18 October 2001
Comet Borrelly rocks core scientific beliefs
The above headline accompanied the news item in the Sydney Morning Herald of 9/27. Comet Borrelly has been visited by the aging Deep Space 1 (DS1) spacecraft and the clearest pictures to date of a comet nucleus returned. It was a tremendous engineering feat to nurse the spacecraft to this rendezvous. However, despite the headline it seems certain that the core scientific beliefs of NASA scientists will not be disturbed. The reason is that core beliefs are often so ingrained that they are unrecognized.
"Comets are perhaps at once the most spectacular and the least well understood members of the solar system." Marcia Neugebauer, JPL
Comet Borrelly. Inset are the jets and a crater on the terminator. Image credit: NASA/JPL
Astronomers are already saying that the pictures of the 10-kilometre- (6-mile-) wide core of Comet Borrelly will revolutionise our understanding of these frozen wanderers. DS1 passed within 2,000 kilometres (1,200 miles) of the comet's rocky, icy heart late on Saturday September 22 GMT.
Here is the first core belief to remain unquestioned - a comet has been held over in deep freeze beyond the solar system since the time the planets were formed. Then, after billions of years, somehow it has been deflected into the inner solar system.
Comets are believed to enter the inner solar system when disturbed from an invisible cloud of icy objects located about 1000 times the distance of Pluto, a good fraction of the way to the nearest star. The disturbance is thought to be due to a passing star or the movement of the Sun above and below the galactic plane. But many astronomers have pointed to the lack of evidence for sporadic comet showers that such disturbances should unleash and concluded that such events could only account for about one-fifth of the comets we see. The astronomer, Tom Van Flandern, has devised a scale model that demonstrates the silliness of this theory. If the Earth's orbit were represented by the period at the end of this sentence and Pluto's orbit by a circle of one centimetre diameter, then the nearest star is 41 metres away. The Oort cloud of comets would orbit near a sphere 6 metres in diameter containing one comet per cubic millimetre. The comets would move at about 3 millimetres per 1000 years. They are effectively motionless. Passing stars on rare occasions 'whiz' past at a metre per 1000 years and stir up the nearby comets. Less than 1 in 10,000 disturbed comets will be knocked onto a path that will target the 1 millimetre or so sphere surrounding the Sun where a comet might be seen from the Earth. Having visualized this, Van Flandern makes the point that the true size of a sphere encompassing Pluto's orbit is so vast that all of the 200 billion stars in our galaxy would fit with room to spare in that volume. He writes, "But the volume enclosed by the comet cloud is a billion times greater yet. It truly is unimaginably large, surviving as a plausible idea in large part because our intuitions fail so miserably to comprehend the vastness of this volume." One serious observational difficulty with the model is the total lack of comets on hyperbolic orbits. And like other examples in astronomy it is a theory based on invisible matter.
"The Oort-shell, ...has become widely regarded as a firmly established triumph of 'modern cometary theory' when in fact, it is a piece of trash heralded as one of the corner-stones of cometary 'science'." Journey to the Centre of Uncertainty, Prof. R A Lyttleton, Speculations in Science & Technology, Vol. 8, No. 5 p. 343.
DS1 sent back black-and-white photos, as well as data on gases and infrared waves around the comet, and how the gases interact with the solar wind (the process that drives a comet's characteristic tail).
Here is the second core belief that will not be questioned - the solar wind is merely a wind that blows the gases from a comet away from the Sun to form a tail. The tail should disperse like smoke in a strong wind. This highlights the third and fundamental core belief that all objects in the universe are electrically neutral.
In May, 1996, the Ulysses spacecraft, which is studying the Sun, surprised scientists when it encountered the ion tail of Comet Hyakutake. The comet was then 360 million miles from the spacecraft! That is four times the distance of the Earth from the Sun. To remain intact over that distance the tail of a comet must carry electrical current to prevent its dispersal. That is because an electric current in space takes the form of a twisted filament known as a "Birkeland current", rather like an invisible braided copper wire. When the current is strong enough such filaments are visible. They can be seen when comets are close to the Sun and they are ubiquitous in images from deep space. They may stretch, in the former case, over interplanetary distances and in deep space over intergalactic distances. The notion that all objects in the universe are at the same electrical potential - zero, has kept astrophysics firmly in the seventeenth century, with Isaac Newton. The solar wind does not "drive" a comet's tail mechanically. Observations show that a comet is highly negatively charged with respect to the Sun. It behaves like a classical "cold cathode" in a vacuum.
