The Earth has one satellite, the Moon, lying 384,000 km away from it. The data for the Moon are as follows: mass, 1/81.5 of the mass of the Earth; equatorial diameter, 3476 km; inclination of orbit to planetary orbit, 5°9'; inclination to planetary equator, 18°18'; and density, 3.34. With respect to distance from planet and equatorial diameter, the Moon should belong to the first group. However, this system undoubtedly con stitutes an anomaly, because of the very large size and mass of the satellite relative to the primary.
Now let us consider the system of the Sun and the planets, and let us see whether the same regularities as were observed for the planet-satellite systems exist in this larger system. When we arrange the planets accord ing to their distances from the Sun, we see that the planets (or solar satellites) fall into four groups. The first group contains Mercury, Venus, Earth, Mars, and the asteroids (a fragmented planet). The table shows the relevant characteristics for this group of planets.
These four planets should be placed in one group. Moreover, if the asteroids are considered to be a fragmented planet, the first satellite group of the Sun will contain five members, the same number as the first group of the system of Saturn. The distances between the planets gradually increase with increasing distance from the Sun, a situation similar to that observed in the systems of the giant planets.
The second group in the solar system contains the two very large planets Jupiter and Saturn. It is noteworthy that the second groups in the systems of Jupiter and Saturn also each have two satellites in them, and that these (with the exception of Hyperion) are the largest in each system. It is thus likely that this constitutes a general regularity for both the system of the Sun and the systems of the planets, although exceptions do exist.
The following table lists the basic characteristics of Jupiter, Saturn, Uranus, and Neptune.
It is the opinion of the author that, with respect to size, mass, and chemical composition, Uranus and Neptune constitute an independent, third group of planets of the solar system. This is corroborated by the fact that from Venus out to Saturn the distances between planets consistent ly increase, whereas from Saturn to Pluto these distances remain about the same (1.5 billion km, on the average).
Pluto, which is 5.905 billion km from the Sun, has been studied less than the other planets. Its diameter is approximately half that of the Earth. Different explanations have been suggested for the origin of Pluto. For instance, it has been proposed that Pluto was captured by the Sun as an already-formed planet, that it is a former satellite of Neptune, and that it is a large member of a second asteroid belt located beyond Neptune.
By virtue of the existence of four satellite groups in the systems of Jupiter and Saturn, the author is led to the assumption that the Sun also has four groups of satellites (planets), and that Pluto belongs to the fourth group.
Consequently, it is possible that other planets belonging to this fourth group exist beyond Pluto. If the regularity of the distances between planets continues to be observed further out, then the next planet beyond Pluto ("Transpluto") should be 1.5 billion km from Pluto (about 50 astronomical units from the Sun). The inclination of the orbit of this planet should be approximately the same as that of Pluto, and the planet should be smaller in size than Pluto.
An analysis of the regularities existing in the system of the Sun and its satellites (planets) has led the author to conclude that these regulari ties are analogous to those of the systems of Jupiter and Saturn. A complete classification of the distribution of matter throughout the solar system, according to zones, is presented in the table on the inset page. We assume that the following things are possible: 1) the existence of planets beyond Pluto; 2) the presence of satellites between Io and Europa in the first group of Jupiter; 3) the presence of outer satellites of Saturn in addition to Iapetus and Phoebe; 4) the existence of additional satellites of Uranus and Neptune, especially in the first group of Neptune, and also in the group of Nereid and in the other places in the table where we have placed question marks.
A study of this table brings up several important questions, and any adopted cosmogonic hypothesis concerning the origin and evolution of the solar system must find answers to them. In particular, how can we explain the existence of four groups of satellites in each of the main systems of the solar system (the systems of the Sun, Jupiter, and Saturn)? Moreover, if this is related to the fact that the Sun and the planets went through the same four stages during their development, then what were the stages and how did they differ from one another? What types of nuclear reactions took place in the Sun and what processes occurred on the planets during each of these four stages? Why are the planetary satellites of the first and second groups located within definite spatial intervals from their planets, and why is it that the second groups have two members, the largest satellites in the system? Finally, how can we explain the fact that approximately the same distances separate the third and fourth groups of the Jupiter and Saturn systems? There are also several other questions which come up, but the answers to these require a further development of our cosmogonic concepts, and this is difficult to accomplish within the framework of the present article.