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© by Zane B. Stein

I-A. WHAT IS CHIRON?

A. Astronomy

Chiron was the first discovered of a brand new type of body, termed Centaurs by astronomers. There are now at least FORTY ONE all together. Pholus was next named, and then Nessus. Read all about these bodies, and others, below.

The following is taken from my lecture, The Meaning of Chiron, given Dec. 16, 1979 for the Astrologers' Guild of America.

"1977 was a big year for astronomers, with many discoveries altering our conceptions of the solar system. In March, for example, rings were found around Uranus. This meant that Saturn had lost its monopoly on rings, but it also meant that Uranus and Saturn had something in common.

"It was an especially big year for one astronomer in particular named Charles T. Kowal. He started off the year discovering a comet and an asteroid, and rediscovering two bodies that had been lost. But the biggest discovery of all took place that fall."

On November 1st, while studying photographic plates made on the nights of Oct. 18 & 19, "he spotted an object on the photos inside the orbit of Uranus. This was Object Kowal, which he soon named Chiron."

At first, the newspapers had a field day, announcing that the tenth planet had been found! Soon, though, astronomers with cooler heads declared Chiron to be a 'minor planet', and thus grouped it with bodies like Ceres, Eros and Hidalgo. (It soon became apparent, however, that Chiron was quite different than other minor planets. For example, photos of Chiron near aphelion in 1970 revealed that, even at that great distance from the Sun (near to Uranus) it was very, very bright.)

When Chiron reaches its perihelion, it is actually closer to the Sun than Saturn ever gets, and at aphelion Chiron reaches almost to Uranus' orbit.

In the late 80's, there was evidence of a coma around Chiron, similar to that of a comet. Over the next several years, the evidence mounted until it was overwhelming....Chiron was a comet! But a very unusual comet....it is over 50,000 times the volume of a typical comet, which makes it about the size of an asteroid! So, the debate began. Comet or Asteroid, which is Chiron?

This discussion was further fanned in 1991 --- a body was discovered that confused the asteroid/comet issue even further. (The exact time of the discovery is not known, but here is a quote from one of the astronomers who was involved, Robert McNaught: "The time of exposure was 1991 Feb 18.52973 UT to 18.57140 UT and the object was discovered on that plate perhaps 20 hours later when I scanned it. The observer was P. McKenzie. Confirmation was by myself....on 1991 Feb 19.67361 UT." The telescope was at the Anglo-Australian Observatory, Siding Spring, NSW, Australia.)
Named Damocles, it is quite unique in many different ways. Scientists don't know exactly what it is as yet. It may be an asteroid, or the nucleus of a dead comet, or something new. For now, they are calling it an "asteroid-like body." But its orbit bears a closer resemblance to a comet. When it is furthest from the Sun (aphelion), it reaches 22 AU (beyond the orbit of Uranus...no body resembling an asteroid had ever been found out that far.) And when it is closest to the Sun (perihelion), it is only 1.6 AU, which means it crosses the orbit of Mars. This body's orbit is more eccentric than any planet or asteroid currently used in astrology, with an eccentricity of about .866902. If you consider that a circle is 0, and a line 1, you can better visualize this. By comparison, Venus, the least eccentric, has an eccentricity of .006774, and fairly eccentric Chiron is .3847424. Due to this eccentricity, Damocles' whole orbit only takes 41.01 years! Contrast that with Uran! us which is almost 84 years.

This debate became even fiercer on January 9, 1992, when astronomer David L. Rabinowitz discovered something unusual while looking through the telescope at an Observatory in Arizona. (In response to my inquiry, he wrote "I discovered it 1992 Jan. 9 at 09:01 Universal Time, about 2 O'Clock in the moring at Kitt Peak in Arizona.") In the orbital range of Saturn, he found a body that was totally unexpected. Nothing else aside from Chiron was supposed to be there. Second, this body was so unique, they had no idea how to classify it. Officially, they called it 1992 AD, but soon it acquired the nickname, "Son of Chiron". Eventually, it was given minor planet #5145. And David (since the discoverer has the right) chose the name "Pholus," he says, "after the brother of Chiron".

What are some of the strange qualities Pholus possesses? First of all, it is extremely red...more red than any known comet or asteroid. Most likely this is a layer of organic material. This is very important, so we will return to it in a moment (or you can skip ahead to read more about it now by clicking here----> RED.

