They are in highly eccentric orbits around the sun, with apoapsides varying from 4 AU to 30 AU (in the Kuiper belt) and beyond. The relatively short life spans of comets have provoked a still-unsettled debate concerning their origins. This debate is one of the most important of all debates between creationists and non-creationists. It has been estimated that a typical comet can only orbit the sun for about 100,000 years depending on its size and to match this to an universe of 4.5 billion years, secular astronomers seek to invent ideas like the appearance of new comets in an oort cloud. The astronomical symbol for comets (☄) consists of a disc with a tail similar to a wig.
- 1 History of Comet Observation and Exploration
- 2 Parts of a comet
- 3 Chemical composition
- 4 The Role of Water and Water-Ice
- 5 Families of comets
- 6 Life span
- 7 Origin
- 8 References
- 9 See Also
History of Comet Observation and ExplorationChinese records mention a recurrent comet beginning in 240 BC. That comet is most likely Comet Halley, whose discoverer, Edmond Halley, was the first to predict a comet's reappearance in advance. Comet Halley also appeared on April 24, 1066, to astounded onlookers in England prior to the conquest of England by the Normans, as depicted in the Tapestry of Bayeux.
In fact, comets have been observed for far longer in history. The ancient Greeks called them "evil stars," which in Greek is dys evil and astron a star. This is the origin of the modern word disaster. The association of comets with untoward events or prophecies continued as recently as the twentieth century, when Comet Halley made an unusually close rendezvous with earth.
Parts of a comet
The nucleus or head of a comet has been directly observed as a double-lobed, dark, hard and rocky body with little to no evidence of water ice. As a comet approaches the sun at 5 AU or closer, the coma forms. This is the base of the two tails of the comet. The body begins to vaporize, and the solar wind blows the liberated particles away from the sun. The dust forms one tail, and ions form another. Note the jets in the photograph of Comet Hartley. These jets actually change from photo to photo, owing to the fact that they are not vents, but are produced on the comet's surface.
Cometary comas (and cometary explosions) have formed well-outside the boundary where solar heating could account for the activity (Comet Shoemaker-Levy 9). Comets have been known to bloom even on their outbound path (e.g. Comet ISON). These events invariably occur on the boundary of heavy solar activity such as mass ejections or increase in solar wind. Recent up-close photography has revealed that sublimation of ice cannot account for the production of the comet's coma, which can exceed the diameter of the Sun (e.g. Comet Holmes).
Comet nuclei are currently thought to measure 16 kilometers across or less. A comet nucleus has been observed has hard and rocky with no reflective properties. Light from the nucleus is produced by collumated jets. A comet's coma has an abundant hydrogen cloud around it that absorbs ultraviolet radiation and becomes fluorescent. A comet's tails can extend for 160 million kilometers and thus appear larger than the constellation of Ursa Major, and occasionally brighter than the Milky Way itself.
Since 1981, satellite-based cameras have repeatedly photographed a number of objects striking earth's atmosphere and vaporizing. These might in fact be small cometary nuclei, each as large as a house (thankfully not like Comet 67P (observed by Rosetta) as large as a city!) Remarkably, these objects tend to strike more frequently in the early fall than in the early winter. Some critics contend that these objects are mere camera noise, but experiments to replicate house-sized comets have succeeded in duplicating the observed effects.
The Stardust mission brought back findings that stunned the researchers, most prominently the lack of water-ice in the samples. In fact, no water ice was detected on the cometary body or the tail. This and more recent missions have revealed that the cometary body is composed mostly of silicates.
The presence of water on a cometary body is derived from the presence of the hydroxyl radical (OH) which can be produced when ultraviolet rays decompose water into OH and Hydrogen. The presence of hydroxyl presumes that it was derived from water. Observers have noted however, that the ratio of OH to Hydrogen on a comet is too small to have been derived by water. In laboratory experiments (and observed on the lunar surface) proton bombardment of silicates can produce large quantities of hydroxyl. As the cometary bodies are mostly silicate and the solar wind is composed of high-speed protons, this accounts for the level of hydroxyl on a comet without the presence of water at all. If no water is present on the cometary body, this overturns the notion that the comet is a "dirty snowball" and removes the need for the legendary "Oort Cloud" to manufacture them.
