The currently popular models for the origin of the solar system propose a rotating cloud of gas and dust as the common source of all components of the system. According to these theories, from time to time a gaseous ring separated from this rotating matter and condensed into a planet. The leftover central material then became the sun.
Since these models propose that all planets of the solar system originated from a common reservoir of material, they foster an expectation that the com position of the planets is similar. But in fact the nine planets can be divided into two distinct groups according to their composition the so-called "inner" and "outer" planets. The "inner" planets (so named because they are closest to the sun), Mercury, Venus, Earth, and Mars, are composed of substances considerably more dense than the outer five planets. However, even within the inner planets, marked diversities have been observed.
Invasion of Venus
In December of 1978, Venus, our nearest planetary neighbor, was invaded by six U.S. and two Soviet spacecraft. Five of the six American Pioneer Venus probes were designed to measure the temperatures, pressures, and winds of the Venusian atmosphere, besides sampling cloud and atmospheric components during their plunge to the planet's surface. Surprisingly, one of the five probes survived the crash landing and continued to transmit radio signals for over an hour, despite surface temperatures of 850 F. and pressures nearly one hundred times greater than that of Earth's atmosphere. The sixth vehicle, an orbiter, continues to circle the planet and radio back useful data. Among other tasks, it scans with radar a different section of Venus' surface on each orbit; this will eventually produce a complete topological map of this planet. The other two probes, the eleventh and twelfth of the Soviet Venera series, soft-landed on Venus with the help of parachutes and continued to operate for more than an hour and a half.
Even before these space probes, scientists knew that Venus is vastly different from its neighbors of the solar system. The results obtained from the Pioneer and Venera missions confirm this, but also indicate that Venus is more complex and even more mysterious than expected.
Venus is wrapped in a continuous, thick, three-layered cloud cover, ex tending vertically from forty-eight to seventy kilometers above the surface. The upper cloud region is made up of a fairly concentrated solution of sulfuric acid. The middle and lower clouds consist of liquid droplets and solid particles of varying sizes, containing several forms of sulfur and other unidentified chemicals.
The lower thirty-two kilometers of the Venusian atmosphere is remarkably clear of any particulate matter. How ever, owing to its peculiar chemical composition, this atmosphere bends visible light so sharply that if we were looking toward the Venusian surface from orbit, we could see nothing but an empty sky!
There is a distinct glow in the lowest ten kilometers of the atmosphere, believed to be a result of some form of chemiluminescence that cannot be explained with our limited information. The Russian probes reported numerous lightning discharges and extensive rumbles of thunder in the atmosphere near the surface. Again, we do not yet under stand the reasons for these.
Both Earth and Venus receive comparable amounts of energy from the sun, yet the surface temperature of Venus is an incredible 850 F., in spite of the fact that less than 2 percent of the solar radiation reaches the surface! It is believed that a highly efficient type of "green house" effect is responsible—the carbon dioxide, water vapors, and sulfur dioxide of the atmosphere prevent the loss of absorbed solar radiation energy. It could be that additional but as yet unknown reasons also contribute to this high surface temperature.
The chemical composition of the Venusian atmosphere varies with altitude. At 150 kilometers above the surface carbon dioxide, carbon monoxide, molepular nitrogen, atomic oxygen, and helium are the dominant substances. Closer to the ground the space probes found that carbon dioxide made up 90 percent of the atmosphere, together with 3.5 per cent nitrogen, a tenth of a percent water, and even-smaller quantities of molecular oxygen, argon, neon, and sulfur dioxide.
The oxygen problem
The discovery of significant amounts of oxygen in the Venusian atmosphere was a surprise to scientists. Evolutionary models of planetary atmospheres generally call for oxygen-free atmospheres, for it is only in the absence of oxygen that the postulated transformations of chemical evolution could occur.
In the case of Venus, puzzled scientists ask, "Where did the oxygen come from, if it was not present originally?" The ultraviolet rays of the sun normally change carbon dioxide to carbon monoxide and oxygen. Water molecules change to hydrogen and oxygen. But be cause of the thick cloud covering on Venus, much of the ultraviolet radiation is blocked out, especially near the surface. In addition, neither the amounts of carbon monoxide (the substance left from carbon dioxide, after oxygen is split off) nor the amounts of hydrogen (the substance left from water, after oxygen is split off) are adequate to account for the atmospheric oxygen content. Hydrogen, to be sure, would be expected to escape from Venus. But the escape rate of hydrogen from the atmosphere of Venus was found to be so low that a preliminary report concluded: "If Venus ever possessed a large amount of water, it cannot have lost it by escape mechanisms known to be operating now."
Significance for evolutionary models
Therefore, for the present, it is reasonable to assume that much of the atomic and molecular forms of oxygen found were present in the Venusian atmosphere from its formation. This would imply in turn, in the context of evolutionary models, that the primordial atmosphere of Earth too must have contained oxygen, since both Earth and Venus were supposed to have been formed from the same primordial gas cloud.
As current postulates go, Earth and the other inner planets, Mercury, Venus, and Mars, all lost their initial atmosphere soon after their formation. This idea gained currency on the strength of find ing only low concentrations of the heavy noble gases—neon, argon and xenon—in our atmosphere. Scientists reasoned that since these inert gases are abundant in the universe, the primordial atmosphere of our planet also must have contained high levels of these gases. As their selective loss from Earth's atmosphere could not be imagined, scientists suggested the loss of the entire "early" atmosphere of Earth and those of our immediate neighbor planets.
The discovery of comparatively massive amounts of argon-36 and argon-38 gases in the atmosphere of Venus strongly contradicts this postulate. These gases are considered primordial in origin because they do not arise out of radioactive decay of heavier elements and because they are so inert that they are not used up in chemical transformations. This means that they had to be present in the original mixture of elements from which Venus was formed.
If the primordial gases of Venus were not lost, then it is likely that the primordial gases of Earth were not lost either. Further, since the atmospheres of Venus and Earth are so dissimilar, the suggestion that both originated from the same, original primordial gas mixture becomes highly unlikely.
Creationists do not claim special in sights into the processes that brought about the solar system. Further, they disclaim any ability to predict characteristics of the yet undiscovered aspects of the solar system by extrapolating from the known to the unknown. God, in their view, has the freedom and ability to fashion planets with any number of similar or dissimilar features. In the variety within the solar system they perceive the signature of its Creator.