(The original article can be found here.)
SUMMARY: Past explanations for how comets began have serious problems. After a review of some facts concerning comets, a new explanation for comet origins will be proposed and tested. It appears that the fountains of the great deep and the sustained power of an “ocean” of high-pressure, supercritical water jetting into the vacuum of space launched, as the flood began, the material that became comets. Other known forces would have assembled the expelled rocks and muddy droplets into larger bodies resembling comets in size, number, density, composition, spin, texture, strength, chemistry (organic and inorganic), and orbital characteristics. After a comparison of theories with evidence, problems with the earlier explanations will become obvious.
Comets may be the most dynamic, spectacular, variable, and mysterious bodies in the solar system. They even contain organic matter—including trace amounts of the amino acid glycine, a complex building block of life on earth.1 Early scientists discovered other types of organic matter in comets, and concluded that they came from “decomposed organic bodies.”2 Today, a popular belief is that comets brought life to Earth. Instead, comets may have traces of life from Earth.3
Comets orbit the Sun. When closest to the Sun, some comets travel more than 350 miles per second. Others, at their farthest point from the Sun, spend years traveling less than 15 miles per hour. A few comets travel so fast they will escape the solar system. Even fast comets, because of their great distance from Earth, appear to “hang” in the night sky, almost as stationary as the stars. Comets reflect sunlight and fluoresce (glow). They are brightest near the Sun and sometimes visible in daylight.
A typical comet, when far from the Sun, resembles a dirty, misshapen snowball, a few miles across. About 38% of its mass4 is frozen water—but this ice is extremely fluffy, with much empty space between ice particles. The rest is dust and various chemicals. As a comet approaches the Sun, a small fraction of the snowball (or nucleus) evaporates, forming a gas and dust cloud, called a coma, around the nucleus. The cloud and nucleus together are called the head. The head’s volume can be larger than a million Earths. Comet tails are sometimes more than an astronomical unit (AU) long (93,000,000 miles), the Earth-Sun distance. One tail was 3.4 AU long—enough to stretch around Earth 12,500 times.5 Solar wind and radiation propels comet tails away from the Sun, so comets traveling away from the Sun move tail-first.
Comet tails are extremely tenuous—giant volumes of practically nothing. Stars are sometimes observed through comet heads and tails; comet shadows on Earth, even when expected, have never been seen. One hundred cubic miles of comet Halley’s tail contains much less matter than in a cubic inch of air we breathe—and is even less dense than the best laboratory vacuum.
In 1998, billions of tons of water-ice mixed with the soil were found in deep craters near the Moon’s poles. As one writer visualized it, Comets raining from the sky left pockets of frozen water at the north and south poles of the moon, billions of tons more than previously believed, Los Alamos National Laboratory researchers have found.6
Later, thin traces of water were found at all lunar latitudes by three different spacecraft.7 Comets are a likely source, but this raises perplexing questions. Ice should evaporate from the Moon faster than comets currently deposit it, so why does so much ice remain?8 Also, recently deposited ice has apparently been discovered in permanently shadowed craters on Mercury,9 the closest planet to the Sun. Ice that near the Sun is even more difficult to explain.
Fear of comets as omens of death existed in most ancient cultures.10 Indeed, comets were called “disasters,” which in Greek means “evil” (dis) “star” (aster). Why fear comets and not other more surprising celestial events, such as eclipses, supernovas, or meteor showers? When Halley’s comet appeared in 1910, some people worldwide panicked; a few even committed suicide. In Texas, police arrested men selling “comet-protection” pills. Rioters then freed the salesmen. Elsewhere, people quit jobs or locked themselves in their homes as the comet approached.
Comets are rapidly disappearing. Some of their mass is “burned off” each time they pass near the Sun, and they frequently collide with planets, moons, and the Sun. Comets passing near large planets often are torn apart or receive gravity boosts that fling them, like slingshots, out of the solar system forever. Because we have seen so many comets die, we naturally wonder, “How were they born?”
Textbooks and the media confidently explain, in vague terms, how comets began. Although comet experts worldwide know those explanations lack details and are riddled with scientific problems, most experts view the problems, which few others appreciate, as “future research projects.”
To learn the probable origin of comets, we should:
a. Understand these problems. (This will require learning how gravity moves things in space, often in surprising ways.)
b. Learn a few technical terms related to comets, their orbits, and their composition.
c. Understand and test seven major theories for comet origins.
Only then will we be equipped to decide which theory best explains the origin of comets.
Some have proposed that the Moon’s crust must be thinner on the near side, so lava can squirt out more easily on the near side than on the far side. However, no seismic, gravity, or heat flow measurements support that hypothesis. The Moon’s density throughout is almost as uniform as that of a billiard ball,55 showing that little distinctive crust exists. Not only did large impacts form the giant basins, but much of their impact energy melted rock and generated lava flows. This is why the lava flows came after the craters formed. These impacts appear to have happened recently. [See “Hot Moon” on page 40.]
Large impacts would also shift rock within the moon and produce deep frictional melting. Magma produced below the Moon’s crossover depth would sink to the moon’s center and form the Moon’s small liquid core that was discovered in 2011.56 That core has not had time to cool and solidify. [The crossover depth is explained on pages 151–152.]
Contemporaries of Galileo misnamed these lava flows “maria” (MAHR-ee-uh), or “seas,” because these dark areas looked smooth and filled low-lying regions. These maria give the Moon its “man-in-the-moon” appearance. Of the Moon’s 31 giant basins, only 11 are on the far side.57 (See if you can flip 31 coins and get 11 or fewer tails. Not too likely. It happens only about 7% of the time.) Why should the near side have so many more giant impact features, almost all the maria,58 and almost all deep moonquakes? Opposite sides of Mars and Mercury are also different.59
If the impacts that produced these volcanic features occurred slowly from any or all directions, all sides would be equally hit. Only if the impacts occurred rapidly from a specific direction would large impact features be concentrated on one side of the Moon. Of course, large impacts would kick up millions of smaller rocks that would themselves create impacts or go into orbit around the Moon and later create other impacts—even on Earth. Today, both sides of the Moon are saturated with smaller craters. Were the large lunar impactors launched from Earth?
Apparently. The Moon as a whole has relatively few volatile elements, such as nitrogen, hydrogen, and the noble gases. Surprisingly, lunar soil contains these elements—and water60—suggesting that they may have come from Earth. The relative abundances of isotopes of these elements in lunar soils correspond not to the solar wind but to what is found on Earth.61 If large impactors came from Earth recently, most moonquakes should be on the near side, and they should still be occurring. They are.