In 1998 and 1999, Meier et al. published at least three papers showing that comets are remarkably rich in deuterium or "heavy" hydrogen. This included deuterated water (HDO) and deuterated hydrogen cyanide (DCN) In fact they have it in twice the concentration of deuterium in the seas of earth and 20 to 100 times the concentration in the rest of the solar system. In 1998 Meier stated flatly that
|“||Comets cannot be the only source for the oceans on Earth.||”|
In July of 2004, the Stardust mission approached to within 150 miles of Comet Wild 2 and was able to sample its tail and return the samples to earth (January 2006). The returned dust was crystalline and included organic material and many terrestrial minerals. These included aluminum, magnesium, calcium, and titanium.
Of note, the following anomalous findings shocked the researchers:
- Forsterite, which requires over 1000 degrees to form. No such temperatures exist in deep space
- Pyrrhorite, olivine and sphalerite also require extremely high temperatures to form
- Olivine breaks down in the presence of water
- Iron and Cubanite, which can only form in the presence of liquid water, which in turn requires atmospheric pressure, but no atmosphere exists on a comet
- Cubanite cannot exist in temperatures exceeding 210 degrees
One year later, on July 4, 2005, the Deep Impact mission conducted the first direct analysis of the rocky portion of a comet nucleus, by launching a projectile into Comet Tempel 1. The projectile liberated much material, including silicates, crystalline silicates, minerals that normally form in liquid water (calcium carbonate forms and clays), an organic material of still undetermined composition, sodium, and a very fine powder.
Of note in the Deep Impact encounter, when the projectile approached the comet, it released an initial flash of light followed by a highly energetic burst that saturated the cameras observing the event. The original intent of the mission was to analyze the cloud of dust produced by the impact to further clarify the comet's composition. The energetic event was unexpected (by standard cosmology) so hindered the primary mission's outcome. The impact of the probe also changed one of the comet's jets, revealing that the jets are not a product of vents in the body, but originate on the comet's surface. A later fly-by of the cometary body with the NEXT probe revealed that the Deep Impact probe had not left a crater on the comet's surface. It basically bounced off after impact. The impact point, between two existing craters, was barely visible when it should have been quite large (the impact probe was about the size of a standard washing machine).
In 2014, the Rosetta mission attempted to land a probe (Philae) on comet 67P, but the probe made impact and bounced twice before landing and deploying its harpoons. The presumption of the researchers was that the body would be soft, having accreted from dust and ice. The Philae probe lost contact with the Rosetta satellite on impact, so likely experienced the same energetic impact event as the Deep Impact probe. The disoriented Philae then was able to deploy a harpoon that secured it where a prior harpoon had failed. The presumption even today is that the harpoon has secured Philae to the nucleus when it may be only simple gravity holding it in place (after having bounced twice). The harpoon implementation presumes the presence of a much softer surface, which does not exist on 67P.
The Role of Water and Water-Ice
Recent up-close observations have drawn sharp contrast between the purported standard model of comets (as dirty snowballs) versus the hard, rocky bodies that are actually observed.
Scientists have long believed that comets were composed of water-ice because of the level of hydroxyl being produced by the comet. It is commonly accepted that the hydroxyl (OH) radical "can" be the result of ultraviolet radiation on common water, breaking it into hydroxyl and hydrogen. Recent observations have noted that the comet's ratio of hydrogen to hydroxyl is too low to have water as its origin.
Laboratory experiments (and observations on the lunar surface) reveal that OH can be formed when protons bombard silicates. As comets have an abundance of silicates and are being bombarded with protons from the solar wind, this is the simplest explanation for the OH/H ratio. Otherwise the comet would have to produce over 40,000 tons of water per day to account for the level of OH and H in the comet.
If the comet has no water or water-ice, then the theory as to the sublimation of water ice (heating ice to produce the coma) is now in question if not invalidated altogether. With it goes the imaginary Oort Cloud, which was only invented to attempt to explain the longevity of comets. If comets don't last very long and were formed billions of years ago, we should not have any more comets to observe, so there must be a comet-factory like the Oort Cloud.
But if the comets were formed by ejected matter from planets in a fairly recent timeframe, this would explain their youth and still eliminate the need for water-ice and the Oort cloud. The Martian moon Phobos is now accepted as having come from the Martian surface.
