Before I can continue the series about Kuiper Belt Objects, I have to point out that there are still many unsolved problems in the classifications and definitions of celestial objects. The International Astronomical Union (IAU) should have solved some of them already when the IAU was founded in 1919 and should have solved all of them when Pluto’s “demotion”, which was linked with the official definition of what is a planet, gave a new opportunity to tackle all open questions about categorizations in 2006.

In 1997 were some planetoids discovered. Of them sparked 1997 CS29 new disputes. It was soon found that 1997 CS29 consists of two objects, which orbit each other, which means they move around their combined barycenter in the middle between them. In 2012 were the planetoids named Sila and Nunam and given the asteroid number 79360 (the asteroid number is always given together with the official name, at discovery is given the alphanumerical combination, that is proceeded by the year of the discovery, there is sometimes more than one of these, then one of them is later chosen as the official provisional designation; apart from that are nicknames, which are temporary and never official). Already the technical term asteroid number raises questions and would better be planetoid number. The current situation is strange and inexplicable because #79360 is officially named Sila-Nunam and a binary asteroid or double asteroid system, but at the same time is Sila classified as a cubewano and Nunam as a moon and the satellite of Sila.

The situation isn’t made clearer, but becomes even more confusing, when we look at the current classifications of other binary systems. 1997 CQ29 or #58534 is officially named Logos and classified as a cubewano, although this cubewano rotates very clearly around a combined barycenter, which is formed with Logos’ “moon” Zoe. Hence it should be the system Logos-Zoe. In 2012 was 2007 TY430 (unusually late) chosen as an official provisional designation for #341520 (these numbers follow, with a few exceptions, the chronological order of the discovery of the planetoids) and in 2015 was this binary system named Mors-Somnus. It is the second system, that was officially named in the manner of a binary system. This is very important when you search on the NASA servers because you won’t find anything unless you use the official name. You can’t find Sila-Nunam under Sila or Mors-Somnus under Mors, although that works better for searching the Wikipedia. Mors-Somnus is officially a double asteroid system and a plutino, yet Somnus is also classified as a moon because Somnus is a tad smaller then Mors. Another binary “asteroid” is the cubewano Borasisi, that should together with his “moon” Pabu be called Borasisi-Pabu instead. It is already strange that the size counts for the classification as “moon”, although even the question whether a system is a binary is the question about where the center of gravity is located.

Antiope (#90) is an asteroid at the outer rim of the asteroid belt. Antiope is only peculiar in having an “asteroid moon”. This “asteroid moon” has yet only the official name S/2000 (90) 1. Antiope was discovered in 1866, but back then was neither a way to know nor any reason to expect that there are double asteroid systems. That Antiope is a double asteroid system was discovered in 2000, hence the strange name of the “asteroid moon”. Because the “asteroid moon” didn’t get anything, that would deserve to be called a name, and because the name Antiope is since decades the only name for this double asteroid system, so the name Antiope is used for the whole system or both parts of it. In order to distinguish them are they (unofficially but widely) called Antiope A and Antiope B. Both components of the Antiope system count each for itself into the 500 largest asteroids of the Asteroid Belt.

Similar to Antiope is the system of Hermes and S/2003 (69230) 1, where 69230 is of course the asteroid number of Hermes. There is hardly any interest in S/2003 (69230) 1 because it seems to be absorbing all attention that Hermes belongs into the Apollo group, also referred to as the Apollo type, and this means an asteroid, that sometimes crosses Earth’s orbit, but only in the aphelion part of it. Similar in size is Patroclus-Menoetius, that is officially named Patroclus, while Menoetius is only the “moon” of Patroclus. The “asteroid number” of Patroclus is 617. Patroclus(-Menoetius) is a Jupiter Trojan at Jupiter’s Lagrange Point L5, hence it is rather irrelevant for doing astrology. It is only worth to mention that a sextile [I first wrote trine here instead of sextile, but L4 and L5 are sixty degrees before respectively behind a planet in its orbit, the trine can be derived indirectly from the Lagrange-points] in a horoscope means a conjunction with either L4 or L5 of the celestial object. An interesting case is also the Near Earth Asteroid #65803, that was discovered in 1996, an “asteroid moon” linked to it was discovered in 2003 and hence named S/2003 (65803) 1, but because the two form a double asteroid system #65803 was named Didymos in 2004. Didymos means twin! So already this official name says that it is meant for the whole double asteroid system. Hence both parts of the double asteroid system are distinguished as Didymos A and Didymos B, where the latter is the smaller one and informally also called Didymoon.

