The paper ... noted that a number of large, very remote objects share a similar orbital angle. That's suspicious if you're an astronomer expecting to see a random distribution of objects. The key orbital feature is known, rather obtusely, as the “argument of perihelion.” We're not shy of complicated orbital concepts (we try to toss around the phrase "obliquity of the ecliptic" whenever possible), but this one is not very easy to explain. "The argument of perihelion is the angle at which an object comes to perihelion with respect to the ecliptic plane," Sheppard said in an e-mail. Mike Brown,...