Renowned string theorist proposes new way to hunt our solar system's mysterious 'Planet 9'

Interesting idea about planet hunting for #9 here. What I note is from the arxiv report, "The clustering of orbits for a group of extreme trans-Neptunian objects suggests the existence of an unseen planet of mass M ∼ 5 − 10M⊕, so-called Planet 9, at a distance of ∼ 400 − 800 AU from the Sun"

I checked this site for exoplanets, 4265 confirmed,
Okay, I hit the button too soon :). There are 107 exoplanets with masses in the range of 5 to 10 earth masses, they are all very close to their host stars. Semimajor axis 0.0116 a.u. out to 3.94 a.u. Looking for a similar sized object in our solar system some 400 to 800 a.u. from the Sun is very intriguing when compared to the known exoplanets documented now in this mass range.