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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.
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When it's finally spotted, I bet it's oblong and dead black ...
Well, this IS 2001, after all...
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unless I miss my guess, it's been some while since ol' Isaac A. has written on this subject.
[and isn't Franco still dead too?]
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Max, my understanding (again, per Asimov) is that it's believed that Jupiter itself is just about at the brink of the size above which nuclear fusion would be triggered. (There is rough evidence than Jupiter itself is a bit hotter than such an object would be if non-nuclear, thus suggesting a small amount of nuclear activity at the planet's core). And the Discover article hypothesizes an object roughly 10 times as massive as Jupiter. Raising the question: if so, why no nuclear ignition? (I ask that as a layman, of course.)
As to your point about any known planets orbiting other stars, my answer is very straightforward: I don't know. Let's see if either of us can find anything with a little LIU, as to their size and how their existence was seen or inferred.
tsuwm, granted that Asimov is dead; my point is that the article in essence provided no new science beyond what Asimov wrote some time ago.
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as Max's links will affirm, things have changed a bit since IA wrote on the subject. here's another link: http://www.nationalacademies.org/ssb/wsmoch1.htm
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tsuwm, I don't see any real changes; just the same old speculation. BTW, Max, you don't need anyone to "gist" the article; your link gives 100% of the text in the printed magazine.
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Max, I'm professing ignorance, not scepticism. No doubt extrasolar planets exist (the converse is, statistically, absurd), and I think I recall that some have been detected. I just don't recall anything more about those that were detected. (dumb ignorant -e)
But to make this a word-post: if "solar" is limited to our star, and not to stars generally, what do you call a planetary system around another star? Is there any term less cumbersome than "extrasolar system"?
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