The technical term asteroid was originally made for objects in the asteroid belt in order to distinguish them from planets. Asteroids were thought to be found only in the asteroid belt. Meanwhile seems Asteroid Belt to be nothing more than a name (hence capitalized here as opposed in the sentences, where I use it as a technical term) and asteroids to be found everywhere in the solar system. Asteroids are categorized as Inner Belt, Main Belt, Outer Belt or belonging to groups, which are named after certain asteroids. This groups consist of asteroids, that cross the orbits of planets. Most of them cross the orbits of planets, that are found closer towards the Sun than the Asteroid Belt. But this could also be because asteroids, that cross the orbits of outer planets, are also in other categories. Sometimes the groups are called types, but this is confusing because the type of an asteroid should actually describe of what material it is composed. This is related to the classification of comets because this describes meanwhile the activity of a celestial object, that can be found anywhere, and is only by this distinguished from an asteroid, although comet meant originally that the object has a wider orbit, so that it wasn’t possible to keep track of it with the telescopes of past centuries. So this means that the term asteroid has meanwhile many meanings. It can describe a celestial object by its size, its material, or its orbit. It is never clear what is meant.

There is a similar situation for transneptunian objects. So can Sedna be counted as an Inner Oort Cloud Object, or as an Outer Kuiper Belt Object, or as an Outer Scattered Disc Object, or as an Outer Detached Object, or simply (but rather unofficially) as a Sednoid (but inexplicably not as Sednaid, although Sedna would give the name to this class or group). If a celestial object crosses the orbit of Saturn and Uranus, then it is classified as a centaur. But it can cross Neptune’s orbit additionally, then it is classified as a centaur and as something else. So is Typhon (#42355) an asteroid (by size), a centaur and a scattered disc object. Typhon has an “asteroid moon” with name Echidna and is actually, but again not officially, a double asteroid system. The larger part of a double asteroid system can be called the primary and the other part the secondary, but until now this corresponds also with the chronological order of their discovery, so this could be an only temporary solution. Typhon should actually be called Typhon-Echidna. The same is true for Ceto-Phorcys, where Ceto is numbered (#65489) and classified as a Scattered Disc Object, an asteroid, and a centaur, while Phorcys is officially “only” an “asteroid moon”. Although only the binary character of this system made it possible to calculate the mass of this system directly.

A bit different is the case of Hidalgo. It is classified as an asteroid, but it is seen as likely that it is the remnant of a comet, both by size and by orbit, but Hidalgo crosses Jupiter’s orbit and touches Saturn’s orbit and that is seen as enough for also categorizing Hidalgo as a centaur. But obviously not enough people agreed with this classification for giving Hidalgo the name of a centaur instead of the name of a politician. It is very doubtful whether Hidalgo (#944) should really be a centaur, considering that Hidalgo doesn’t eventually cross Saturn’s orbit. A centaur should be in orbital resonance with Saturn as well as with Uranus!

There are lists of binary, trinary and more multiple “asteroid” systems. These lists are again trying to redefine the term binary because they list really everything, as far as known, that is orbiting something. Examples for that are Weywot, Alexhelios, and Cleoselene. Weywot is an “asteroid moon” of Quaoar. It is only special insofar as the tribe of the Tongva was asked to name it and granted the right to do so. But that’s it already. It isn’t in question that Quaoar is in the center and only Weywot orbiting it. Alexhelios with 9km diameter and Cleoselene with 7km diameter are true asteroid moons (although I dislike the expression moon for a satellite because moon is derived from the proper name Moon) of Kleopatra with 112km diameter. Kleopatra (#216) is a classical asteroid, this means a Main Belt Asteroid and big enough to have a core, a mantle, and a crust. Alexhelios and Cleoselene only orbit Kleopatra and there is no doubt about this, yet some lists want to define this as a trinary system. It isn’t wrong from a mathematical point of view, but it is confusing when such terms are also used for describing the location of the center of gravity or barycenter.

Finally Pluto should actually be named Pluto-Charon! Pluto and Charon are both orbiting around the barycenter of Pluto and Charon and Pluto’s other “asteroid moons” or satellites, how the correct technical term would be, are also orbiting the barycenter of Pluto and Charon. Already for this reason should the topic have been tackled while discussing the status or classification of Pluto in 2006.