Well, we can see most of the other planets pretty easily...

Five planets in our solar system are easily observed without a telescope: Mercury, Venus, Mars, Jupiter and Saturn. Uranus is just barely visible for those with excellent eyesight under dark-sky conditions, provided you know where to look.

They happen to be the brightest objects in the sky, next to the moon and sun of course.

The day we see planet 9 with the naked eye, itll be easy to know we are fucked.