Comets exhibit odd orbital behaviour due to what is euphemistically known as a "non-gravitational" force. The obvious suggestion was made that cometary jets act upon the nucleus to modify its orbit. However, it is natural for a charged body to experience an electrical acceleration in the Sun's weak radial electric field. It is also natural for spacecraft, which become electrically charged and do not have jets to experience a "non-gravitational" acceleration. That is precisely what has been observed. Cometary jets are not required to cause the anomalous acceleration of comets.
"Deep Space 1 plunged into the heart of Comet Borrelly and has lived to tell every detail of its spine-tingling adventure," said project manager Dr Marc Rayman. "The images are even better than the impressive images of Comet Halley taken by Europe's Giotto spacecraft in 1986." "Up to Saturday night, we had only one example of a comet's nucleus. Now, we have another one, and with it a much better understanding of comets," said Dr Don Yeomans, of the American space agency's (NASA) Jet Propulsion Laboratory, at a press conference to unveil the images. "It's mind-boggling and stupendous," said Dr Laurence Soderblom, the leader of DS1's imaging team. "These pictures have told us that comet nuclei are far more complex than we ever imagined. They have rugged terrain, smooth rolling plains, deep fractures and very, very dark material."
A fourth core belief is that comets are merely inert, dirty snowballs evaporating in the heat of the Sun.
Fred Whipple. Photo Smithsonian Astrophysical Observatory, courtesy Dr. Whipple
The dirty snowball model of comets was proposed by Fred Whipple in 1950 and has since become dogma. His words are inscribed on a microchip riding on the Stardust spacecraft, on its way to a rendezvous with Comet Wild-2 in 2004: "Today we know that comets are black and cold, consisting of ices and dust that coalesced from an interstellar cloud as it collapsed to form the solar system." Actually, as argued above, we know no such thing. The ices were required to explain why comets formed huge comas and tails as they neared the Sun. But it was obvious that something was wrong with such a simple heating model when in 1991 Comet Halley flared up between the orbits of Saturn and Uranus - fourteen times further from the Sun than the Earth. The images showed that the 15 kilometre nucleus had ejected a cloud of dust that stretched more than 300,000 kilometres. Cometary scientists were baffled by the outburst because the usual explanation of solar heating of ices cannot work at that distance. The comet is effectively in deep freeze. However, the electrical explanation fits the observation that the Sun was very active at the time. The negatively charged comet acts as a focus for the bursts of protons in the solar wind. The result is electrical erosion of its surface and the formation of a coma.
Ices are not required to drive the comet jets. Ices cannot explain the narrow jets nor the corkscrew shape they sometimes take. Comet Hale-Bopp emitted more dust than could be explained by subliming ices. Further evidence that a comet is a cathode and emits electrons came from the puzzling discovery of negatively charged atoms in the inner coma of comet Halley. The problem for the inert comet model is that these ions are easily destroyed by solar radiation and therefore require an efficient production mechanism that is not available from solar heating. In the electrical model there is a high density of emitted electrons and neutral atoms available near the nucleus to form negative ions. Negative ions may form the sunward "spike" seen occasionally from comets.
The low density calculated for some comets seems, at first glance, to support the dirty snowball model of comets. However, there is no difference between the appearance of a comet nucleus and an asteroid. One schizoid object, Chiron, has been called both an asteroid and a comet at different times. Yet asteroids are thought to be much more evolved bodies than comets. The Electric Universe proposes that their origin is identical and that a cometary display is due entirely to highly eccentric motion of a charged body in the radial electric field of the Sun. And if gravity is a dipolar electrical effect in matter then G is not a constant and it is possible that the mass of a highly negatively charged body will measure less than that of the same body when uncharged. As a result the calculated density will be low and it will not reflect the true composition of the comet (or asteroid, moon, planet, etc).
Comet Borrelly's surface darkening may result from the effects of the electrical discharge on surface material - just as we see on Jupiter's moon, Io, at the base of its electrical jets. On the other hand, the bright areas seem to be where the active jets originate. That brightness may not simply be reflected light but instead a gleam from "St. Elmo's fire" type surface discharging. The puzzling star-like appearance of some comet nuclei can be explained by surface arcing.
The Comet Borrelly images have thrown up several surprises. As DS1 flew through the coma, the cloud of dust and gas surrounding the nucleus, scientists had expected that the solar wind would flow symmetrically around the cloud, with the nucleus in the centre. But they found that although the solar wind was indeed flowing symmetrically around the cloud, the nucleus was off to one side, shooting out a great jet of material. "The shock wave is in the wrong place," said Dr Rayman. "We have to understand that." Dr David Young, of the University of Michigan, added: "The formation of the coma is not the simple process we once thought it was. Most of the charged particles are formed to one side, which is not what we expected at all." One commentator said that it was like finding the shock-wave from a supersonic jet in the wrong place - a mile to the side of the aircraft!
