Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:
SEDNOID
There are currently only two known sednoids. The first is Sedna (from which the word sednoid is derived). The other is named 2012 VP113 (or “Veep,” as I like to call it).
A possible third sednoid was discovered in late 2015. It has the fun, easy-to-remember name V774104. It may take a while for astronomers to determine V774104’s orbital path. It will take a bit longer for them to think up better names.
There’s a lot of ongoing debate over what exactly these two (or three) objects are. They might be former Kuiper belt objects, or they might be part of the Oort cloud, or they may even be objects captured from other star systems.
For our purposes, the defining characteristic of sednoids is that they keep their distance from the rest of the Solar System, coming no closer to the Sun than 75 AU. For the sake of comparison, Neptune orbits the Sun at a distance of approximately 30 AU, and the Kuiper belt terminates at a distance of about 50 AU.
This means sednoids are so distant that they don’t have any significant gravitational interactions with the eight known planets. As far as Sedna and Veep are aware, there may as well be no planets in the Solar System at all.
Okay, the orbits of both Sedna and Veep are a little too strange. They’re too eccentric. Way too eccentric.
At perihelion (closest approach to the Sun), Veep is approximately 80 AU away; at aphelion (farthest distance from the Sun), Veep is over 400 AU away. Sedna’s orbit is even crazier, with perihelion at 75 AU and aphelion at a distance of over 900 AU!
It’s hard to believe the sednoids ended up in these bizarre orbits on their own, so they must have had gravitational interactions with something. If the eight known planets couldn’t have influenced the sednoids, does that mean there’s another planet out there? Could the elusive and controversial Planet X be responsible for these weird orbits?
Assuming Planet X exists at all.
P.S.: I’ve been highly skeptical of the whole Planet X thing, or as it is now being called the Ninth Planet hypothesis. However, after yesterday’s post on the clustering of scattered disk objects and today’s post on sednoids, I have to admit that something odd seems to be going on beyond Neptune’s orbit.
Planet Pailly 
Given the large distances and high eccentricities, I think it’s highly plausible that they are captured objects. Are they close to each other and experiencing the same clustering seen with other objects?
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They’re clustering in about the same place as the other objects. Once V774-whatever’s orbital path is determined, if it turns out to to fit the same pattern, the Ninth Planet hypothesis will be really hard to ignore.
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