Tangential speed is the linear speed of something moving along a circular path. So for a satellite the tangential speed of the satellite is just right so that gravity only has the effect of changing the direction of travel. So now can we compare this satellite to the Earth? Since the Earth has some initial momentum - it is moving in a direction,which is perpendicular to the direction of the Sun from the Earth. So that means both the satellite and the Earth have (Initial) momentum that prevents them from getting close to the Sun or Earth (In case of satellite).