A fifth belief is that a comet is simply a supersonic object moving through the solar wind. And a sixth belief is that ices on the surface of a comet nucleus sublime in the Sun's warmth to form a huge enveloping cloud of gas.
Scientists were surprised when Giotto images of Comet Halley showed that the dust and gas was being emitted from just a few small craters on the sunlit nucleus. Comet Borrelly showed the same behaviour. It has been said that the human facility for self delusion is the most highly developed of all. One of the finest examples is when scientists explain the pencil thin jets from a comet as the sublimation of ices from the bottoms of craters. The presence of neatly circular craters on a comet nucleus is oddity enough, if gas is merely blowing off bits of a dirty crust. The craters would need to be more like gun barrels than pits to form thin jets. There is also the problem of concentrating the heat of the Sun at the bottoms of holes that are not pointing at the Sun. To make it more difficult, the dark, heat absorbing regions are not where the jets are issuing from. As for the off-center coma, in 1985 the International Cometary Explorer (ICE) spacecraft found that cometary effects were asymmetric around comet Giacobini-Zinner. So it seems symptomatic of rigid scientific beliefs that NASA scientists were caught again by surprise in 2001!
The answer to all of these conundrums is simple if a comet is highly negatively charged with respect to the Sun. As the comet accelerates toward the Sun electrons begin to be stripped from the nucleus like a "cold-cathode". It develops a visible glow discharge and Birkeland current tail. These electrical effects we call a comet. At some point, more powerful arcs strike on the comet nucleus and give rise to "cathode-jets" which move about and burn circular craters. The electrical discharges to a cometary cathode will follow the magnetic field lines in the vicinity of the comet. So it will be interesting to compare the jet directions with the solar wind field direction which, because it spirals out from the Sun, does not coincide with the comet-Sun line. There is no "shock wave" to be understood in the usual sense. A charged body in the plasma of space will form a sheath to protect itself from its electrical environment. The boundary of the comet's coma defines the virtual anode region of a plasma glow discharge. Electrons are accelerated outward and positive ions inward across the sheath. Strong X-rays are generated where these particles recombine.
No one expected comet Hyakutake to be a powerful source of x-rays. "Astronomers using ROSAT (the European Space Agency's Roentgen satellite) decided to look at Hyakutake and they were shocked by what they saw. ROSAT images revealed a crescent-shaped region of x-ray emission around the comet 1,000 times more intense than anyone had predicted." Dr. Michael J. Mumma wrote, "We had no clear expectation that comets [would] shine in X-rays." Some astronomers wondered why they would bother pointing an x-ray telescope at a comet. The x-rays were as intense as those ROSAT usually picks up from bright x-ray stars and they flickered like a fluorescent-tube on a time scale of hours. Flickering effects in plasma discharges are normal because of the non-linearity in its current carrying ability. Meanwhile another ad hoc proposal had to be dreamt up to explain the x-rays. So the Sun was made entirely responsible for the x-rays by suggesting that highly ionized atoms from the solar wind were scavenging electrons from the cometary atmosphere and the energy available from that recombination was sufficient to generate the observed x-rays. But that constitutes an electric current into the comet which is unsustainable if a comet is supposed to be electrically neutral.
Deep Space 1 took measurements with its plasma instruments between 90,000 kilometers (56,000 miles) and 2,000 kilometers (1,200 miles) away. These data show that the flow of ions around the comet's rocky, icy nucleus is not centered on the comet's nucleus as scientists expected before the Borrelly flyby. Ions in the turbulent flow are heated to about 1 million Kelvin (2 million degrees Fahrenheit).
Turbulent flow in supersonic shocks has become the catch-all for astrophysicists when confronted with energetic processes away from stars in deep space. The extreme temperature calculated for the ions is based on the assumption that their motion is random, in other words, thermal. If the motion is not random but is accelerated in an electric field, the notion of temperature is entirely misleading and inappropriate. The detection of a forbidden oxygen line at 1128 in cometary comas is consistent with the presence of an intense electric field. At comet Giacobini-Zinner ICE detected ions around the spacecraft in very highly collimated beams (electric currents) coming from the direction of the Sun. The shape of the comet's coma is determined principally by the electrical stresses near the comet and the resulting active discharges, or cathode jets. It is not simply a supersonic shock front. It is also obvious that a tiny piece of rock cannot have significant gravitational influence on a coma of gas that may be up to several million kilometres in diameter and entrain more mass than the comet nucleus. Far more powerful electrical influences provide a simple answer.
