When it comes to small (-er than, say, Jupiter) bodies in the distant outer Solar system, here's one relevant piece of information: Because these bodies' light

When it comes to small (-er than, say, Jupiter) bodies in the distant outer Solar system, here's one relevant piece of information: Because these bodies' light is purely reflected solar light, whose brightness drops as the sun-object distance squared (d^2), their brightness as seen from Earth drops as the sun-object distance to the fourth power (d^4), making them incredibly faint.