What ever happened to Planet X?

From this column, I thought I’d put in an update on the article from this:

So, just something interesting. No hard evidence as yet, but there COULD be a Planet X (or possibly a dwarf star, if we were a binary system in the past). It might be cool if there was a large planet or star out there…imagine what weird conditions might exists (especially if it’s a dwarf star and it’s still hot).

-XT

If it were a dwarf star and still hot, wouldn’t it be emitting thermal energy, and thus visible? Given the size and proximity, it would be long since seen by IR telescopes.

If there is something out there, it is likely another ice-ball like Pluto, Sedna, Eris, etc.

Since when is Neptune about four times bigger than Earth?
Powers &8^]

I guess it would depend on how big it was. Not sure if it were small enough and ‘hot’ meant it was at a few thousand degrees (or less) if we’d necessarily see it. I’ve heard folks speculate that our system is actually part of a binary system and that it’s plausible that we have a companion star that’s really small and relatively cold and that we’d not know it, but I have no idea how realistic that is.

From this article they are talking about something quite a bit larger than Pluto, Sedna, Eris or the like though.

-XT

I think they are talking strictly about the diameter there, not volume or mass (which actually makes no sense considering they are talking about gravitational distortion).

-XT

How would they distinguish between gravitational perturbations produced by a discrete Planet X and those that are the cumulative effect of a large number of Kuiper Belt objects?

I’m not an expert, but it seems to me that the gravitational vectors would be less focused if caused by multiple objects.
Powers &8^]