you might be able to if your espionage level against that race is high enough, otherwise you can't.
I believe this is intentional so that planet defense has the edge.
I could be wrong on these points but this is how planet defense has tended to be in my games. you'll still get the "defeat likely", "victory certain" etc if you click on it. Also if you zoom in, you can at least eyeball the type/size of ships flying around the planet..