The highest-resolution image of the nucleus of Comet Borrelly shows a variety of terrain, including mountains and fault structures. Darkened material is visible over the surface.
The surface complexity of the comet nucleus is due to electrical arc erosion. The "fault structures" are chains of cathode arc craters. The negatively charged comet nucleus behaves as a cold cathode, which has electrons stripped from high points on its surface by the strong electric field near the nucleus. When first seen, comets are in the "glow" discharge mode. As it closes on the Sun, the comet discharge switches to the arc mode. This results in a number of high current density, bright cathode "spots", which burn a circular pit or crater into the comet's surface. Each spot is associated with a "cathode jet". The narrow jet electrically accelerates the evaporated material into space. Cathode spots tend to "jump" around on the cathode surface, giving a flickering effect and forming crater chains. Comet Borrelly seems to be covered in such pits and crater chains. As the comet nucleus rotates, spots will switch off and on because the electric field is strongest on the sunward side. This behaviour has fueled the story of ices subliming in the sunlight.
Phobos has been described as a captured asteroid. If the electrical model is correct, comet and asteroid origins are the same. So the surfaces should be directly comparable. Here can be seen crater chains and larger circular craters. Particularly striking is the crater chain to the right of center which curves sharply and terminates on a larger crater. Note the similar morphology to Schröter's Valley. Crater chains are routinely misinterpreted by geologists as indicative of sub-surface faults. Neither impacts nor faults explain this feature.
Comet Borrelly was 200 million kilometres from the Sun at the end of September 2001.
In 1871 Professor W. Stanley Jevons, noted author of The Principles of Science (1874), wrote that several of his colleagues "asserted that comets owe many of their peculiar phenomena to electrical action." That was in the days before modern scientific beliefs disallowed such speculation. Today, astrophysicists are spooked by calculations of the energy required to separate bulk positive charge from negative charge. So more than a century later they treat all astronomical objects as electrically neutral despite the obvious signatures of electrical discharge shown by comets and larger bodies. The adherence to this core belief has crippled astrophysics. The result has been a plethora of science-fiction stories about neutron stars, dark matter and black holes. They are only required by the mathematics when the almost infinitesimal force of gravity is used as the chief driving force of the cosmos. On the other hand, a good theory is one that coherently explains all of the observed phenomena and predicts outcomes of better observations and experiment. The surprise upon each new discovery shows that our modern story of comets is a poor fable. A revolution in our understanding of comets will only occur when the unconscious core beliefs are questioned.
In future: There is a plan for a comet mission called Deep Impact. Scheduled for July 2005, Deep Impact's spacecraft will arrive at comet Tempel 1 and become the first mission to impact the surface of a comet. A 350-kg (770-lb) copper mass impactor will create a spectacular football field-sized crater, seven stories deep on a comet 6-km (approximately 4 miles) in diameter. This is the first attempt to peer beneath the surface of a comet to its freshly exposed material for clues to the early formation of the solar system.
Given the erroneous standard model of comets it is an interesting exercise to imagine what surprises are in store for astronomers if the plan is successful. The electrical model suggests the likelihood of an electrical discharge between the comet nucleus and the copper projectile, particularly if the comet is actively flaring at the time. The projectile will approach too quickly for a slow electrical discharge to occur. So the energetic effects of the encounter should exceed that of a simple physical impact, in the same way that was seen with comet Shoemaker-Levy 9 at Jupiter. Changes to the appearance of the jets may be seen before impact. The signature of an electrical discharge would be a high-energy burst of electrical noise across a wide spectrum, a "flash" from infra-red to ultraviolet and the enhanced emission of x-rays from the vicinity of the projectile. The energy of a mechanical impact is not sufficient to generate x-rays.
If the arc vaporizes the copper projectile before impact the comet will not form the crater expected. On the other hand, any copper metal reaching the surface of the comet will act as a focus for an arc. And copper can sustain a much higher current density than rock or ice. There would then be the likelihood of an intense arc, with possibly a single jet, until the copper is electrically "machined" from the comet's surface. Copper atoms ionized to a surprisingly high degree should be detectable from Earth-based telescopes. Electrical discharges through the body of a poor conductor can be disruptive and are probably responsible for the breakup of comets. It is not necessary for them to be poorly consolidated dust and ice and to simply fall apart. So there is some small chance that astronomers will be surprised to see the comet split apart, if the projectile reaches the surface of the comet and results in an intense arc.
The Deep Impact mission seems rather pointless when the cathode arcs are doing the job of exposing the comet's subsurface. However, if comets are an electrical phenomenon and have nothing to do with the formation of the solar system then astronomers are bound to be baffled once more. And that could be worth every dollar NASA spends on Deep Impact.