It's funny how this stuff gains popular traction. "Planet X" has been theorized for years (in different variations, with different definitions, but knowing how some of Einstein's theories were "disproven" by science only to later be found correct, maybe this was exactly what Percival Lowell was referring to in the 30's), but even when it was published in semi-mainstream publications like Nature it would be in
an article like this. So I'll ask the astrophysicists I know when I see them next, but from my layman's take these CalTech guys didn't actually propose anything new, just had slightly deeper/better data, so I can't figure out why it's gaining so much traction right now. Regardless, it's still cool, and anything that inspires the public to support space (or deep sea) exploration is cool in my book.