While following comets and updates to new discoveries, one should keep a watchful eye on how they explain the many growing anomalies concerning comets, not the least of which is the absence of water on a body that purportedly contains huge amounts of it.
Families of comets
Astronomers today divide comets into at least two classes. The official definition of a short-period comet is any comet having a period of 200 years or shorter. Any comet having a longer period is called a long-period comet.
Walt Brown notes that 205 comets have periods of 100 years or shorter, and 659 comets have periods of 700 years or longer. He also counts 50 intermediate-period comets having periods between those two values.
Several very long-period comets, in near-parabolic orbits, are known. No comets have ever been seen in hyperbolic orbits.
Roughly 60% of all short-period comets belong to Jupiter's family. These are comets having aphelions varying between 4 and 6 AU. Other short-period comets have aphelia within the Kuiper belt. The long-period comets have calculated aphelia far beyond the Kuiper belt, at about 50,000 AU.
The perihelia of all comets vary between 1 and 3 AU.
Short-period comets tend to lie in or close to the plane of the ecliptic. Long- and intermediate comets can have any inclination from zero to ninety degrees.
By orbital direction
Short-period comets are almost all in prograde orbits. But more than half of all long-period comets are in retrograde orbits.
The following table, adapted from Brown, gives orbital characteristics and composition of the 964 comets now known:
|Period||< 100 a||100-700 a||> 700 a|
|Inclination to ecliptic||Usually low||Low to high||Low to high|
Comets have remarkably short life spans. Most periodic comets, particularly in Jupiter's family, have life spans of 10,000 to 12,000 years. A comet may make a limited number of orbits before all its volatile substances sublimate away, leaving behind an asteroid-like rock. Certain asteroid-like objects, called damocloids, in highly eccentric orbits around the sun might be inactive comets. 21 such objects are known. Some authorities estimate that half of all near-earth asteroids are in fact cometary remnants.
Brown details several evolutionary theories of the origins of comets.
- Main article: Oort cloud
Most conventional astronomers invoke the nebula theory and state that comets are debris that failed to accrete into the planets and moons when the solar system formed. The classic Oort cloud theory states that the Oort cloud, a sphere measuring about 50,000 AU in radius, formed at the same time as the solar nebula and occasionally releases comets into the inner solar system as a star (possibly the reputed Nemesis) passes. Jewitt and others have proposed instead that comets initially formed near or immediately beyond the gas giant planets. Some of these objects persist as Kuiper belt objects. Others passed close enough to the gas giants to gain sufficient energy to launch them into high orbits, where they eventually formed the Oort cloud and, some suggest, continue to resupply it.
According to this theory, the sun passes through and perturbs clouds of interstellar dust and gas. In the process it captures large numbers of particles, which accrete into comets.
Comets form continuously from a stream of meteors in various orbits around the Sun.
Comets are volcanic ejecta, from either the various gas giants or some of their moons.
A planet originally in the region now occupied by the main asteroid belt exploded about 3,200,000 years ago. The presently observed comets and asteroids are its remnants.
- Main article: Panspermia
Many comets contain organic compounds, including methane and ethane. This has led some scientists to speculate that comets brought to earth the initial "seeds" of life.
- Main article: Electric Comet
A theory that is gaining foothold in the scientific community aligns with the electrical properties of matter. The Electric Comet theory proposes that the cometary body, because of its composition of organic and other chemicals that are only found in the Solar System's Habitable Zone, are actually from one of the inner planets such as Mars or Earth. The Martian moon Phobos is now accepted as having come from the Martian surface as part of an energetic event such as impact from another body. The basic proposals and predictions of the Electric Comet theory follow:
- The nucleus was ejected from a planet after formation, not accumulated in deep space
- No difference in composition between a comet and asteroid (Schwassman-Wachmann 1 and Chiron are examples of asteroids turned comet)
- The comet "collects" negative charge while in deep space
- The comet's charge reacts with the Sun's weak electric field as it approaches
- The jets on the comet are the result of electrical discharge on the surface
- Comets will often appear as double-lobed, since this is a natural side-effect of electrical discharge activity
- The coma is the result of a double-layer effect (natural effect of charge-separation between bodies)
- The nucleus has little to no water in its composition
- The nucleus will be a hard, rocky body, replete with "sharp relief" of mesas, cliffs, and a "tortured" surface
- The nucleus will be replete with craters that were carved from electrical activity, not impact-craters
- The nucleus is of fairly recent origin, not a leftover from the origin of the Solar System
- Since comets haven't been here very long, speculations as to their age are meaningless
- In 1996, the NASA Swift observatory saw comet Hyakutake emitting x-rays, which are normally seen with very hot plasmas and was an unexpected discovery, but are expected if the comet is causing an energetic electrical discharge between itself and the Sun.