Second, it orbits the sun in 92.26 years, making it the most distant minor planet when discovered, and one with an extremely eccentric orbit. In fact, it swings between the orbits of Saturn and Neptune, which is much more extreme than Chiron (Chiron's orbit is close to 51 years, between Saturn & Uranus.) The eccentricity is 0.5744593. Third, in spite of a comet-like orbit, it has exhibited NO coma or tail like a comet, even at perihelion. Could it be a used-up comet nucleus? Or a whole new type of body?

So now, Chiron was no longer alone.

But the astronomers were not through yet. At 11:45 PM on April 25, 1993 (or Apr. 26 at 6 hr 45 min UT), David discovered yet another body while working at Kitt Peak. This one was originally termed 1993 HA2, designated minor planet #7066....and then named Nessus. Nessus has an orbit of about 123.2 years, and an eccentricity of about 0.523 (I don't have the data to as many decimal places as the others, as yet.) At perihelion it is located in between the orbits of Saturn and Uranus, while at aphelion it almost reaches the orbit of Pluto.

Within months after, other bodies of like nature were found. As of February 2017, there are 97 bodies in the Centaur catagory. (This is their official designation: Centaur.).

Eighteen of these have been given names so far:

Amycus (55576)
Asbolus (8405)
Bienor (54598)
Chariklo (10199)
Chiron (2060)
Crantor (83982)
Cyllarus (52975)
Echeclus (60558)
Elatus (31824)
Hidalgo (944)
Hylonome (10370)
Nessus (7066)
Okyrhoe (52872)
Orius (330836)
Pelion (49036)
Pholus (5145)
Rhiphonos (346889)
Thereus (32532).
And Pylenor has been named unofficially, so I'll include that here as well. Chiron, however, still maintains a unique status among this group.

So, what are they...comets, or minor planets?

To resolve this, I wrote to the expert on the subject, Dr. Brian G. Marsden, Director, IAU Minor Planet Center. I knew HE would know the answer. He replied,

  • "Chiron, originally given the very temporary title "Slow-Moving Object Kowal", was given the provisional minor planet designation 1977 UB. Later it was given the permanent minor planet number and name (2060) Chiron. All along, there were discussions it might be a comet, and definite cometary activity was noticed, at least some of the time, beginning around 1988. The change in the comet-designation system introduced at the beginning of 1995 (and applicable in retrospect), allowed us to modify the provisional designation to P/1977 UB, P/ indicating that it is a short-period comet. This set the scene for giving it a permanent short-period comet number, 95P, which can be combined with the name to give 95P/Chiron. This is probably what it is best called. However, since it WAS previously given a PERMANENT minor-planet number, it ALSO retains the number (2060). So the object is permanently classified as BOTH a comet and a minor planet. There is really no conflict with this. For astrometric purposes and most orbital purposes we continue to call it (2060) Chiron and classify it with the minor planets. For some orbital purposes it can also be 95P/Chiron. For physical purposes the observer can choose which he or she feels is more appropriate. Pholus and the other centaurs have not shown cometary behavior, so they remain only in the minor-planet category. "
  • So, while the other bodies are deemed minor planets, Chiron is rare in the solar system as being both comet and minor planet!

    The Small Bodies Names Committee says there are only three bodies which are on both such lists, comet and minor planet, and Chiron is still unique even so. On their site, Cross Listed Objects, they write that Chiron was first thought to be an asteroid, and later was discovered to have cometary activity. On the other hand, "It can also happen that a comet and an asteroid, previously thought to be different objects, are identified through orbital analysis as the same object." The two bodies that are in this category are:

    What Is A Comet?

    You probably know that a comet is like a dirty snowball of various frozen gases, such as methane or ammonia, and water. But it may interest you to know how a comet may be formed.

    Imagine in some distant past, far out beyond Pluto, there is a tiny grain of dust. The temperatures out there are unbelievably cold, and because of that, any molecule that happens to bump into the grain of dust, such as a molecule of water, will stick. As millions of years pass, through one molecule or another hitting it, this grows, and a crystal lattice is formed. All sorts of molecules are trapped in the lattice, which is kind of like a hexagonal cage. Here, a bit of Methane. There, a bit of Hydrogen Cyanaide. And it grows larger, and larger.

    The technical name for this type of water ice lattice, where a trapped molecule is imprisoned, yet not chemnically combined with the ice, is a CLATHRATE. A more familiar word, possibly, is MATRIX, which is a substance (such as a crystal) in which another substance (such as a fossil) is embedded.

