Incomplete. Knowledge from other Asimov:
A further planet was hypothesized as an explanation for the irregularity in Uranus's orbit. Searching for that planet, Neptune was discovered.
A further planet was hypothesized as an explanation for the irregularity in Neptune's orbit. Searching for that planet, Pluto was discovered in the 1930's.
However, satellite probes (in the 1970's, I think) revealed that Pluto is quite small -- too small to account for the Neptune irregularities. Ever since then, it's been hypothesized that there's something else, further out. The astronomer featured in Dicover is not, in this, working on anything new and novel. Nor is he, by his own admission, anywhere near a breakthorough.
My understanding (very vague) is if that something were as far out as the Oort cloud, it would have to be extremely masssive to account for the Neptune irregularities. And that raises (to me) the further question: if it's that big, how come its gravity hasn't been great enough that the its core heat, generated by gravitational collapse, triggered nuclear fusion -- so that the body would be become a star (and thus visible), rather than a planet?
Seem unlikely to me. My conclusion is that the guy featured in the Discover article is a squirrel. Reading between the lines of the comments of other astronomers quoted in that aritcle, it appears that they share my conclusion. I notice that the featured astronomer is working on this solely "on the side"; no one's interested enough to be funding him.
