Short answers, pulled from the story.
Astronomers define a sednoid as any body with a perihelion greater than 50 AU and a semi-major axis over 700 AU. This classification applies to objects like 2013 RF98 and 2014 FE72 but excludes others with similar parameters that still experience gradual migration.
Sedna remains the largest and most famous of the four known sednoids discovered so far, having been identified in 2003. It possesses an orbital period spanning approximately 11,400 years and serves as the eponymous first member of this group.
Four confirmed sednoids maintain perihelion distances far beyond Neptune's gravitational influence and share similar orientations in their arguments of perihelion near 0 degrees. These bodies include Sedna, Leleākūhonua, 2013 RF98, and 2014 FE72.
The current elliptical orbits of sednoids cannot be explained by standard gravitational models involving giant planets or galactic tides alone. Scientists analyze these paths to determine if nearby stellar passages, capture from passing stars, or a hypothetical Planet Nine caused such configurations.
Sheppard and colleagues concluded after Leleākūhonua's discovery that millions of Inner Oort Cloud objects probably exist with a population of approximately 2 million objects larger than 40 kilometers. Total mass estimates fall within ranges comparable to Pluto itself and exceed several times the combined mass of the asteroid belt.