Details Relating to the Original Oort Cloud Theory
30. 
Formation Mechanism,
Heavy Hydrogen. According to this theory, comets, as well as the rest of the solar system, began as a cloud of dust and gas (including water vapor) orbiting the Sun. If so, the ratio of heavy hydrogen to normal hydrogen in comets should be typical of the rest of the solar system; instead, it is 20 times greater.
Supposedly, solar radiation never broke apart (or dissociated) the water vapor, because it was shielded by dust particles. Water vapor could then condense as frost on the dust. However, in a virtual vacuum, dust particles coated with ice would have tiny, fixed spheres of influence, so they would not capture each other to form larger clusters—let alone comets—even over billions of years. Instead, rare collisions would scatter particles held together by their weak mutual gravity. No experimental evidence has shown how, in the vacuum of space and in less than several billion years, billions of tons of particles can merge into even one comet—much less 1012 comets. (A similar problem exists for planets.) Also unexplained is how interstellar dust formed.
31.
Ice on Moon and Mercury. Same as item 14.
32.
Crystalline Dust. Dust that formed in outer space should be noncrystalline. Comet dust is crystalline, so it did not form in outer space as this theory assumes.
33.
Near-Parabolic Comets. If comets have been falling in from an Oort cloud for only a few million years, let alone since the solar system supposedly evolved 4.5-billion years ago, many long-period comets should be coming in for the second, third ... or one hundredth time. There is a recognized lack of such comets. Almost all are falling in for the first time. [See Figure 12 on page 318.]
Some believe we do not see second-pass comets because the Oort cloud was perturbed recently. This overlooks the presence of many comets in Jupiter’s family and the absence of a perturbing star. [See Item 44 below.]
34.
Random Perihelion Directions. If a passing star did stir up the Oort cloud, causing many comets to fall toward the Sun, comet perihelions should cluster on one side of the Sun. Actually, comet perihelions lie on all sides.121
35.
No Incoming Hyperbolic Orbits. If passing stars or other gravitational disturbances “shake” comets from an Oort cloud, some of those comets should have obvious hyperbolic orbits as they enter the planetary region. None have been reported, so there is probably no Oort cloud.
Comets that formed around other stars should also be ejected by any passing stars. Such interstellar comets should enter our solar system every year or two—on hyperbolic orbits. Because incoming comets with hyperbolic orbits have never been seen, the formation processes described above probably do not happen. Leading advocates of the Oort cloud theory acknowledge this problem.31
36.
Small Perihelions. Using the scale in Figure 15 on page 330, visualize comets in an Oort cloud 1/5 mile from the blue circle representing the inner solar system. Perturbations from a passing star that far away would not be precise and delicate enough to cluster comet perihelions inside the tiny blue circle that, on the same scale, is less than an inch in diameter.
Fernández122 and Weissman123 showed, using Oort cloud theories, that perihelions of near-parabolic comets would not cluster in the 1–3 AU range (inside the blue circle), yet they do. Instead, the number of perihelions would increase as their distance from the Sun increases.
37. 
Orbit Directions and Inclinations. Explaining how planets evolved is difficult enough, but at least they have some common features, such as prograde orbits in planes near the ecliptic—all within 30 AU of the Sun. Also, to evolve comets 50,000 AU from the Sun, moving in randomly oriented planes, and with some in retrograde orbits, would require even more mysterious processes. Most long-period retrograde comets that “evolved” into short-period comets should still be retrograde. Very few short-period comets are retrograde. [See Table 12 on page 316.]
Long-period comets are inclined at all angles and rarely become short-period comets. A slight majority of observed long-period comets are retrograde. However, almost all short-period comets are prograde and lie near Earth’s orbital plane. Gravitational interactions with planets might decrease some periods, but would not change retrograde orbits at all inclinations into prograde orbits near Earth’s orbital plane.
38.
Two Separate Populations. An Oort cloud only 10,000 AU away would be too tightly bound to the Sun to allow enough stellar perturbations for this theory to work. If the cloud were 50,000 AU away, passing stars and galactic clouds would disperse the Oort cloud in a few billion years. Fernández recommended a distance of 25,000 AU, because it allows the most comets to pass through the inner solar system after 4.5-billion years. Even if that much time were available, only about 1% of the short-period comets we see would be produced. Notice that 25,000 AU is inconsistent with Oort’s 50,000 –150,000 AU estimate that gave birth to this theory.
39.
Jupiter’s Family. Comets falling in from 50,000 AU would reach very high speeds. The only way to slow them down enough to join Jupiter’s family is by gravitational interactions with planets. However, tidal effects would tear most comets apart or fling them out of the solar system. Those that slowed down over many orbits would continually risk colliding with planets and moons while slowly vaporizing with each passage near the Sun. Few comets would survive and join Jupiter’s family.
Comets in Jupiter’s family have an average life span of only about 12,000 years. They could not have accumulated over millions of years.
40.
Composition. Same as item 40 on page 335.
41.
Small Comets. See item 17 on page 332.
42.
Recent Meteor Streams. See item 9 on page 331.
43.
Crater Ages. If an Oort cloud were populated with about 1012 comets 4.5-billion years ago, the Earth should have been heavily bombarded. The further back in time, the greater the bombardment rate. Craters or other evidence of this bombardment should be increasingly visible in the deeper sedimentary rock layers, but craters are almost exclusively found in surface layers.
44.
Other/Missing Star. If a passing star deflected comets in an Oort cloud toward the Sun, where is that star? Our nearest star, Proxima Centauri, is 4.3 light-years away, or 270,000 AU. It, and the two stars gravitationally bound to it, could not have stirred up an Oort cloud, because they are moving toward the Sun, not away from it. A study that projected stellar motion back 10-million years found that no star would have come within 3 light-years of the Sun. Therefore, no star would have stirred up an Oort cloud 0.8–2.4 light-years away during the last 10-million years.124 Wouldn’t two passing stars be needed—one to produce prograde comets and another to produce retrograde comets?
45.
Other/Stripped Oort Cloud. Clube and Napier have estimated that after 200-million years of travel in its galactic orbit, the solar system should have passed through or near up to 5,000 galactic clouds (molecular clouds) whose mass is about a half million times greater than the Sun. Each cloud’s gravity could be expected to strip away 25-90 percent of an Oort cloud, because the Oort cloud is supposedly so far from the Sun. The Oort cloud should have essentially disappeared long ago.125 (Oort cloud theories have many variations; only the best known are described here.)