Why we can accurately detect stars billions of light years away, but we can’t confirm if we have a 9th planet in our solar system?

Question

Why we can accurately detect stars billions of light years away, but we can’t confirm if we have a 9th planet in our solar system?

In: 2123

Answer 1

For the same reason that, at night, you can see someone with a flashlight from far away, but can’t see, say, a nearby blue bouncy ball perhaps even if you’re pointing a flashlight right at it.