[Psalm 73]

"...at that tremendous distance it would take between 10,000 and 20,000 years to complete one orbit around the Sun.

So last time it may have been even remotely visible would have been 10K years ago? Thus no historical records.
What would happen if suddenly appeared off in the (astronomical) distance? Could it have an affect on the earth? (Should I look into an insurance policy that covers this type of event?)
ARE WE ALL GONNA' DIE?

[jimpick]

I dont think Al Gore has said anything about this planet so we must be safe.

[LibWhacker]

So last time it may have been even remotely visible would have been 10K years ago? Thus no historical records.

Definitely not a naked eye object. It's about the size of Neptune and 20 times further away on average. Even with telescopes, it took us over a century to spot Neptune.

It's effect on Earth? Nada, with probability 0.99999999...