Ron Brand, age 10, of Peoria, Illinois, for his question:
Do we know how planets are formed?
The planet we know best is the earth because, after all, it is our home in the heavens. Scientists have pieced together a lot of its past history from evidence in its rocky surface. They also have figured out that it obeys certain mighty laws of the universe. From these and other known facts, we can guess how this planet was formed. However, an educated guess is just a theory. We cannot state that a theory is a known fact until we have enough evidence to prove it.
In the past, people thought that the earth was the only planet in the universe. Later they learned that the sun has eight other planets and that our Solar System is a family of heavenly bodies, surrounded by vast oceans of space. Modern scientists tell us that other starry suns also have planets. In fact, maybe most of the stars in the universe have solar systems. And in our galaxy alone, there are about 100 billion far flung stars. Then there may be countless billions of planets in the universe.
All these planets belong to solar systems more or less like our own. Each family orbits around a star, much as our planets orbit the sun. No doubt many of them also have moons. And certainly every planetary family must obey the same laws that govern our Solar System. These laws that mold the planets and govern their motions have ruled the whole universe since its beginning.
We now know that new stars are being born and old stars are dying. Most astronomers suspect that a new star is born from a vast cosmic cloud of dust and gases. And most astronomers suspect that the starry sun and its planets were formed together from the same huge, hazy cloud. However, no one is certain about how the formation of a solar system gets started. We can only suggest a theory to explain the steps that mold a vast cloud of gases into a sun with orbiting planets.
Most experts think that for some reason the gaseous cloud begins to contract, or shrink. Its fine particles come closer together. It becomes denser, with most of its material wadded together in the center. Great cosmic forces then start it spinning around, faster and faster. The huge heavy center will become a starry sun, but so far it has not started to blaze. The other material forms banded rings, circling around the center. Gradually the material in these rings wads together and forms a family of orbiting planets. Sometimes a ring also forms a smaller wad that becomes a moon. At last, the huge sun catches fire and the dark solid planets are bathed in daylight. We are not certain that this is exactly how planets are formed. But from what we know at present this theory seems logical.
From evidence in the earth's rocks, scientists knew that our planet must be around four billion years old. Then the lunar rocks proved that the moon is older than four billion years. The earth must be older than we thought. But we need a lot more evidence to prove exactly when and exactly how our planet was formed. Until we know for sure, we can only guess how the earth and all the other planets were born.