- When viewed side-on, the x-ray emission of the comet appears as a sheath that remains between the comet nucleus and the Sun.
The implications of the Electric Comet are profound in that they undermine the standard model of cosmology and set-aside many of the modern musings of science concerning the earth and cosmos. These include the following:
- The age of the universe is not knowable (could be young, could be old)
- The Solar System did not form with "accretion disks"
- The Sun and planets appeared more recently than standard cosmology asserts
- Stars do not form with accretion disks or with any mechanism proposed by the standard model
- Stars (and the Sun) are formed and powered by very-large-scale, galactic-level electrical circuits, not thermonuclear energy
- Rejects gravity as the primary force of the universe, instead embracing electromagnetism
- Rejects the thermonuclear-powered Sun in favor of the Sun behaving as an electrical transistor to large-scale Birkeland currents
- From papers on their sites, they strongly question the viability of Darwinism
- Strongly question the viability of many aspects of Einstein, and reject the notion of the Oort Cloud, Black Holes and Dark Matter
- Reject the idea that mathematics trumps observation, challenging the current direction of cosmology where mathematics and computer models attempt to explain the cosmos in ways that defy actual observations
- X-Rays, Gamma-Rays and ultraviolet light are predicted as standard and commonplace where the standard model does not expect such energetic outputs at all.
The above seems to form an alignment with creationism, so is tempting to embrace. However, there is no affinity for creationism among the proponents of these theories. They often align with observations that dovetail with creationist predictions, but seem to have an underpinning philosophy that is atheistic. The reader is cautioned to be circumspect and wise about how such observations align with the creation model without wholesale endorsement of these theories and perhaps even their underpinning assertions about origins that may (or may not) include a personal Creator. For example, their web sites include a paper containing a scathing critique of Darwinism from a secular scientist. While the critique is accurate and compelling, this scientist later proposes that DNA came from a giant, ancient machine (about the size of a planet) that has gone about the universe, impersonally seeding it with life forms.
Problems for uniformitarian theories
Many comets have life spans less than 10,000 years. According to the nebula theory, comets formed with the rest of the solar system, 4.6 billion years ago. Adherents of the interstellar capture theory try to connect the origin of cometary matter with the big bang, which, they say, happened about 13.7 billion years ago. But in that case, all the short-period comets ought to have disappeared. This is especially true of the Jupiter family. Even if the Kuiper belt is the source of short-period comets, such comets would have to lose much kinetic energy in order to settle into the short-aphelion orbits of Jupiter's family. This begs the question of how and where they lost this energy.
Brown lists many other problems for various uniformitarian theories posed by comets:
- Comets are composed of silicates and minerals only found in the Solar Systems Habitable Zone, and are hard, rocky bodies with no evidence of large quantities of water or water-ice. Accretion from a solar nebula has never been satisfactorily modeled. Accretion requires the sudden release of a stream of matter beyond the sphere of gravitational influence of another body, and into a region in which the matter can form its own, rapidly growing sphere of influence. The putative conditions of the solar nebula do not meet this requirement.
- Crystalline dust might form from an exploded planet, but it would not be likely to form in any of the other proposed models.
- If comets formed in the region of the putative Oort cloud, they would not attain near-parabolic orbits.
- The original Oort cloud model and the interstellar capture model would tend to produce perihelia with predictable alignments. The perihelia of comets are almost completely random.
- Either of the Oort cloud models would be expected to produce comets with hyperbolic orbits. No such cometary orbit has ever been observed.
- The observed perihelia, varying from 1 to 3 AU, are incompatible with any origin of comets beyond 3 au. Therefore, comets would have to form in the main asteroid belt or closer to the sun.
- The Oort cloud, if it exists, cannot be the source of short-period comets. But Gerard P. Kuiper formed the hypothesis of the belt of objects that bears his name to explain this discrepancy.
