sending through ships paired with lightning missiles (and/or ships that are not in transports) is usually the way to go. You could also use a mobile force field (mark III force field), but that's a bit more challenging and requires a lot of knowledge to unlock. If the planets in between where you are and where you want to go are too insurmountable, you could always consider a Nuke or an EMP missile, too. Just be very careful with those, and make sure the cost is worth the benefit.