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.