- Jupiter's family of comets cannot have come from a planetary explosion at 3 au from the sun, or from any other source described above other than volcanic ejection from Jupiter.
- If comets formed in the gas giant region and were later launched into the Oort cloud, many of the comets now observed would have destroyed one another long ago.
- The current composition of comets cannot have resulted from volcanic ejection from a gas giant.
- The unusual proportion of deuterium in comets, and only in comets, makes their origin from either the solar nebula or an interstellar dust cloud very problematic. The preferential concentration of deuterium is the most difficult observation to explain.
- The small comets recently observed striking the earth should not be observed if comets originated beyond 3 AU.
- The observed meteor craters are mostly superficial and thus inconsistent with a formation of comets within the inner solar system millions or billions of years ago. This militates against the exploded-planet and revised Oort cloud models.
For further details, see Brown's table of various comet-origin theories and how well (or poorly) they explain the evidence. Also pay attention to Brown's explanation in terms of water and ice being the primary composition of a comet. Brown proposes that large amounts of water and matter were ejected from the Earth's surface, the water having formed the comets. However, if current observations are accurate and little to no water exists on a comet's nucleus, this does not set-aside Brown's assertion, but merely re-aligns the comet's source as having come from the planetary matter and not water. Comets are composed of minerals and silicates that could only have formed along with a planet. So it makes sense that large chunks of matter were ejected (in Brown's model) and that some of these became the comets we see today. Water does not play a primary role in a comet, and many are observed with no water at all.
- Main article: Hydroplate theory
Brown proposes a radically different theory for the origin of comets: that they originated from matter ejected into space during the global flood. According to his hydroplate theory, the Flood waters broke through a crustal rupture that persists today as the Mid-Oceanic Ridge system. This water was extremely hot and under tremendous pressure. Brown estimates that less than one percent was ejected into space. In the process, the edges of the crust at the rupture crumbled, and much of their material was ejected with the water.
The ejecta easily reached escape speed and soon passed beyond earth's gravitational influence. Some of the rocks abruptly formed spheres of influence of their own and attracted the surrounding water through gravitational accretion. Brown calculates that the ejecta included enough mass for 50,000 comets, far more than have thus far been observed.
Much of the water fell onto the moon and the planets Mercury and Mars, where it condensed and froze in the polar regions. The hydroplate theory also states that many of the rocks fell to the moon and thus created the craters and maria observed today.
Many of the comets were ejected into hyperbolic orbits, never to return to the inner solar system. Others were launched into near-parabolic orbits, either immediately or under the influence of the gas giants.
The high concentrations of deuterium reflect the initial composition of the subcrustal oceans. The organic matter came from earth and was never introduced to earth by the comets.
Problems for the hydroplate theory
The hydroplate theory has two known problems:
- Near-parabolic comets often have very long periods. Their launch in an event occurring 4400 years ago is difficult to explain. But any of them might have received a gravitational boost from Jupiter or some other gas giant. In addition: whenever any object passes beyond the orbit of another body in the solar system (especially a gas giant), it then becomes subject to the additional gravitational pull of that object, in addition to any other object nearer the sun than the index object happens to be. So a comet might appear to have a period longer than the projected history of the earth. But that period assumes a constant combined "primary" mass. When a comet passes Jupiter, Saturn, Uranus, Neptune, and then the Kuiper Belt, it violates that condition. So such a comet has a shorter period than one would otherwise predict. When it falls back to the sun, and once again moves inside the various objects, it is no longer subject to their gravitational influence.
- Humphreys followed up on his model for the creation of planetary magnetic fields and calculated that the moon suffered two bombardments, neither of which were in time frames compatible with the global flood. According to Humphreys, the maria formed three centuries after the fall of man, and the visible craters formed about a century or so after the flood. If most of the comets, asteroids, and meteoroids now observed were flood ejecta, then they could have subjected the moon (and other moons in the solar system) to a heavy bombardment a century later and formed the craters. But they could not have formed the maria. Or could they? Humphreys' model has its own problems, not least of which is that it does not take into account the presence of the "mass concentrations" on the Moon that can only remain from seven heavy impacts that were strong enough to:
- Drop the Moon into a lower orbit, and
- Lock the moon tidally to the earth.
These problems, in any case, are distinctly minor in comparison to the great number of critical difficulties for uniformitarian theories.
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