Kuiper Belt Objects: solution to short-period comets?
Have recent ‘Kuiper Belt’ discoveries solved the evolutionary/long-age dilemma?
Recently, astronomers have discovered that several KBOs (‘Kuiper Belt Objects’) are binary—they consist of two co-orbiting masses. What are the implications for Creation?
Comets—icy masses that orbit the sun in elliptical paths—are one of many evidences that the solar system is much younger than billions of years. Every time a comet passes near the sun, it loses some of its icy material to evaporation. This stream of lost material is what gives rise to the characteristic comet tail. A comet can only survive a certain number of orbits before it runs out of material completely.1 If the solar system were billions of years old, there should be no comets left. This is explained in detail in Dr Danny Faulkner’s article Comets and the Age of the Solar System.
Evolutionary astronomers, who assume the solar system is billions of years old, must propose a ‘source’ that will supply new comets as old ones are destroyed. The Kuiper Belt2 is one such proposed source for short-period comets (comets that take less than 200 years to orbit the sun). The Kuiper belt is a hypothetical massive flattened disc of billions of icy planetesimals supposedly left over from the formation of the solar system. (The other proposed source is the Oort Cloud,3 which we have already addressed—see More problems for the Oort cloud.)
These planetesimals are assumed to exist in (roughly) circular orbits in the outer regions of the solar system—beyond Neptune (extending from 30 AU4 out to around 100 AU). It is thought that these objects are occasionally disturbed by gravitational interactions and are sent hurtling into the inner solar system to become short-period comets. In this fashion, new comets supposedly are injected into the inner solar system as old ones are depleted.
Astronomers have detected a number of small objects beyond the orbit of Neptune. The term ‘Kuiper Belt Object’ (KBO) is being applied to these objects. The first of these5 was discovered in 1992, and many more have now been detected. What are we to make of these discoveries? Do these objects confirm the existence of a ‘Kuiper Belt’ as the evolutionists were expecting?
There is no reason to expect that the solar system would end abruptly at Pluto’s orbit, or that minor planets could not exist beyond the orbit of Neptune. Many thousands of asteroids exist in the inner solar system, so we should not be surprised that some objects have been discovered beyond the orbits of Neptune and Pluto.6 Several hundred of these ‘KBOs’ have now been observed.7 But a Kuiper Belt would need around a billion icy cores in order to replenish the solar system’s supply of comets. It remains to be seen whether KBOs exist in such abundance. Currently, this is merely an evolutionary speculation.
It should also be noted that the observed KBOs are much larger than comet nuclei. The diameter of the nucleus of a typical comet is around 10 kilometers. However, the recently discovered KBOs are estimated to have diameters ranging from about 100 to 500 kilometers.8 This calls into question the idea that these objects are precursors of short-period comets. So, the discovery of objects beyond Neptune does not in any way confirm a Kuiper Belt—at least not the kind of Kuiper Belt that evolutionary astronomers require. As such, the term ‘Kuiper Belt Object’ is a bit misleading. ‘Trans-Neptunian Object’ (TNO) would be a more descriptive term for these distant minor planets—and many astronomers use these terms (TNO and KBO) interchangeably.
Interestingly, astronomers have recently discovered that several TNOs are binary.9 That is, they consist of two objects in close proximity; these orbit each other as they orbit the sun. The tremendous controversy on the (evolutionary) origin of Earth’s moon (see The Moon: The light that rules the night) highlights the difficulty of forming (by random processes) two co-orbiting masses. Currently, giant impacts are being invoked to explain the origin of Earth’s moon as well as Pluto’s moon Charon. But these involve unlikely ‘chance’ collisions at precise angles and have other difficulties as well. Yet, we are finding that binary objects are far more common than previously thought.10 Might this point to a Creative Designer?
Some astronomers would classify Pluto as a (particularly large) Trans-Neptunian Object. Indeed, Pluto may have far more in common with TNOs than it has with the other eight planets—such as its icy composition and its orbital properties. In fact, a substantial fraction of the newly discovered TNOs have an orbital period nearly identical to that of Pluto.11 These are called ‘Plutinos’ (little Plutos). So, while Pluto is a dwarf among planets, it may be ‘King’ of the TNOs. Since Pluto’s moon Charon is so large (relative to Pluto), Pluto is often considered a binary system. As such, Pluto could be considered not only the largest TNO, but the largest binary TNO as well. As these new discoveries continue to pour in, Creationists should delight in the marvellous complexity and structure of the universe God has created.
References and notes:
- Gravitational encounters with the planets can also deplete comets. A comet might be ejected from the solar system or (more rarely) collide with a planet. Return to text.
- The Kuiper belt is named after Gerard Kuiper who proposed its existence in 1951. Return to text.
- In evolutionary thinking, a spherical ‘Oort cloud’ is supposed to explain the existence of long-period comets. Creationists would not be surprised to find some objects at that distance, but (as with the Kuiper Belt) we would question whether there are enough objects to explain the origin of long-period comets. Currently, there is no evidence whatsoever of a massive Oort cloud. Moreover, there is tremendous difficulty in forming an Oort cloud of sufficient mass (through natural processes) in the first place! Hence, long-period comets also present a serious challenge to a multi-billion year old solar system. Return to text.
- An AU (Astronomical Unit) is the average distance from the Earth to the sun. It is roughly equal to 150 million kilometers or 93 million miles. Neptune orbits the sun at 30 AU. Pluto’s distance from the Sun varies in its orbit from about 30 AU to 50 AU with an average distance of around 40 AU. Return to text.
- An object named ‘1992 QB1’ was the first KBO (or TNO) to be discovered (besides Pluto and Charon, if they are counted). Its orbital period is computed to be 296 years. Return to text.
- A handful of small objects exist in between the orbits of Jupiter and Neptune. These are called Centaurs. Chiron, for example orbits between Saturn and Uranus. Chiron was originally classified as an asteroid, but it now appears that its composition is icy — like a comet. Centaurs are not nearly as plentiful as TNOs; the proximity of the giant planets would tend to make such orbits unstable. Return to text.
- Nearly 600 KBOs have been discovered as of May 2002. Undoubtedly, more TNOs will be discovered. Recent observations suggest that these objects may taper off rather abruptly at 50 AU — and not extend to 100 AU as originally thought. See The Edge of the Solar System, 24 October 2000. Return to text.
- If such a large object were to fall into the inner solar system, it would make a very impressive comet! Alas, no observed comets have been this large. A particularly large KBO (named 2001 KX76) was recently discovered. It is over 1,000 km across—about the size of Pluto’s moon Charon. See The Kuiper Belt, Spacetech’s Orerry. Return to text.
- Seven binary TNOs have been discovered as of May 2002. See Distant EKOs: The Kuiper Belt Electronic Newsletter 22, March 2002. Return to text.
- Many asteroids are now known to be binary as well. Beattie, J.K., Asteroid Chasers Are Seeing Double, Sky and Telescope. Return to text.
- These Plutinos orbit the sun at an average distance of about 40 AU with a period of 248 years—the same as Pluto. This is no coincidence; this orbital period is particularly stable because it is a 2:3 resonance with Neptune. Pluto and the Plutinos orbit the sun twice for every three orbits of Neptune. Return to text.