    The following is from "Comet" by Carl Sagan and Ann Druyan, copyright 1985, Random House, Inc.:

    "If we look closely at such a lattice, we would notice that the constituent atoms are not stationary, but instead are vibrating and throbbing in place. If we decreased the temperature, the throbbing would moderate; if we increased the temperature, the throbbing would become more violent......At a certain temperature the constituent atoms are throbbing so violently that some of the bonds become broken and a small piece of crystal lattice - an isolated water molecule - detaches itself from its fellows and goes tumbling off....At high enough temperatures the throbbing motion becomes so violent that the upper layers of ice become disengaged and large numbers of individual molecules go gushing off."

    These molecules, on a comet, go off into space.....they change from ice to vapor without ever going through the liquid state. And this is the coma, and then the tail, of the comet. Because different chemicals have different melting points, different ices vaporize at different temperatures. Again, from "Comet":

    "As the comet crosses the orbit of Neptune, a patch of pure methane ice is feebly warmed by the approach of the approaching Sun; as chemical bonds are broken, a puff of methane gas is lost into space. A patch of ammonia ice would be lost as the comet crossed the orbit of Saturn. Carbon dioxide ice would begin vaporizing in earnest somewhere between the orbits of Saturn and Jupiter."

    However, Chiron is a bit unusual, compared to a typical comet. Chiron's diameter is estimated at being between 148 to 208 km...as I mentioned earlier, over 50,000 times the volume of a typical comet. This means Chiron has a much greater gravity than a regular comet. What does this high gravity mean?

    Dr. James L. Elliot, a planetary scientist at the Mass. Institute of Technology, says that Chiron "is the only known comet large enough for gravity to hold dust in bound orbits for periods ranging from tens of days to a year." In other words, Chiron frequently has a dust atmosphere in the inner 1200 km of the coma. And this creates a strange set of circumstances: some of the gas never leaves Chiron....rather, when Chiron heads back away from the Sun, part of the gases refreeze and drop back down to the surface again! Yet, in spite of this, the coma's diameter has been measured to reach almost 2 million km!

    And there are still more unusual things about this unique comet. A team of astronomers found pictures of Chiron on older photographic plates taken 1969-1972 (pre-discovery), and found that Chiron was brighter back then than it has been since. Yet at that time, Chiron was around its aphelion...it's FURTHEST from the Sun! This is NOT the time one would expect a comet, or any type of body, to be at its brightest.

    Here is a bit more astronomical info on Chiron:

    Chiron has a very elliptical orbit, 50.7 years. This takes it from a perihelion (closest to the Sun) of 8.46 AU to an aphelion (furthest from the Sun) of about 19 AU. This means several very interesting things.

    First, it actually crosses Saturn's orbit and gets closer to us than Saturn can ever get, (Saturn at perihelion is 9.54 AU.) It crossed that line, bringing it closer to us than Saturn, around Jan. 1992! (Remember...that was when Pholus was found.) And, it once again moved out further than Saturn in January 1999....about a month before Pluto once again moves out past Neptune.

    Second, it gets almost as far out as Uranus' mean distance (19.19126393 AU.)

    Third....when Uranus is at perihelion, Chiron can actually be further from us than Uranus! On September 16, 1965, Chiron reached 18,284 AU and crossed Uranus' orbit. From then until March 13, 1975, (when Chiron again crossed Uranus' orbit at 18,469 AU), Chiron was further away from us than Uranus. (Thank you Robert for those date calculations.) Uranus was near its perihelion at that time.....the exact perihelion was in May 1966, at 18,254 AU.

    Speaking of perihelions, Chiron, recently reached perihelion, on February 14, 1996.

    ESCAPEES?

    Chiron and the other Centaurs may all have escaped from something called the Kuiper Belt, a disk of objects orbiting beyond Neptune. Pholus, especially, fits the nature of a large group of such Kuiper Belt objects. According to a recent report, there are two classes of objects there, and one of these contains objects that are said to be "the reddest objects of the Solar System".

    The report, entitled THE ASTONISHING REDNESS OF KUIPER-BELT OBJECTS, theorizes that these bodies could be an "indirect indication of extraterrestrial microbiology in the outer solar system." Possibly, there is some type of biological activity occurring on these objects even in the unbelievably cold Kuiper Belt!

    Our Chiron is not the first solar system object to be named Chiron, by the way. According to Paul Schlyter, "In April 1861, Hermann Goldschmidt announced the discovery of a nineth moon of Saturn, which orbited the planet between Titan and Hyperion. He named that moon Chiron. However, the discovery was never confirmed -- no one ever saw this satellite "Chiron" again."

    That "Chiron" may never be found, because it may not have truly been a satellite. And 37 years later, when they actually did verify a ninth moon orbiting Saturn, it was called "Phoebe", not Chiron.


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