The great saint Vatsyayana, in his famous Love manual, classified women according to their beauty and physical attributes. He also classified types of romantic involvement and physical intimacy. He even classified qualitatively various parts of the female anatomy according to their aesthetic appeal or reproductive advantage. Yet Vatsyayana is not alone. In general we, human beings as a race, have always had a natural tendency to classify all objects under the Sun and also all objects in the heavens. Thus, from time immemorial, Emperors, Historians, Anthropologists, Astronomers, Chemists, Botanists, Zoologists to name a few have never resisted an opportunity to classify not only objects but also people depending on their own respective specialties.
Astronomers classify stars according to their size and brightness or temperature. Zoologists classify animals according to their species or habitats or peculiar manner of evolution. Engineers classify bridges, aeroplanes, guns, in fact, anything that one can practically think of in our day to day existence. The question arises whether there is any object which defies classification. It is in this context, that one must take the case of Chiron, a stellar object discovered about four and a half decades ago.
While as we have seen most people have a natural inclination to try to classify the objects in the material world, this becomes almost an obsession in the case of astronomers, chemists, physicists and biologists who are constantly discovering or finding new objects, organisms as the case maybe in the course of their work.
But once in a while, scientists notice a freak object that can not be fitted into any known category or slot. One such freak is the mysterious object Chiron that travels in our solar system between the orbits of the two planets Uranus and Saturn. Chiron was discovered by Charles Kowal, an astronomer at Caltech (California Institute of Technology) in the United States in the year 1977. Charles Kowal has had an impressive record of discoveries. Apart from having first spotted Chiron, he is credited with the discovery of various sky objects from supernovae to satellites of other planets.
When Kowal first discovered Chiron, scientists were disturbed as well as excited. Every astronomer tried to fit Chiron into his own pigeonhole with little justification or success. Many astronomers labelled it either an asteroid or a planet or a comet. Some went so far as to speculate that it might be an escaped satellite of Saturn, Uranus or Neptune or even the member of a new species of space objects.
Forty years after the planet Uranus had been discovered by Herchell in 1781, a French astronomer noticed that the planet’s observed position did not agree with its calculated orbit. It was noticed that the planet was being pulled slightly off course i.e. “being perturbed”, as is known in astronomical parlance, by the gravitational attraction of an outer planet. This discrepancy was used by two astronomers to calculate the theoretical position of the eighth planet Neptune which was discovered finally by John Galle in 1846.
But even the mass of Neptune could not fully account for the distortion of the orbit of Uranus and so began the search for a ninth planet. But Pluto, which was discovered in 1930, was found to be 100 to 1000 times too small to account for the wobble of Uranus.
When Chiron was spotted, there was speculation as to whether it could be the tenth planet, that everyone was looking for in the skies, but it was found to be too minute and its mass too small for it to be classified as a planet.
Two Caltech astrophysicists announced in January 2015, new research that provided evidence of a giant planet tracing an unusual, elongated orbit in the outer solar system. The prediction was based on detailed mathematical modelling and computer simulations, and not on direct observation.
However another astrophysicist, in NASA opined that it was too early to say with certainty there’s a so-called Planet X on the basis of early prediction based on modelling from limited observations.
Anyway Planet X has not yet been discovered, and there is debate in the scientific community about whether it exists.
Much of this confusion regarding Chiron has arisen from the nature of Chiron itself. Because it appears rather faint, it is extremely difficult to study in detail. Nevertheless, as astronomers continued to observe it, they have begun to learn a few things. Using infrared techniques, astronomers at the Mauna Kea Observatory in Hawaii have estimated that Chiron is 300 to 400 kilometres in diameter. Its surface is dark and is believed to be covered with either dust or rocks, a makeup similar to the surface of some asteroids.
Though scientists know very little about Chiron’s physical properties, they know its orbit quite well. This is because Chiron has been photographed though perhaps unintentionally many times. However it was only in 1977 that it was noticed as a distinct object for the first time by Kowal, and photographed many times subsequently.
This long series of inadvertent observations, however, prompts us to compute the precise orbit of Chiron. Scientists now know, for example, that its period of revolution around the Sun is 50.7 years. With this information scientists can compute Chiron’s orbit back as far as the third millennium B.C. However, every few thousand years Chiron passes extremely close to Saturn. These close passes drastically affect Chiron’s orbit making it unstable. Because its present orbit is so unstable scientists feel Chiron could not possibly have remained where it is now since the birth of the solar system and that it must have come from somewhere else. This is the question that is now troubling scientists.
Though Chiron is similar in size and surface composition to some of the larger asteroids, it most probably is not one of them. Almost all of the asteroids lie in a belt between the orbits of Mars and Jupiter and even the most eccentric pass through the belt in some part of the orbit. Chiron, on the other hand, never goes anywhere near the belt. Therefore, this is an indication that it certainly originated in a different part of the solar system. Some astronomers were inclined to think that Chiron’s orbit would not be unusual for a comet. This idea, however is of little value since comets can be found almost anywhere. Furthermore, comets are typically hundred times smaller than Chiron. Even the famous Hailey’s comet which could be seen with the naked eye from the Earth is less than ten kilometres in diameter.
If, then Chiron is not related to asteroids or comets, the only other objects it resembles are some of the satellites of the planets. Chiron does, in fact, resemble Phoebe, Saturn’s outermost satellite, in both size and physical makeup. It would seem at least possible that Chiron could be an escaped satellite of Saturn itself or perhaps of Uranus or Neptune.
But, this theory cannot be readily accepted because it is not that easy to rip a satellite from its planet. It would take the powerful gravitational influence of some massive body, something on the scale of Neptune passing close by to do this. Could this body still be out there somewhere in the solar system?
Right now Chiron is still very far away from the Sun. Astronomers should in the not too distant future be able to learn much more about its physical nature and perhaps even about its origin. Until then, however, Chiron will have to sit in a pigeonhole all by itself regarded a freak of nature that defies classification.
The solar system has only eight planets, the Earth, Venus, Mars, Jupiter, Mercury and Neptune) though Chiron has erroneously been named as 2060 Chiron, a minor planet; it has also erroneously been named 95 P/Chiron as a comet, an indefensibly wrong astronomical nomenclature!
Coming to Pluto, it is now considered to be one of the largest known members of the collection of icy bodies on the outer fringes of the solar system, known as the Kuiper belt. When a body of scientists decided a formalised definition for the term “planet” in 2006, Pluto was demoted from its planetary status. That being the case astrophysicists would not be inclined to accord the status of a planet to Chiron.
As things stand now, Chiron, is neither a planet nor a comet despite some similarities with them.
It is considered as the first identified member of objects known as centaurs -Stellar bodies orbiting between the asteroid belt and the Kuiper belt and named named after the centaur Chiron in Greek mythology. Therefore until some Galileo or Kepler comes up with the right answer we would have to continue to describe it as perhaps a Planetoid or more appropriately an unclassified stellar object.