In fact, we’d probably notice even it were covered in finely-ground coal dust; the planet Mercury is slightly less reflective than the Moon and that’s darker than coal dust. Yet it’s visible enough.
I think I’ve been whooshed.
Here’s a more detailed account of the story of Planet X.
The idea of a planet sweeping through the solar system and tossing the Earth around is, um, not terribly factual. Ain’t gonna happen. I won’t go into detail right now, but I am planning a web page on it. Until then, read this one.
Oh, I’ll be on Art Bell’s radio show on July 22nd talking about it too.
Wow, Bad Astronomer! Just recently it was Discover Magazine, now Art Bell! What’s next for you?
Seriously, keep up the good work!
Just want to point out that there is (at least) 2 planet X’s
The 1st one was a fudge factor to explain variation of the orbits of the outer planets and of no threat to us (but a good place to pick up some dilithium crystals.)
The 2nd ( the one mentioned in the OP) is more of a brown dwarf or failed star with a highly eleptical orbit (much like a comet) that plays havoc w/ the solar system as it rounds the sun.
SDMB, of course. Then. on to Master of the Universe, if I can overthrow the evil Skeletor.
Really, I have no idea. I take 'em as they come my way. But stay tuned for that Planet X page on my site. I hope to have it up after the 20th, when I get a chance.
Quoth k2dave:
The search for that first hypothetical “planet x” was the one that resulted in the discovery of Pluto. The purported variations in Neptune’s orbit, combined with Bode’s Law (which now seems to have just been a coincidence) predicted the location of the planet, and by pure luck, Pluto happened to be in that particular part of the sky at that moment. Two things came to light shortly afterwards, though: First, Pluto is far too small to have produced the observed effects on Neptune, and second, the observed effects turned out to have just been experimental error in the first place.
Those who heard about that first minor detail, but not about the second, figured that X was still out there to be found, and because that’s not all that dramatic a story, some versions started throwing in the global catastrophe angle.
Good work, BA. Ironically the reason I searched this is because over the past month, it seems every single crackpot “prophet” Coast to Coast has on is predicting Planet X “passing through the solar system” and immediately my Bullshit meter went to 11 each time.
Even if there WAS a Planet X by Pluto, wouldn’t it take decades to pass by earth? I don’t think people have any clue how truly large the Solar System really is.
Yeah, I’m terrified of those Planet Xian,I hope they never make it here. How would Bush handle that one?? 
They are still searching for planet X. Someone here posted that the planet X search resulted in the location of pluto. This is correct. But all of the planets in the solar system have unexplained perturbations in their orbits. Hence, scientist assume that there is another planet causeing this phenomenon. So the search for planet X is still going on.
Ok, enough of that BS, if planet X ever threatens us, the council of worlds will intervene. Earth is a galactic game preserve for mosquitos, which are extinct everywhere else, and the coucil of worlds will not let a disaster such as collision by a planet to risk the destruction of these precious little gems of life.
In other news, people finally agreed that “Planet X” is a term being to describe 15,000 different concepts in the past 100 years, so everyone is talking about something else. And The Bad Astronomer f*ing rules.
Planet X is not to be confused with Counter Earth, a planet exactly the size and makeup of our on, which revolves around the Sun exactly opposite our Earth, so that we can never see it.
On Counter Earth, life and civilization have evolved exactly as they have here, so that the odds are good that each of us has an exact duplicate living there, probaby making the same mistakes and posting on the Counter Earth Message Board right now.
Ive always wondered how, if this duplicate planet was always on the other side of the sun, that anyone knew about it in the first place, but thats just another of the persistent mysteries of life…
First off, Zagadka, kewl name, my Big Brother. 
Second, there is a lot of confusion about Planet X, mostly spurred on by either the confusion of the people promoting the iodea, or their outright falsehoods. For example, a lot of them are hazy on whether the magnetic poles of the Earth flip, or the rotation axis. Some conflate the two, mixing and matching them. It’s amazing.
I have my webpage up about it: Planet X silliness revealed. I am still working on it, and will add stuff in the next couple of weeks, I hope.
Isn’t that Bizarro Earth?
Besides, if a planet was heading towards Earth, we would just have to send a space shuttle to it, drill 800 feet into the crust and detonate a nuclear bomb. That should do the trick.
Planet XI, of course, the twin to Planet X.
Yes, you’d better shield yourself from all that gravity… 
Plus, on Counter Earth (where there is no war or hunger or traffic accidents), there are these two Japanese women who eat children and control a monster with a head like a steak knife and ninja stars inside. We are doomed–UNLESS GAMERA CAN STOP THEM! HELP US, GAMERA!
Just for kicks, I did the math using the info I could find on Nibiru (passing within 14 mil. miles, 25x Earth’s mass). It would produce an aberrant acceleration of the Earth of less than .01 mm/sec/sec. Ooh, now there’s something to worry about… shakes head
Actually, Planet X is going to make the Earth start spinning backwards, thereby reversing the flow of time.
Where is BZ0000 when we need him?!